research plant based diet

Embracing a plant-based diet

Focusing on whole foods from plant sources can reduce body weight, blood pressure and risk of heart disease, cancer and diabetes — and it can make your environmental impact more sustainable. Stanford Healthy Living instructor Dr. Reshma Shah offers simple ways to incorporate more plants into your diet.  

Your diet is one of the first places to start if you’re looking to manage your health and weight. Focusing on whole foods from plant sources can reduce body weight, blood pressure and risk of heart disease, cancer and diabetes — and it can make your environmental impact more sustainable.

But how do we embrace plants in our diets if we’re so accustomed to including meat and dairy as primary nutrition sources?

We spoke with Dr. Reshma Shah, a physician, plant-based eating advocate, co-author of “Nourish: The Definitive Plant-Based Nutrition Guide for Families” and Stanford Healthy Living instructor, about simple ways to incorporate more plants into your diet and the benefits this can provide for both you and the planet.  

Focus on whole, minimally processed foods.

People use many different terms to describe a plant-based diet, including vegetarian, lacto-ovo vegetarian, pescatarian, and flexitarian to name a few. The most restrictive is veganism, which  excludes all animal products, including meat, eggs and dairy. 

While there are health benefits to adopting a vegan diet, highly processed foods with little to no nutritional value, like Oreos or French fries, could still be a legitimate part of a vegan diet.

In contrast, a whole-foods, plant-based (WFPB) diet: 

• Emphasizes whole, minimally processed foods
• Limits or avoids animal products
• Focuses on plant nutrients from vegetables, fruits, whole grains, legumes, seeds and nuts 
• Limits refined foods like added sugar, white flour and processed oils 

Recommendations from organizations including the U.S. Dietary Guidelines for Americans, World Health Organization, American Diabetes Association and American Cancer Society tout the benefits of plant-based whole foods and caution against high amounts of red and processed meats, saturated fats, highly refined foods and added sugar. 

The vast majority of what nutritional experts are saying reflects the mantra made famous by Michael Pollen in his book “The Omnivore’s Dilemma” — eat food, mostly plants, not too much . 

Eating a plant-based diet helps the environment.

According to a report by the U.S. Food and Agriculture Organization, “The meat industry has a marked impact on a general global scale on water, soils, extinction of plants and animals, and consumption of natural resources, and it has a strong impact on global warming.” 

The meat and dairy industries alone use one third of the Earth’s fresh water , with a single quarter-pound hamburger patty requiring 460 gallons of water — the equivalent of almost 30 showers — to produce.

Reducing your meat and dairy consumption, even by a little, can have big impacts. If everyone in the U.S. ate no meat or cheese just one day a week, it would have the same environmental impact as taking 7.6 million cars off the road.

Plant-based diets prevent animal cruelty. 

Ninety-four percent of Americans agree that animals raised for food deserve to be free from abuse and cruelty , yet 99% of those animals are raised in factory farms, many suffering unspeakable conditions . 

If you would like to lessen your meat and dairy consumption due to animal welfare concerns but aren’t ready to eliminate all animal products from your diet, then you can start by taking small steps, like going meatless one day a week or switching to soy, almond or oat milk. Shah admits that initially she was not ready to give up animal products entirely. 

“I think it is a process and recommend that people go at the pace that feels comfortable for them.” 

Plant-based diets include all nutrients — even protein.

According to the American Dietetic Association, “appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, and for athletes.”

Shah says that there are a few key nutrients that strict vegans and vegetarians should keep in mind, including B12, iron, calcium, iodine, omega-3 fatty acids and vitamin D, but all of these can be obtained through plant-based foods, including fortified plant-based milks, fresh fruits and vegetables or supplemental vitamins, if needed. 

“I think the number one concern for people is that they won’t be able to get enough protein eating a plant-based diet. I also think that people widely overestimate the amount of protein they need.”

All plant foods contain the nine essential amino acids required to make up the proteins you need, and many vegetarian foods like soy, beans, nuts, seeds and non-dairy milk products have comparable amounts of protein to animal foods. 

“Ninety-seven percent of Americans meet their daily protein requirements, but only 4% of Americans meet their daily fiber requirements . I’ve never treated a patient for protein deficiency. If you eat a wide variety of foods and eat enough calories, protein should not be a concern.”

Savor the flavor of plant-based foods. 

Adopting a plant-based diet does not mean subsisting on boring, tasteless food. Shah enjoys incorporating flavorful, varied dishes from around the world, including Ethiopia, Thailand and her native India. 

To get started on your plant-forward journey:

• Start small: Start with adding a “Meatless Monday” to your meal plan and investigate one simple and delicious recipe to try each week. Once you have identified a few favorites, you can add them to your rotation and maybe go meatless one or two days a week. You can learn a few easy techniques to incorporate in many dishes, like roasting vegetables or blending quick and easy soups. 
• Change your plate proportions: Instead of giving up your meat-based protein completely, try to reduce the space it takes on your plate. Instead of a quarter-pound sirloin steak or a full serving of roasted chicken, try a vegetable-heavy stir-fry with a few slices of beef or a salad with chicken. Once your palate and mindset have adjusted to the smaller quantity of meat, try replacing it occasionally with plant-based proteins like tofu, seitan or beans.  
• Be prepared when dining out: If possible, try to examine the restaurant menu ahead of your meal, so you’ll arrive with a plan of what you can eat. Ask for the vegan options and don’t be afraid to request substitutions or omissions for your dish. Fortunately, with more people choosing a vegetarian lifestyle, many restaurants now provide tasty, meat-free options to their customers. 
• Share a dish: Bring a dish to share at a party or potluck; this will lessen your worries about food options. Let your host know ahead of time that you are planning on bringing a dish or, if that is not possible, be upfront and find out if any modifications can be made to accommodate your preferences. Often a simple solution can be found with a little advanced planning.
• Accommodate family members: It can be tricky when one family member is ready to commit to a new diet and lifestyle while others are not. Shah recommends approaching this situation compassionately and allowing for flexibility, if possible. Hopefully your family will be willing to support you even if they are not ready to make the same commitments. Communication is key, and Shah says that the conversation is over the minute someone feels judged, so try to look for points of compromise to reach an amicable solution. 
• Feeling satisfied: A diet of nothing but lettuce and vegetables will leave you feeling hungry and unfulfilled. Be sure to bulk up your meals with filling, fiber-rich whole grains, plant-based proteins and healthy fats. Plant-based meat substitutes like Beyond Beef, seitan and veggie burgers can also be a satisfying choice when you are craving your favorite meat-based comfort food.

Remember that small, consistent changes can add up to big benefits for your health and the planet. Treat yourself and others with compassion as you embrace this new lifestyle, and take time to enjoy the different flavors and textures you discover in your journey.

“It is a really delicious, healthful, sustainable and compassionate way of eating. It doesn’t have to be perfect. Just start simply, do what feels comfortable for you and your family, and don’t forget to celebrate the joy of eating and connection around food.” 

Dr. Reshma Shah will be teaching a plant-based online cooking class with Healthy Living this summer on Tuesday, July 13, from 4:00 – 5:30 p.m.

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• Published: 21 January 2021

Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake

• Kevin D. Hall   ORCID: orcid.org/0000-0003-4062-3133 1 ,
• Juen Guo 1 ,
• Amber B. Courville   ORCID: orcid.org/0000-0002-1419-3937 1 ,
• James Boring 2 ,
• Robert Brychta   ORCID: orcid.org/0000-0001-9491-7968 1 ,
• Kong Y. Chen   ORCID: orcid.org/0000-0002-0306-1904 1 ,
• Valerie Darcey   ORCID: orcid.org/0000-0002-5053-4567 1 ,
• Ciaran G. Forde   ORCID: orcid.org/0000-0002-4001-9182 3 ,
• Ahmed M. Gharib 1 ,
• Isabelle Gallagher 1 ,
• Rebecca Howard 1 ,
• Paule V. Joseph   ORCID: orcid.org/0000-0002-1198-9622 4 , 5 ,
• Lauren Milley 1 ,
• Ronald Ouwerkerk   ORCID: orcid.org/0000-0003-3882-9757 1 ,
• Klaudia Raisinger 2 ,
• Irene Rozga 1 ,
• Alex Schick   ORCID: orcid.org/0000-0003-3015-9138 1 ,
• Michael Stagliano 1 ,
• Stephan Torres   ORCID: orcid.org/0000-0003-4048-1665 2 ,
• Mary Walter 1 ,
• Peter Walter 1 ,
• Shanna Yang 2 &
• Stephanie T. Chung 1  

Nature Medicine volume  27 ,  pages 344–353 ( 2021 ) Cite this article

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• Fat metabolism
• Feeding behaviour

The carbohydrate–insulin model of obesity posits that high-carbohydrate diets lead to excess insulin secretion, thereby promoting fat accumulation and increasing energy intake. Thus, low-carbohydrate diets are predicted to reduce ad libitum energy intake as compared to low-fat, high-carbohydrate diets. To test this hypothesis, 20 adults aged 29.9 ± 1.4 (mean ± s.e.m.) years with body mass index of 27.8 ± 1.3 kg m −2 were admitted as inpatients to the National Institutes of Health Clinical Center and randomized to consume ad libitum either a minimally processed, plant-based, low-fat diet (10.3% fat, 75.2% carbohydrate) with high glycemic load (85 g 1,000 kcal −1 ) or a minimally processed, animal-based, ketogenic, low-carbohydrate diet (75.8% fat, 10.0% carbohydrate) with low glycemic load (6 g 1,000 kcal −1 ) for 2 weeks followed immediately by the alternate diet for 2 weeks. One participant withdrew due to hypoglycemia during the low-carbohydrate diet. The primary outcomes compared mean daily ad libitum energy intake between each 2-week diet period as well as between the final week of each diet. We found that the low-fat diet led to 689 ± 73 kcal d −1 less energy intake than the low-carbohydrate diet over 2 weeks ( P  < 0.0001) and 544 ± 68 kcal d −1 less over the final week ( P  < 0.0001). Therefore, the predictions of the carbohydrate–insulin model were inconsistent with our observations. This study was registered on ClinicalTrials.gov as NCT03878108 .

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Data availability

The study protocol, de-identified individual data, and statistical analysis code for the results reported in this manuscript will be posted on the Open Science Framework website ( https://osf.io/fjykq/ ) and is freely available without restrictions.

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Acknowledgements

This work was supported by the Intramural Research Program of the NIH, National Institute of Diabetes & Digestive & Kidney Diseases under award number 1ZIADK013037. P.V.J. is supported by the National Institute of Nursing Research under award number 1ZIANR000035-01, The Office of Workforce Diversity and the Rockefeller University Heilbrunn Nurse Scholar Award. We thank the nursing and nutrition staff at the NIH Metabolic Clinical Research Unit for their invaluable assistance with this study. We thank K. Klatt, J. Speakman and E. Weiss for helpful comments. We thank the study participants who volunteered to participate in this demanding protocol.

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K.D.H. designed the study. K.D.H. and J.G. analyzed the data. A.C. and S.Y. designed the diets and measured food and beverage intake with the assistance of J.B. and S.T. R.B. and K.Y.C. performed the indirect calorimetry measurements. C.G.F. assisted with the appetitive and eating rate measurements and their interpretation. A.M.G. and R.O. performed the liver fat measurements. M.W. and P.W. analyzed the blood and urine samples. S.T.C., I.R. and M.S. were responsible for the clinical care of the research participants and supervised the day-to-day operation and coordination of the study by V.D., I.G., R.H., L.M., P.V.J., K.R. and A.S. K.D.H. wrote the manuscript and is the guarantor of this work and has full access to all data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. All authors critically revised the draft and approved the final manuscript.

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Correspondence to Kevin D. Hall .

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C.G. Forde has received reimbursement for speaking at conferences sponsored by companies selling nutritional products, serves on the scientific advisory council for Kerry Taste and Nutrition and is part of an academic consortium that has received research funding from Abbott Nutrition, Nestec and Danone. The other authors declare no competing interests.

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Extended data

Extended data fig. 1 oral glucose tolerance..

Mean blood concentrations in response to 75g oral glucose tolerance tests conducted at the end of the LC and LF diet periods (n=20) with respect to a ) glucose, b ) insulin, c ) lactate, and d ) free fatty acids. Data are presented as mean ± SEM.

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Supplementary information.

Descriptions and photographs of seven daily menus for LC and LF diets plus snacks.

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Hall, K.D., Guo, J., Courville, A.B. et al. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nat Med 27 , 344–353 (2021). https://doi.org/10.1038/s41591-020-01209-1

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What Is a Plant-Based Diet? A Complete Beginner’s Guide

Dropping the phrase “plant-based diet” is trendy when you’re talking nutrition these days. Why?  Lauren Manaker, RD , based in Charleston, South Carolina, suspects it’s because of increased awareness of the health and environmental benefits that are associated with eating this way.

Some of that could be the result of documentaries that throw shade at eating meat and other animal products, such as  You Are What You Eat: A Twin Experiment (2024), Game Changers (2018), and Cowspiracy  (2014).

But what does “plant-based diet” mean, anyway? Is it the same thing as being  vegetarian  or  vegan ? Or does this diet just mean you make an effort to pack more veggies into your meals?

Technically, all of the above interpretations are correct. “Some people use the term ‘plant-based diet’ as a synonym for the vegan diet,” says Summer Yule, RD , who is based in Hartford, Connecticut. “Others may use the term in a broader way that includes all vegetarian diets, and I’ve also seen people use ‘plant-based’ to mean diets that are composed mostly, but not entirely, of plant foods.”

How a Plant-Based Diet Works

The idea of a plant-based diet is to make plant-based foods the central part of your meals. Simple, right?

“A plant-based diet emphasizes foods like fruits, vegetables, and beans, and limits foods like meats, dairy, and eggs,” Manaker says. From there, more restrictions could be put in place depending on how strict you want to be. “It may completely eliminate foods from animals or just limit intake, depending on the individual’s interpretation,” Manaker says.

Common Questions & Answers

What beginners should know about plant-based eating.

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Types of plant-based diets.

Think of “plant-based” as a broad category, with other more specific diets falling under its umbrella. For example, the Mediterranean diet is a version of a plant-based diet because even though it incorporates fish and poultry, the emphasis is on plant-based foods, Manaker says.

Plant-based diets include:

• Pesco vegetarian
• Semivegetarian or flexitarian
• Ovo vegetarian
• Lacto vegetarian
• Lacto-ovo vegetarian

Whole30 , a popular diet and lifestyle plan, doesn’t usually qualify. “The Whole30 diet traditionally is heavier on animal proteins, though it is possible to follow this diet in a plant-based way,” Manaker says.

Potential Health Benefits of a Plant-Based Diet

Indeed, most people who adopt this way of eating do it for the potential health benefits. “There have been many cardiac benefits linked to eating this way, like reduced cholesterol,” Manaker says. “Some studies suggest that eating a plant-based diet may improve fertility parameters, and it also may reduce your risk of developing [type 2] diabetes.”

As the following research suggests, a plant-based diet may help reduce the likelihood that you’ll need medication, lower your risk of obesity and high blood pressure, and maybe even help prevent or manage type 2 diabetes and heart disease. Here’s a closer look at possible plant-based diet benefits.

A Reduced Risk for Type 2 Diabetes

Manaker agrees that a plant-based diet can help you manage your weight, and may even lead to weight loss if you follow it in a healthy way. “Most people [who transition from a typical American diet] also start to feel like they have more energy,” she adds.

A Healthier Weight and Blood Sugar Level in People With Diabetes 

A reduced risk of heart disease , a reduced risk of cancer, a healthier brain, a longer life , can a plant-based diet help you lose weight.

Although there are plenty of reasons you may want to adopt a plant-based diet, from a lower risk for chronic diseases to a reduced carbon footprint, weight loss may be another outcome you’re after.

Good news: A plant-based diet can help with weight loss, too.

Are There Any Disadvantages to a Plant-Based Diet?

Simply sticking with plant-based foods likely isn’t going to cut it — you’ll need to pay attention to the quality of the foods you’re consuming, because there are plenty of unhealthy foods that qualify as plant-based, such as potato chips and french fries. Unhealthy plant-based foods will increase your risk of weight gain and health conditions such as heart disease .

For the most part, eating a plant-based diet will check the boxes of all the major nutrients. “A well-planned plant-based diet can be nutritionally adequate and particularly rich in fiber, vitamin A, vitamin C, and potassium because of all the fruits and vegetables that are typically eaten,” Yule says.

That said, if you decide to take the plant-based diet to the next level and swear off all animal products, you may need to keep an eye on your levels of vitamin B12 and choline. “Vitamin B12 is found primarily in animal sources, and the two best sources of choline are egg yolks and liver,” Manaker says. “If a person is avoiding animal products, they may not be taking in enough of these nutrients.”

A Food List of What to Eat, Limit, and Avoid on a Plant-Based Diet

What to eat and drink.

• Vegetables (including kale, spinach, Swiss chard, collard greens, sweet potatoes, asparagus, bell peppers, and broccoli)
• Fruits (such as avocado, strawberries, blueberries, watermelon, apples, grapes , bananas, grapefruit, and oranges)
• Whole grains (such as quinoa, farro, brown rice, whole-wheat bread, and whole-wheat pasta)
• Nuts (walnuts,  almonds , macadamia nuts, and cashews all count)
• Seeds (such as flaxseed, chia seeds, and hemp seeds)
• Tea (including green, lavender, chamomile, or ginger)

What to Limit (or Avoid Entirely, Depending on the Plan You Choose)

• Dairy (including milk and cheese)
• Meat and poultry (like chicken, beef, and pork)
• Processed animal meats, such as sausages and hot dogs
• All animal products (including eggs, dairy, and meat if you’re following a vegan diet)
• Refined grains (such as “white” foods, like white pasta, rice, and bread)
• Sweets (like cookies, brownies, and cake)
• Sweetened beverages, such as soda, and fruit juice
• French fries
• Honey (if vegan)

A 7-Day Sample Menu for a Standard Plant-Based Diet

Breakfast  Tofu scramble

Lunch  Cauliflower rice bowl with black beans, corn, avocado, and salsa

Dinner  Veggie-topped pizza

Snack  Zucchini chips

Breakfast  Oatmeal-based breakfast muffins

Lunch  Tomato basil soup with oyster crackers

Dinner  Veggie stir-fry with tofu

Snack  Hummus wrap

Breakfast  Homemade oatmeal bars

Lunch  Greek salad with a slice of whole-grain pita bread

Dinner  Kale and tofu curry

Snack  Cashew yogurt with berries and a scoop of peanut butter

Breakfast  Breakfast burrito with eggs, peppers, and salsa

Lunch  Veggie burger and a side salad

Dinner  Cauliflower “steak” with roasted sweet potato fries

Snack  Veggies with hummus

Breakfast  Dairy-free yogurt with berries and granola

Lunch  Tomato sandwich with pesto and a drizzle of olive oil

Dinner  Whole-wheat pasta with roasted tomatoes

Snack  Roasted chickpeas

Breakfast  Chia seed pudding with fresh berries and a spoonful of almond butter

Lunch  Avocado toast

Dinner  Vegan mushroom enchiladas

Snack  Handful of almonds

Breakfast  Oatmeal with almond milk

Lunch  Quinoa bowl with roasted carrots and sweet potatoes

Dinner  Vegetarian chili topped with slices of avocado

Snack  Whole-wheat toast topped with peanut butter

5 Tips for Plant-Based Diet Beginners

1. think outside of the produce aisle.

Stock up on grains, canned beans, and canned or frozen fruits and veggies so you don’t have to shop every few days.

2. Swap Meat for High-Protein Legumes

Tofu, tempeh, black beans, chickpeas, pinto beans, and dried peas are some of your many options. You can also use plant-based protein powder and certain other high-protein foods, such as seitan.

3. When Eating Out, Ask the Waiter for Suggestions

Sometimes a server will help you piece together a meal with sides and appetizers if there isn’t a plant-based main course on the menu.

4. Choose Budget-Friendly Options

Keep grocery costs down by buying in-season produce and sticking to simple plant-based foods such as grains, beans, and frozen and canned foods.

5. Keep Nutrition Basics in Mind

Limit the sugar, fat, and refined grains you cook with at home. These ingredients can quickly make a home-cooked plant-based meal unhealthy.

Featured Recipe

Pear, Walnut, and Ginger Oatmeal

Fresh fruit, nuts, and spices make this a.m. meal even heartier, with  walnuts  delivering filling fats, including omega-3s, which  have been shown to be heart-healthy .

CALORIES PER SERVING

Reviewed by, ingredients.

In a medium saucepan over medium-high heat, combine milk with 3 cups of water. Bring to a boil.

Add toasted oats and return to a boil. Lower heat and simmer, stirring occasionally, until most of the liquid has been absorbed, about 20–30 minutes.

Stir in ginger.

Divide oatmeal evenly among 4 serving bowls and top each with one-quarter of pears and walnuts.

Nutrition Facts

Amount per serving.

Serving size 1 bowl

saturated fat

Carbohydrates, added sugar, rate recipe, share recipe.

The plant-based diet is a category of diets that have this in common: “All plant-based diets limit animal-derived foods in favor of plants,” Yule says. Instead of a diet that centers on meat and dairy, the starring roles are played by vegetables, fruits, and whole grains. It’s a fresh, flavorful approach to eating and has been shown to have significant health benefits, including weight loss and disease prevention.

Additional reporting by  Laura McArdle .

Resources We Trust

Best book about plant-based diets.

The Plant-Based Diet Revolution: 28 Days to a Healthier You , by Alan Desmond and Bob Andrews

Best Plant-Based Diet Blog 

Oh She Glows

Oh She Glows ($2.99)

Best Website for Plant-Based Diet Info

Forks Over Knives:   The Beginner’s Guide to a Whole-Food, Plant-Based Diet

Best Podcast for Those Interested in a Plant-Based Diet

PLANTSTRONG

Editorial Sources and Fact-Checking

Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy . We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

• McManus KD. What Is a Plant-Based Diet and Why Should You Try It? Harvard Health Publishing. November 16, 2021.
• Hever J et al. Plant-Based Nutrition for Healthcare Professionals: Implementing Diet as a Primary Modality in the Prevention and Treatment of Chronic Disease. Journal of Geriatric Cardiology . May 2017.
• Caspero A et al. Building a Healthy Vegetarian Diet: Myths and Facts. Academy of Nutrition and Dietetics. October 4, 2021.
• Qian F et al. Association Between Plant-Based Dietary Patterns and Risk of Type 2 Diabetes: A Systematic Review and Meta-Analysis. JAMA Internal Medicine . July 22, 2019.
• Bagust A et al. Deteriorating Beta-Cell Function in Type 2 Diabetes: A Long-Term Model. QJM . April 2003.
• Kahleova H et al. A Plant-Based Dietary Intervention Improves Beta-Cell Function and Insulin Resistance in Overweight Adults: A 16-Week Randomized Clinical Trial. Nutrients . February 2018.
• Medawar E et al. The Effects of Plant-Based Diets on the Body and the Brain: A Systematic Review. Translational Psychiatry . September 12, 2019.
• McMacken M et al. A Plant-Based Diet for the Prevention and Treatment of Type 2 Diabetes. Journal of Geriatric Cardiology . May 2017.
• Toumpanakis A et al. Effectiveness of Plant-Based Diets in Promoting Well-Being in the Management of Type 2 Diabetes: A Systematic Review. BMJ Open Diabetes Research & Care . October 30, 2018.
• Satija A et al. Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults. Journal of the American College of Cardiology . July 25, 2017.
• Kim H et al. Plant-Based Diets Are Associated With a Lower Risk of Incident Cardiovascular Disease, Cardiovascular Disease Mortality, and All-Cause Mortality in a General Population of Middle-Aged Adults. Journal of the American Heart Association . August 20, 2019.
• Choi EY et al. A Plant-Based Diet and Heart Failure: Case Report and Literature Review. Journal of Geriatric Cardiology . May 2017.
• Watling CZ et al. Risk of Cancer in Regular and Low Meat-Eaters, Fish-Eaters, and Vegetarians: A Prospective Analysis of UK Biobank Participants. BMC Medicine . February 24, 2022.
• Rigi S et al. The Association Between Plant-Based Dietary Patterns and Risk of Breast Cancer: A Case-Control Study. Scientific Reports . February 9, 2021.
• Budhathoki S et al. Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality in a Japanese Cohort. JAMA Internal Medicine . August 26, 2019.
• Sterling SR et al. The Potential for Plant-Based Diets to Promote Health Among Blacks Living in the United States. Nutrients . December 2019.
• Ramey MM et al. Markers of a Plant-Based Diet Relate to Memory and Executive Function in Older Adults. Nutritional Neuroscience . February 2022.
• Naghshi S et al. Dietary Intake of Total, Animal, and Plant Proteins and Risk of All Cause, Cardiovascular, and Cancer Mortality: Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies. BMJ . July 22, 2020.
• Miller V et al. Fruit, Vegetable, and Legume Intake, and Cardiovascular Disease and Deaths in 18 Countries (PURE): A Prospective Cohort Study. The Lancet . November 4, 2017.
• Turner-McGrievy G et al. A Plant-Based Diet for Overweight and Obesity Prevention and Treatment. Journal of Geriatric Cardiology . May 2017.
• Huang RY et al. Vegetarian Diets and Weight Reduction: A Meta-Analysis of Randomized Controlled Trials. Journal of General Internal Medicine . January 2016.
• Weight Loss. Physicians Committee for Responsible Medicine.
• Dietary Fiber: Essential for a Healthy Diet. Mayo Clinic. November 4, 2022.
• Springmann M et al. The Global and Regional Costs of Healthy and Sustainable Dietary Patterns: A Modelling Study. The Lancet Planetary Health . November 2021.

10 Benefits of a Plant-Based Diet

One of the easiest ways you can start improving your overall health is by going plant-based. From your gut to your heart and brain, nearly every part of your body benefits when you add more fruits, vegetables, nuts, seeds and legumes to your plate.

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Keep in mind that following a plant-based diet doesn't mean you have to be vegetarian or vegan if you love foods like Greek yogurt, cheese or fish.

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"A plant-based eating pattern may or may not include animal products, but the frequency of animal product consumption and the portion sizes of animal products are smaller than the conventional American diet," Kelly Jones, RDN, CSSD , explains. By including more whole plant foods, you'll get more vitamins, minerals, antioxidants and fiber.

"Incorporating a plant-based lifestyle actually helps people increase variety in their diet," Jones says. "People become more adventurous with vegetables and legumes they've never tried or never given a second chance, and begin adding more flavor, spices and even a greater variety of cuisines into their regular eating pattern."

And don't worry, you'll get enough protein: "Standard portions of proteins, animal-based or not, tend to be much larger than what the body needs for optimal function — and many people don't recognize the protein available from grains, vegetables, nuts and seeds all add up in meals and snacks," Jones says.

So start adding a few animal-free foods to your diet every day — remember, you don't have to overhaul your eating habits all at once — to begin reaping these plant-based diet benefits.

1. It’s Good for Your Gut

"Plant-based diets tend to better support gut health and the microbiome, which science is continuing to tell us impacts many areas of health — from immune system function to metabolism and mood," Jones says.

This is largely due to the fiber and antioxidants, compounds that protect your cells from damage, found in plants. "Since plant foods are the only source of fiber and fermentable carbohydrates known as prebiotics‌ , ‌ and they offer tens of thousands of phytochemical antioxidants, the bacteria in the lower digestive tract are better supported when diets are rich in whole plant foods," Jones says.

Your digestive system is home to about 100 trillion bacteria (both good and bad!), and while everyone has a unique microbiota, certain collections of bacteria are known to be found in healthy people, per Harvard Medical School .

The latest research suggests that certain healthy gut bacteria are linked to lower susceptibility to rheumatoid arthritis and offer a possible treatment or prevent inflammation that contributes to fatty plaque build-up in arteries.

"One of the most fascinating areas of nutrition to me is how it impacts mental health, and studies have shown vegetarian and vegan diets to reduce psychological distress and reports of anxiety, depression and fatigue."

2. It Supports Your Immune System

"Eighty percent of our immune system is in our gastrointestinal tract, and it's good for the immune system to have a healthy microbiome ," says Lauren Graf, RD . "The best way to do that is to feed the good bacteria. A lot of the fiber found in plant foods like bananas and artichokes serves as prebiotics, which are food for probiotics."

Plant foods are also filled with nutrients that can help strengthen your immune system. Just a few of the many helpful vitamins and minerals found abundantly in fruits and vegetables include:

• ‌ Vitamin C: ‌ A 200-milligram daily dose vitamin C appeared to shorten the duration of cold symptoms by 8 percent in adults and 14 percent in children, which equates to about one day less of sickness, per a January 2013 review in the ‌ Cochrane Database of Systematic Reviews . ‌ One large bell pepper contains 233 milligrams of vitamin C.
• ‌ Vitamin E: ‌ Found in high-fat plant foods like peanuts, sunflower seeds, hazelnuts and almonds, vitamin E is part of nearly 200 biochemical reactions in your body and acts as an antioxidant to helps your body fight infection, per the Cleveland Clinic .
• ‌ Zinc: ‌ This mineral has antiviral properties and is found in plant foods such as beans, nuts and whole grains. It has well-established effects on the immune system and even has the potential to be a supportive treatment in people with COVID-19, per an August 2020 review in ‌ Maturitas ‌ . A zinc deficiency can result in immune dysfunction and increase your susceptibility to infection.
• ‌ Vitamin A: ‌ Known as an infection fighter, you can get vitamin A from both animal sources and plant carotenoids. Aim for colorful plant foods like carrots, sweet potatoes, butternut squash, pumpkin, cantaloupe and dark green leafy vegetables, the Cleveland Clinic recommends.

3. It Helps Lower Inflammation

You've likely seen powders and potions that tout antioxidant and anti-inflammatory benefits, but it's really best to get your antioxidants through a plant-based diet.

"When we get our nutrients from whole foods, they tend to be more bioavailable than supplements," Maya Feller, RD, CDN , says. "Plus, when we eat whole foods, in general, we don't worry about toxicity."

Antioxidants are important because they can prevent or delay some types of cell damage. While diets high in vegetables and fruits (great sources of antioxidants) have been found to be healthy, research has not shown that antioxidant supplements are beneficial in preventing disease, per the National Institutes of Health (NIH).

Your body naturally forms free radicals — highly unstable molecules that can cause oxidative stress, a process that leads to cell damage — when you exercise, digest food, smoke or are exposed to sunlight or air pollution, according to the NIH. This oxidative stress is believed to play a role in a variety of diseases such as cancer, heart disease, diabetes, Alzheimer's disease, Parkinson's disease and even eye disease like age-related macular degeneration and cataracts.

"When we think about lowering inflammation with a plant-based diet, it really leads back to gut health," Feller says. "The gut is involved in managing inflammatory properties, and plants have fiber, polyphenols and phytonutrients that all help with reducing inflammation."

4. It Helps You Maintain a Healthy Weight

A large body of evidence shows that fruits and vegetables can help you lose weight .

Eating more vegetables and fruits promotes long-term weight stability or weight loss in women, per a June 2020 review in ‌ Nutrients ‌ . This may be because the fiber in fruits and vegetables helps you to feel satiated faster and because veggies and fruit are low in fat and calories. (It's worth noting that the Hass Avocado Board funded this review, but it's still notable because it specifically looked at how higher vegetable and fruit intake affects weight loss largely in women — and was the first review to do so.)

The review included one prospective study that found the top five fruits for weight loss were blueberries, apples, pears, prunes, strawberries and avocados. Meanwhile, the top five non-legume vegetables for weight loss were broccoli, peppers, summer squash, cauliflower and Brussels sprouts.

What's more, shifting to a plant-based, low-fat diet is linked to increasing the body's metabolism to the point of reducing excess body fat, per a November 2020 study in ‌ JAMA Network Open . ‌ By the end of the trial, the plant-based group had an average 18.7-percent increase in after-meal calorie burn and a lost about 18 pounds, as well as saw a decrease in insulin resistance and body fat — particularly visceral fat, a dangerous type of fat stored around internal organs.

The U.S. Centers for Disease Control and Prevention (CDC) recommends eating more fruits and vegetables as a healthy way to lose or maintain weight. The water and fiber in fruits and vegetables add volume, so you can eat the same amount of food for fewer calories (while still feeling satiated!) when you focus on produce.

Related Reading

A 7-Day Plant-Based Meal Plan to Help You Lose Weight

5. It Keeps Your Heart Healthy

Going plant-based helps you replace unhealthy saturated and trans fats with plant-based fats that contain heart-protective polyunsaturated and monounsaturated fats, Feller says.

And while limiting animal foods can reduce your cholesterol levels, eating more fiber — particularly soluble fiber — actually helps to bind with cholesterol in our gut and pull it out of our bodies, Graf says. "It naturally lowers your cholesterol."

A plant-based diet is tied to a lower risk of diabetes, and diabetes and heart disease often go hand in hand, per the CDC . If you have diabetes, you are twice as likely to have a stroke or heart disease than someone without diabetes (and at a younger age). You're also more likely to have heart disease the longer you have diabetes.

"One thing that a lot of people are surprised by is that plant-based diets are very effective for preventing or reversing insulin resistance," Graf says. "When we look at real clinical trials of people following plant-based diets versus higher-fat animal diets, consuming beans, whole grains, vegetables, fruits, nuts and seeds seems to lower insulin resistance, hemoglobin A1C levels [a measure of sugar in the blood] and your risk for developing type 2 diabetes."

These studies explore the link between conditions involved in heart health and a plant-based eating plan:

• ‌ Blood pressure: ‌ A plant-based diet packed with vegetables and whole grains and limited in refined grains, sugary drinks and meat is linked to lower systolic and diastolic blood pressure levels, per a July 2020 study in the BMJ .
• ‌ Diabetes: ‌ People who adhered more strictly to plant-based diets were observed to have a lower risk of type 2 diabetes than those who did so less strictly in a July 2019 meta-analysis of more than 300,000 participants in ‌ JAMA Internal Medicine ‌ .
• ‌ Cholesterol: ‌ A November 2020 study in ‌ Heart ‌ found that people with obesity (the majority were men) who followed a "green" Mediterranean diet, with plant-based foods replacing meat and fish, had lower cholesterol levels and lost up to 13.6 pounds more than those eating meat on the diet. They also had lower blood pressure.
• ‌ Heart disease: ‌ Researchers used data from 12,168 middle-aged adults who were followed up with from 1987 through 2016 to track the effect of their diets on long-term health in an August 2019 study in ‌ Journal of the American Heart Association ‌ . Those who best adhered to an overall plant-based diet or pro-vegetarian diet were observed to have a 16-percent lower risk of cardiovascular disease, 31- to 32-percent lower risk of cardiovascular disease mortality and 18- to 25-percent lower risk of all-cause mortality than those with the least adherence.

6. It's Linked to a Reduced Risk of Cancer

Eating many plant-based foods has been linked with lower cancer rates, likely because plants produce protective phytochemicals that are anti-inflammatory — plus, they help you eat more fiber, per the Mayo Clinic .

Diets rich in both soluble and insoluble fiber were linked to a lower risk of getting breast cancer before menopause compared to lower-fiber diets, per a March 2016 study published in ‌ Pediatrics ‌ ‌ . ‌

Meanwhile, every 10 grams of fiber daily is linked to a 10-percent reduced risk of colon cancer, according to a November 2011 study in the ‌ BMJ ‌ ‌ . ‌

7. It Benefits Your Brain

A healthy plant-based diet is linked to a lower risk of stroke, according to a March 2021 study in ‌ Neurology ‌.

And researchers found that the Mediterranean-Dash Intervention for Neurodegenerative Delay (MIND) diet is linked to a lower risk of Alzheimer's Disease by up to 53 percent in those who adhere to the diet rigorously and by 35 percent in those who stick to it moderately well, per a February 2015 study in ‌ Alzheimer's & Dementia ‌ ‌ . ‌

The MIND diet emphasizes brain-healthy food groups, which are largely plant-based. It also outlines five unhealthy groups to limit, including red meats, butter and cheese.

"Plant-based diets are linked to better brain health, especially as we age," Jones says. "The MIND diet is very rich in plants with a very small inclusion of animal products, and is well-researched to have an association with improved neurological function and reduced risk of Alzheimer's disease."

A plant-based diet may also be able to influence brain function — though the exact mechanisms are still unclear and more research is needed, per a September 2019 review in ‌ Translational Psychiatry ‌ ‌ . ‌

"One of the most fascinating areas of nutrition to me is how it impacts mental health, and studies have shown vegetarian and vegan diets to reduce psychological distress and reports of anxiety, depression and fatigue," Jones says.

"The Mediterranean diet is one of the most popular plant-based diets and also has links to reductions in depression, anxiety and stress despite the inclusion of fish and very small amounts of meat and poultry."

8. You'll Have More Energy

Plant-based foods are beneficial for your digestive system in several ways, which may help you feel more energized and satiated throughout the day.

"An increase in nourishing carbohydrates, vitamins, minerals and antioxidants — as well as the decrease in saturated fat and heavy animal proteins — can leave people feeling lighter, more energetic and with an improved mood," Jones says.

What's more, although many fad diets emphasize excluding carbs , it's the type of fuel your body prefers.

"In meat-heavy American diets, fat and protein tend to be ingested in higher amounts than needed, so smaller percentages of energy come from carbs," Jones says. "While this may sound in line with some trendy diets, carbs are the most efficient and preferred source of energy for the muscles and the central nervous system. Shifting to a more plant-based diet increases intake of the usable energy that our bodies thrive off."

"We also think of antioxidants as beneficial for long-term health, but in the short term, they work synergistically with each other as well as with our macronutrients, vitamins and minerals to support our metabolism, reduce inflammation and play a role in immune function. This can in turn improve energy levels and mental clarity," Jones adds.

Plant-based diets help improve blood thickness, helping more oxygen reach the muscles and improving athletic performance, per a January 2019 review in ‌ Nutrients ‌ ‌ . ‌ They also improve arterial flexibility and diameter to lead to better blood flow while a single high-fat meal can impair arterial function for several hours.

You may not even realize how sluggish you're feeling until you make the shift to a plant-based diet. "When you're eating food that's easier for our body to break down, I believe that can improve energy levels," Graf says. "Sometimes, people will say they didn't realize how bad they were feeling or how much better they could feel until they changed their habits."

9. It's Linked to a Lower Risk of Osteoporosis

More research is needed, but some theoretical findings suggest that a long-term plant-based diet is associated with lower rates of osteoporosis, per an August 2020 review in ‌ Current Opinion in Endocrinology, Diabetes and Obesity ‌ .

There's also no evidence that a plant-based diet, when followed carefully to maintain adequate calcium and vitamin D levels, has negative effects on bone health.

10. It's Tied to a Lower Risk of Kidney Disease

Although there were once concerns about protein and amino acid deficiencies with plant-based proteins in people with chronic kidney disease (CKD), those were debunked years ago.

A March 2019 paper in the ‌ Journal of Renal Nutrition ‌ concluded that not only can you eat a plant-based protein diet if you have chronic kidney disease, but it may even improve your condition.

"Those substituting animal-based proteins for plant-based proteins have shown reductions in severity of hypertension [high blood pressure], hyperphosphatemia [an electrolyte disorder] and metabolic acidosis [an accumulation of acid in the body]," note the researchers.

9 Plant-Based Product Swaps for Your Go-To Foods, From Cheese to Yogurt to Eggs

• Harvard Medical School: "Can gut bacteria improve your health?"
• Harvard Medical School: "Should I be eating more fiber?"
• Mayo Clinic: "Chart of high-fiber foods"
• Cochrane Database of Systematic Reviews: "Vitamin C for preventing and treating the common cold"
• Cleveland Clinic: "8 Vitamins & Minerals You Need for a Healthy Immune System"
• Maturitas: "Immune-boosting role of vitamins D, C, E, zinc, selenium and omega-3 fatty acids: Could they help against COVID-19?"
• National Institutes of Health: "Antioxidants: In Depth"
• Nutrients: "A Comprehensive Critical Assessment of Increased Fruit and Vegetable Intake on Weight Loss in Women"
• JAMA Network Open: "Effect of a Low-Fat Vegan Diet on Body Weight, Insulin Sensitivity, Postprandial Metabolism, and Intramyocellular and Hepatocellular Lipid Levels in Overweight Adults"
• U.S. Centers for Disease Control and Prevention: "Using Fruits & Vegetables to Manage Your Weight"
• U.S. Centers for Disease Control and Prevention: "Diabetes and Your Heart"
• Journal of Hypertension: "The effect of plant-based dietary patterns on blood pressure a systematic review and meta-analysis of controlled intervention trials"
• National Institutes of Health: "DASH Eating Plan"
• JAMA Internal Medicine: "Association Between Plant-Based Dietary Patterns and Risk of Type 2 Diabetes"
• Heart: "The effect of green Mediterranean diet on cardiometabolic risk; a randomised controlled trial"
• Journal of the American Heart Association: "Plant‐Based Diets Are Associated With a Lower Risk of Incident Cardiovascular Disease, Cardiovascular Disease Mortality, and All‐Cause Mortality in a General Population of Middle‐Aged Adults"
• Pediatrics: "Dietary Fiber Intake in Young Adults and Breast Cancer Risk"
• The BMJ: " Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies"
• Current Opinion in Endocrinology, Diabetes and Obesity: "Plant-based diets and bone health: sorting through the evidence"
• Journal of Renal Nutrition: "Adequacy of Plant-Based Proteins in Chronic Kidney Disease"
• Alzheimer's & Dementia: "MIND Diet Associated with Reduced Incidence of Alzheimer’s Disease"
• Translational Psychiatry: "The effects of plant-based diets on the body and the brain: a systematic review"
• Nutrients: "Plant-Based Diets for Cardiovascular Safety and Performance in Endurance Sports"
• USDA: "Sweet Red Bell Peppers"
• BMJ: "https://nutrition.bmj.com/content/early/2020/07/07/bmjnph-2020-000077"
• Neurology: "Quality of Plant-based Diet and Risk of Total, Ischemic, and Hemorrhagic Stroke"

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Stanford study maintains that plant-based diet lives up to its hype after testing with identical twins: 'A vegan diet is healthier'

A study by Stanford Medicine has revealed compelling data about why a plant-based diet can be better for your health compared to regularly eating meat. 

According to Sci Tech Daily , the 2022 trial saw 22 pairs of identical twins take part, with one twin eating a vegan diet for eight weeks and the other adapting an omnivore diet during the same period. Both diets were healthy, featuring plenty of fruits, vegetables , and whole grains, while sugar and starch was avoided.

Of the 44 participants, only one person failed to complete the eight-week period — that twin was in the vegan group.

After just four weeks, the benefits of the plant-based diet were clear to see, with those shunning meat reporting lower insulin levels, reduced body weight, and lower low-density lipoprotein cholesterol (LDL-C) levels.

High levels of those three factors have been linked to poor cardiovascular health, while raised insulin readings increase the risk of diabetes.

These findings were discovered in participants with already healthy LDL-C levels, and the scientists predicted that greater improvements would be seen for those who already have high LDL-C readings.

This study didn't even take into account the benefits of a plant-based diet in terms of environmental health. According to research published in the Nature Food journal and summarized by the Guardian , a vegan diet produces 75% less planet-warming pollution compared to diets in which 100 grams of meat a day are consumed.

Meanwhile, that study also revealed that wildlife destruction is decreased by 66% with a vegan diet, while water use is reduced by 54%. 

As Stanford study leader Christopher Gardner — a Rehnborg Farquhar professor and a professor of medicine — noted, getting everyone to adapt to a vegan diet might be difficult despite the benefits. But even making plant-based meals more of a focus can significantly affect health.

Gardner added: "Not only did this study provide a groundbreaking way to assert that a vegan diet is healthier than the conventional omnivore diet, but the twins were also a riot to work with."

"A vegan diet can confer additional benefits such as increased gut bacteria and the reduction of telomere loss, which slows aging in the body," Gardner said. "What's more important than going strictly vegan is including more plant-based foods into your diet. Luckily, having fun with vegan multicultural foods like Indian masala, Asian stir-fry, and African lentil-based dishes can be a great first step."

As Gardner observed, even small changes can make a difference to health, and there are plenty of delicious options to fill the gap meat leaves behind.

Stanford study maintains that plant-based diet lives up to its hype after testing with identical twins: 'A vegan diet is healthier' first appeared on The Cool Down .

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• Nutrition and healthy eating
• Add antioxidants to your diet

Antioxidants are certain nutrients, such as vitamins C or E, or carotenoids, which may help protect cells against daily damage. As cells do their job, the way they process oxygen results in a molecule called a free radical. These molecules are unstable. As they regain stability, free radicals damage cells and DNA.

Disease and free radical damage

Over time, free radical damage can cause problems for tissues and organs in the body, potentially leading to disease. Research suggests that free radical molecules can add to the risk of health issues linked to aging. Some examples are heart disease, age-related macular degeneration, Alzheimer's disease and cancer.

The body's cells can fix or prevent free radical damage, for example, by making antioxidant enzymes. And some antioxidants, such as vitamin C, come from food and drink.

Eating antioxidants

Plant-based foods are the best source of antioxidants. These include fruits, vegetables, whole grains, nuts, seeds, herbs and spices, and even cocoa. Plants have naturally occurring antioxidants such as carotenoids, flavonoids, isothiocyanates, and phenolic acids.

As a bonus, many foods that have antioxidants also have other benefits. They are often high in fiber, low in saturated fat and cholesterol, and good sources of vitamins and minerals.

Artichokes are a good example.

They naturally have the fiber inulin. But artichokes also have plant chemicals called flavonoids and phenolic acids. Those phytonutrients have the potential to help manage free radicals.

Does cooking affect antioxidants?

Drying, cooking or freezing foods can affect its level of antioxidants. Sometimes cooking allows an antioxidant to be better absorbed. Lycopene in tomatoes is one example.

More lycopene is available in cooked tomatoes than raw ones. And for some foods, such as sweet potatoes, cooked is the only way we could eat them at all.

In addition to cooking, some antioxidants are more available when paired with another nutrient. One example is orange and yellow vegetables with beta carotene and vitamin E. Cooked with a bit of fat, those antioxidants are more available to the body.

Other foods with carotenes also may offer more nutrients cooked. Examples are carrots, red and green peppers, kale, spinach, and broccoli. Some of their phytochemicals may be better absorbed by the body after being cooked.

Other foods have more antioxidants when raw. In jam made of berries, for example, antioxidant levels were lower than in the raw, unprocessed berries.

Fresh or frozen, blueberries, blackberries, raspberries, strawberries and cranberries are among the top fruit sources of antioxidants.

Nuts, seeds and grains

Along with fruits and vegetables, nuts, seeds and grains add antioxidants to the diet. Whole grains, nuts and seeds are a source for selenium, vitamin E and antioxidant phytochemicals.

Unsalted nuts and seeds have protein and fats in addition to other phytochemicals. They are a nutrient dense food.

Nut and seed oils also may help people balance their healthy fat intake. Walnuts and pecans are some of the top nuts for antioxidant content. Not crazy about nuts? Try sunflower seeds.

And don't forget those grains. When made into flour, buckwheat, millet and barley seem to hold on to their phytochemicals best.

Antioxidants add up

Overall, antioxidants from foods taken in over a long period of time seem to support health. Individual antioxidants taken as supplements have less scientific support.

When it comes to adding antioxidants to the diet, no one food or food group can do it all. The best bet is to get a variety of fruits, vegetables, nuts and whole grains into the diet.

Adding foods with different colors can help meet that goal. A food's color hints at its antioxidants. Red, orange, yellow, green, and even blue or black fruits and vegetables provide different antioxidants.

Other things in the diet, such as tea, coffee and some fruit juices also have antioxidants. Some dark chocolate may have antioxidants as well, but it depends on the cocoa contents.

And it can be helpful to make sure to get some antioxidants every day. For example, vitamin C isn't stored in the body. So eating food with that vitamin every day can help make sure the body has enough.

• Antioxidants and health. National Center for Complementary and Integrative Medicine. https://nccih.nih.gov/health/antioxidants/introduction.htm. Accessed March 11, 2024.
• Antioxidants and cancer prevention. National Cancer Institute. https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/antioxidants-fact-sheet. Accessed March 11, 2024.
• Duyff RL. Vitamins and minerals. In: Academy of Nutrition and Dietetics Complete Food and Nutrition Guide. 5th ed. Houghton Mifflin Harcourt; 2017.
• Aune D, et al. Dietary intake and blood concentrations of antioxidants and the risk of cardiovascular disease, total cancer, and all-cause mortality: A systematic review and dose-response meta-analysis of prospective studies. American Journal of Clinical Nutrition. 2018; doi:10.1093/ajcn/nqy097.
• Carlsen MH, et al. The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutrition Journal. 2010; doi:10.1186/1475-2891-9-3.
• Zeratsky KA (expert opinion). Mayo Clinic. March 11, 2024.
• Izquierdo-Vega JA, et al. Evidence of some natural products with antigenotoxic effects. Part 1: Fruits and polysaccharides. Nutrients. 2017; doi:10.3390/nu9020102.
• Lopez-Romero D, et al. Evidence of some natural products with antigenotoxic effects. Part 2: Plants, vegetables, and natural resin. Nutrients. 2018; doi:10.3390/nu10121954.
• Rusu ME, et al. Health benefits of nut consumption in middle-aged and elderly population. Antioxidants (Basel). 2019; doi:10.3390/antiox8080302.
• Artichoke. Natural Medicines. https://naturalmedicines.therapeuticresearch.com. Accessed Feb. 14, 2024.
• Neri L. Antioxidant activity in frozen plant foods: Effect of cryoprotectants, freezing process and frozen storage. Foods. 2020; doi:10.3390/foods9121886.
• 2020-2025 Dietary Guidelines for Americans. U.S. Department of Health and Human Services and U.S. Department of Agriculture. https://www.dietaryguidelines.gov. Accessed Feb. 13, 2024.

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Plant-Based Diet Twist Can Double Your Ability to Lose Weight: Stanford Study

Bonus: Research shows this style of eating can help you save $500 a year too!

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Millions are buzzing about Netflix’s battle-of-the-diets docuseries You Are What You Eat: A Twin Experiment . Spoiler alert: After just eight weeks, folks put on a plants-only plan by Stanford University scientists ended up dramatically healthier than their identical twins put on a well-balanced omnivorous plan. Plants-only twins got bad cholesterol 20 points lower, cut insulin 20% more, doubled their ability to lose weight — and scans showed they became biologically younger than omnivorous siblings who had the exact same birthday and DNA.

“The results speak for themselves,” says George Washington University nutrition expert Neal Barnard, MD. “And the twins in the study were fairly healthy to begin with. People who are out of shape will often do even better.” Take Maryland makeup artist Shauné Hayes, who gradually went plant-based after a health scare. She got off multiple meds, lost 100 pounds and feels a decade younger. Keep reading to learn surprisingly easy ways to use a plant-based diet for weight loss and huge health benefits.

Plant-based eating for weight loss beats other healthy diets

For the Stanford study, twins on both diets were coached to cut added sugar and processed carbs while emphasizing veggies, fruit and whole grains. Both groups even had nutritionist-prepared meals delivered to them part of the time. So almost everyone reduced calories, improved nutrient intake and boosted well-being. The plant group simply got a much bigger boost. Why? Well, when you eat only plants, “you almost always include more of what I call ‘power foods,’” explains Dr. Barnard, whose newest book is The Power Foods Diet: The Breakthrough Plan That Traps, Tames, and Burns Calories for Easy and Permanent Weight Loss . He says that options like broccoli, berries, beans and oats “are scientifically proven to power off excess weight that causes or worsens so many modern health problems.”

Related: Melt Up to 4 Pounds in 24 Hours With This Plant-Based Diet Twist

How ‘power plants’ turn back that clock on our health

The type of plant-based eating Dr. Barnard recommends is built around his power foods, which are all whole plant foods naturally lower in fat. He says this delivers maximum nutrients per calorie and also allows folks to eat until pleasantly full while still losing excess pounds.

The flood of nutrients we get from power foods does amazing things inside us. But weight loss is equally crucial for most of us, says the doc. That’s because as we slim down, we experience biochemical changes that help prevent, improve and even reverse countless health conditions blamed on aging, everything from diabetes and high blood pressure to heart disease and cancer .

Related: How I Lost 125 Pounds and Reversed My Pre-Diabetes on the Engine 2 Diet

Why plant-based eating for weight loss works so well

Eat a whole-food, plants-only diet, and Dr. Barnard says these are the key waist-shrinking benefits you can expect:

All-natural appetite destruction 

Fiber, protein and micronutrients in whole plants fill us up and stimulate the release of hormones that make us “immediately less hungry,” says the doc. He adds that plants satiate us after significantly fewer calories than omnivore meals, so you really can eat all you need to feel full and weight still comes off. In one study led by Kevin D. Hall, PhD , test subjects who lived in an NIH lab for a month were alternately offered either all the low-fat plant foods they wanted or all the low-carb foods they wanted. During weeks when they were offered plant foods, folks ate an average of 689 fewer calories per day . “New injectable weight-loss drugs were developed to mimic this effect,” says Dr. Barnard. “The feeling is liberating.”

Effortless metabolism boost  

Because roughage in plants stimulates metabolism, “studies show that on a plant-based diet, your ability to burn calories increases about 15% for several hours after the meal,” says Dr. Barnard. He says it’s a big reason NIH reseachers found plant-based dieters burned 4.16 times more fat mass than low-carb dieters, a finding that surprised even scientists. Says Dr. Barnard: “It’s like exercise without going to the gym. You’re getting calorie burn for free.”

Calorie blocking 

Tufts University scientists have evidence that “ plant fiber traps calories in the digestive tract and pulls them out of the body before they can be absorbed — so about 100 calories a day don’t count,” says Dr. Barnard. It may not sound like much. But remember that every power food blocks calories, boosts burn and helps shrink hunger. “All three effects all at once at every meal — that’s huge,” he adds.

Here’s your official list of power foods

Options that made Dr. Barnard’s power foods list include all fruit except avocado, all veggies including potatoes, all beans and peas, tofu, tempeh, oats, corn, whole grain, cinnamon, ginger and hot pepper.

Yes, other plants definitely have benefits. But these “power plants” are best for stimulating quick health transformations. Now, you might wonder: Won’t carbs in power foods spike blood sugar? Nope. Both fiber and plant protein blunt the rise of sugar. Plus, “new research shows that low-fat, plant-based diets are the fastest way to clear out fat that gets in cells and makes it difficult for cells to burn sugar,” says Dr. Barnard. “In one study, a plant-based diet controlled blood sugar three times better than other diets.”

Ready to see how much your body will change? Start making power foods your staples today. Bonus: Dr. Barnard says research shows you’ll save $500 a year on groceries! 

Yes, your body really will feel and act younger

While other diets always seem to work best for younger folks, “we’re doing a study right now, and we’re seeing that the benefits of plants are as strong or stronger for people in their 50s, 60s, 70s and beyond,” reveals Dr. Barnard. He says it’s because plants help heal chronic conditions that make weight harder to lose as we age. “So we’re seeing diabetes improve, blood pressure and cholesterol come down, people getting off medications. So people are finally able to lose excess weight they couldn’t get rid of for decades.”

Plant based diet for weight loss success story: Shauné Hayes, 49

Shauné Hayes vividly remembers the day she woke up and couldn’t move her right arm. Rushing to the ER, she was diagnosed with bursitis, an inflammation in the cushioning around our joints. “I was 100 pounds overweight, and it was aging my body way too fast,” Shauné shares. “I also had prediabetes, high cholesterol, hypertension, arthritis, frequent heartburn and polycystic ovarian syndrome. I needed to figure out how to get healthier.”

A health coach suggested whole-food, plant-based eating. “I was raised on barbecue and Little Debbie cakes, so I doubted I could do it,” she admits. But she had fun experimenting with power-food-packed smoothies, grain bowls, even 7-layer dip. “Within two to three weeks I felt so much better, there was no question I’d keep going. My breathing, skin, mental clarity, energy and sleep got better. Weight was coming off. My blood pressure, cholesterol and A1C came down so much, my doctor couldn’t believe it.”

A big appeal of whole-plant eating? She’d been promised she could enjoy bottomless portions, even of starchy foods, and still move toward her goals. “I ate what I wanted until I was satisfied. Wrap sandwiches, soup, curry, stews. If I wanted volume, I had it. As someone who dieted for decades, to finally be eating without those restrictions — it was such a relief, a different kind of weight lifted.”

Shauné shed 50 pounds in a year, coming off multiple meds. She kept losing. All of her health problems reversed, and she’s been 100 pounds lighter for four years. “This all happened in spite of hormonal issues that slowed my metabolism. I lost faster than I ever did when I was younger. And by eating some of the meals I make, my 76-year-old mom also lost weight and lowered her cholesterol.” Shauné now works with Dr. Barnard, helping teach others about the power of power foods. Adds Shauné, 49: “As long as you have breath in your body, try eating more plants. You’ll be amazed by what is possible.”

How to use a plant based diet for weight loss

For fastest results, build meals and snacks around plants proven to enhance weight loss. That means basically all veggies, fruit, beans/peas, minimally processed whole grains (like oats, corn and brown rice) and spices. Keep servings of nuts/seeds and healthy sweetener small. Avoid oil, animal products and highly processed foods. We’ve got ideas to inspire you below. Find more at Physicians Committee for Responsible Medicine’s recipe page .

Sample breakfast: Spring berry oats

Mix ½ cup each oats, nut milk and frozen berries and 1 Tbs. any seed; chill at least two hours; enjoy with optional maple syrup

Sample lunch: Hummus sandwich

Layer fresh, roasted and/or pickled veggies and hummus (ideally oil-free) on whole grain bread; enjoy with a side of fruit

Sample dinner: Lentil Bolognese

Just warm cooked lentils with fat-free marinara; add seasoning to taste. Enjoy over any whole-grain or bean-based pasta.

Bonus recipe: Dr. Barnard’s Quickie Stir-Fry

This dish from The Power Foods Diet is weeknight-easy and so delicious

Ingredients:

• 2 Tbs. low-sodium soy sauce
• 2 Tbs. coconut sugar or other sugar
• Sriracha to taste
• 16 oz. frozen stir-fry vegetables
• 2 cups cubed tofu or thawed edamame
• 4 cups cooked brown rice

Instructions:

• Whisk together the soy sauce and sugar; set aside.
• Stir vegetables in nonstick skillet over medium heat until warm but still crisp. Stir in tofu/edamame.
• Add sauce; mix well and let heat through. Enjoy over cooked brown rice. Serves 3-4

Deal of the Day

Click through for more on the benefits of plant-based eating:

Plant-Based Protein: 6 Types and Top Benefits of Plant Protein

This Genius 50-50 Plate Hack Is Helping Women Lose Weight Effortlessly

New Science Reveals That Simply Adding Two More Servings of Veggies a Day Can Powerfully Speed Weight Loss

New Twist on Whole30 Is Helping Women Lower Cholesterol, Eliminate Pain & Lose Serious Weight

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Global Consumer Trends for Plant-Based Dairy and Meat

Plant-based dairy and plant-based meat are ubiquitous around the world. The dairy category includes plant-based milk and milk drinks, plant-based yogurt, plant-based cheese, and plant-based and vegan butter. Plant-based meat alternatives incorporate plant-based burgers, plant-based meat cuts, plant-based nuggets and finger foods, and vegan meat snacks. Global consumer trends show that consumers have different preferences and buying habits for each.

The Popular Flexitarian Diet Includes Non-Dairy and Plant-Based Meat Products   

Non-dairy products and plant-based meat products have a place in popular diets. The flexitarian diet is followed by about one-quarter of consumers globally according to consumer trends data. An even higher proportion of consumers, one-third, follow a flexitarian diet in China. About 10% of consumers around the world are vegetarian, led by two-fifths of consumers in India. About 2% are vegans, led by vegans in India and Germany.

Many Reasons for Consuming Plant-Based Non-Dairy and Meat Alternatives   

Plant-based diets often have a more healthy, natural and sustainable image. Naturalness, digestive health and protein intake are the top health-related reasons for consuming dairy alternatives and meat alternatives. However, taste and cost remain major concerns, followed by excess processing and artificial ingredients.

Non-Dairy Milk, Meat Alternatives, Ready Meals Lead Plant-Based Categories   

According to consumer trends research, non-dairy, plant-based milk is the most consumed plant-based category globally. Plant-based cheese also is popular. Plant-based milk is most popular in Latin America, Canada, India, Spain, and the UK, while plant-based butter and margarine are the most popular in France and Germany. In contrast, consumers in China and the US report eating plant-based meat the most. Consumers expect to see these products in stores since trends research shows that about half of consumers are more likely to eat plant-based meals at home compared to eating out. Other subcategories expected and enjoyed by consumers are plant-based chocolate and plant-based ice cream and frozen dessert.

Plant-Based Non-Dairy Products are Consumed Throughout the Day  

Consumer trends research shows that around one-quarter of consumers surveyed globally say that they buy plant-based dairy alternatives. People who are more likely to buy plant-based dairy alternatives include Millennials, females, and those following a vegetarian or vegan diet. Consumers 25-44 consume dairy alternatives more frequently, including plant-based milk and milk drinks more than once a week. Consumers in North America and Asia Pacific are most likely to pick up plant-based dairy alternatives on grocery trips.

Plant-based non-dairy milk and milk drinks are the most frequently consumed non-dairy alternatives, with 15% of consumers reporting having them at least once a day. The time of day for plant-based dairy varies. Plant-based non-dairy milk/non-dairy milk drinks and non-dairy spoonable/ drinkable yogurt are included most at breakfast. Non-dairy spoonable/drinkable yogurt is also commonly consumed as an afternoon snack. Plant-based cheese is popular at mealtime.

Consumer Research Supports Benefits of Plant-Based Dairy  

Consumer trends research shows that consumers want added health benefits such as protein and fiber in plant-based non-dairy products, especially plant-based milk and milk drinks, non-dairy yogurt products, and plant-based cheese. Many consumers prefer the taste and texture of non-dairy alternative milks rather than a product that mimics cows milk. Consumers also appreciate freshness. They are most familiar with and willing to buy plant-based dairy alternatives with a base of rice, almond, coconut, or oat. Despite this, consumers want better taste and flavor in plant-based dairy alternatives, along with lower prices, less sugar and fat, and more protein.

Consumers Buying Plant-Based Meat Alternatives Eat them at Least Once a Week  

Approximately one-quarter of consumers surveyed globally report buying plant-based meat alternatives when they shop and over half say they eat them at least once a week. Plant-based meat products are purchased most by vegans and vegetarians, Millennials, and consumers with a doctorate degree. Younger consumers eat meat alternatives most often, especially plant-based meat alternative snacks such as jerky and whole meat cut substitutes. Plant-based meat products are included mostly at lunch and dinner.

Consumer Trends Support Plant-Based Meat Products That are Seasoned and Fresh  

Consumers report that fresh, seasoned plant-based meat alternatives that also have health benefits and can be served every day are most attractive to them. Products that are made from a base of rice, potato, corn, bean, or peanut are most appealing. Plant-based burgers and patties are the most preferred format in India, France, Spain and North America; plant-based sausages are preferred in Germany and the UK; breaded/battered meat alternatives are most popular in Brazil and Mexico; and Indonesians like plant-based meatballs.

Globally, consumers expect plant-based meat alternatives to mimic meat in taste and texture. They also would like plant-based meat alternatives with improved taste and texture, more protein, and less fat.

What’s Next for Plant-Based Dairy and Plant-Based Meat?  

Sustainability will be a big selling point since around half of consumers globally believe plant-based products are more sustainable than regular dairy and meat. Better animal welfare is the top environmental benefit that attracts consumers to plant-based dairy alternatives and meat alternatives. Environmental claims regarding less pesticide use, less product waste, and reduced water pollution also appeal to a majority of consumers. Also, increased biodiversity is the top reason for consuming plant-based alternatives in the Asia Pacific region.

Manufacturers can grab plant-based opportunities to improve taste, boost nutritional value, and expand options for products featuring local cuisines in meal packages and ready meals for added convenience.

This article is based on our Consumer Insider report, “Charting the Path Forward: Future Horizons for Plant-Based Consumers Worldwide.” If you are interested in reading our report on global plant-based consumer trends, feel free to request a demo. You can do this by either booking a demo or using our Contact Form.

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Original research article, efficacy of using plant ingredients as partial substitute of fishmeal in formulated diet for a commercially cultured fish, labeo rohita.

• 1 Department of Fisheries, University of Rajshahi, Rajshahi, Bangladesh
• 2 Bangladesh Fisheries Research Institute, Mymensingh, Bangladesh
• 3 Department of Geology and Planning, School of Environmental Science, University of Liverpool, Liverpool, United Kingdom
• 4 Department of Fisheries and Aquaculture, University of Veterinary & Animal Sciences, Lahore, Pakistan
• 5 Department of Environmental Studies, University of California, Santa Cruz, Santa Cruz, CA, United States
• 6 Department of Zoology, College of Science, King Saud University, Riyadh, Saudi Arabia
• 7 Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Gadong, Brunei
• 8 Department of Fisheries and Marine Science, Noakhali Science and Technology University, Noakhali, Bangladesh

Reliance on fish meal can be reduced by incorporating plant-based ingredients, making aquaculture more economical, sustainable and environmental friendly. In this study, the efficacy of plant protein ingredients (PPI) such as mustard oil cake (MOC), soybean meal (SBM) and rice bran (RB) as Partial substitute of fishmeal (FM) was investigated for a commercially important fish, Labeo rohita in cages for 90 days. Three experimental diets, labeled as Diet 1, Diet 2, and Diet 3, were formulated to be isonitrogenous (with protein content ranging from 32.20 to 32.29%) and iso-caloric (with gross energy ranging from 4.12 to 4.17 kcal/g). These diets contained different proportions of PPI (45, 68, and 79%) and FM (46, 23, and 11%, respectively). Square-shaped cages with a volume of 1m 3 (1 m × 1 m × 1 m) were stocked with 40 fish/m 3 each with an average initial weight of 52.97 g in triplicates. Fish were hand-fed to apparent satiation twice daily for 7 days a week at a feeding rate of 5% in the initial month and 3% for the rest of the culture period. 50% of the caged fish was sampled monthly to monitor growth performance and at the termination of the experiment, all the fish was harvested to measure production economics performance. The results indicated improved growth performance and higher feed utilization at Diet 2, yielding significantly ( p < 0.05) higher fish production compared to Diet 3, while these parameters were insignificant with Diet 1. By replacing FM with PPI, the total feed cost compared to Diet 1 was reduced to 20.62 and 32.76% for Diet 2 and Diet 3, respectively. The replacement of 50% FM in Diet 2 also yielded a 15.61% higher total economic net return than the Diet 1 group. However, a higher inclusion rate of PPI in Diet 3 potentially reduced fish growth, with a consequent decline of 41.61% total economic net return compared to the Diet 1 group. In conclusion, the replacement of 50% FM in Diet 2 compared to Diet 1 returned a higher benefit–cost ratio (1.72) among the feeding groups. Therefore, this FM replacement experiment suggested a 50% FM replaced diet as an unconventional, cost-effective, and readily available novel protein source without compromising the inherent nutritional quality of fish and feed in the cage culture of L. rohita . The results could be widely applicable to the fast-growing approach of cage culture technology across Asia and beyond.

Introduction

The increasing trend of fish feed cost poses a challenge in intensive culture systems ( Haider et al., 2016 ; Iqbal et al., 2020a ; Bjørndal et al., 2024 ), with dietary protein being identified as the costliest component in the production of manufactured fish food. Generally, the cost of feed constitutes around 56.45–58.49% of the total production expenses in aquaculture industry ( Hossain et al., 2022 ). In specific cases, it may even escalate to 60–70% ( Khan M. A. et al., 2018 ; Khan N. et al., 2018 ; Prodhan and Khan, 2018 ; Hossain et al., 2020a , b ). This is primarily attributed to the heightened requirements for protein, contributing significantly to the overall costs. Fishmeal (FM) is widely employed as a protein source in the majority of formulated diets and is considered as the costliest component in fish diets ( Moniruzzaman and Fatema, 2022 ). Additionally, it plays a crucial role in providing essential nutrients that promote fish growth and ensure their long-term well-being ( Batool et al., 2018 ; Haider et al., 2018 ; Bjørndal et al., 2024 ). FM is well balanced with respect to essential amino acids, fatty acids and minerals, has a low carbohydrate content, and is free of anti-nutritional factors with high palatability and digestibility ( Gatlin et al., 2007 ; Bhuyain et al., 2019 ). As a result, the rapid growth of aquaculture demands for higher FM ( NRC (National Research Council), 2011 ). Small pelagic fishes such as anchovies, sardines, mackerel, capelin, and menhaden are known to contribute about 90% of produced FM worldwide ( Tacon and Metian, 2009 ). However, FM resources are finite, continuous pressure on these fish species’ natural stock due to overfishing is likely to increase the scarcity and price of FM in the near future ( Hardy, 2008 ; Savonitto et al., 2021 ). There is also acute scarcity in the supply of FM because of the equally high demand of this protein source from other animal husbandry practices and uncertainty in collecting wild trash fish, which is the primary source of FM ( Naylor et al., 2000 ). Therefore, a higher cost and fluctuating FM supply necessitate replacing FM with cheaper, alternative protein sources with acceptable amino acid composition ( Santigosa et al., 2011 ; Köprücü and Sertel, 2012 ; Al-Thobaitia et al., 2018 ). In this case, the more affordable and alternative FM replacement options could include plant protein ingredients (PPI), animal byproducts, and other novel protein feedstuffs ( Kishawy et al., 2021 ).

The effectiveness of various PPI as a partial and complete replacement of FM in aquafeeds has been investigated by several researchers ( Suprayudi et al., 2015 ; Aziza and El-Wahab, 2019 ) whereas, soybean, barley, corn, cottonseed, wheat, mustard oil cake, rice bran etc. can replace FM and are widely used in aquafeeds ( El-Saidy and Gaber, 2002 ; Gatlin et al., 2007 ; Zamal et al., 2008 , Koumi et al., 2009 , Brinker and Friedrich, 2012 ; Khan et al., 2013 ; Ibrahem and Ibrahim, 2014 ). However, the inclusion of PPI (>50%) are sometimes reported to reduce the growth performance compared to that of fish fed FM-based diets ( Collins et al., 2013 ; Yaghoubi et al., 2016 ; Turchini et al., 2019 ). Because PPI are possessing anti-nutritional factors and indigestible carbohydrates, protein digestion and absorption of amino acids are less efficient in fish ( Lall and Anderson, 2005 ). On the other hand, using only FM to the diets sometimes results in the waste of excessive protein which increases the load of nitrogen and phosphorus in the water and deteriorate the water quality in fish pond ( Hardy, 2010 ). Study shows that the partial replacement of FM by PPI can reduce Phosphorous ( Ketola and Harland, 1993 ) and Nitrogen excretion (as ammonia) by reducing protein levels ( Cheng et al., 2003 ). Therefore, additional research is needed to adequately determine the inclusion rate of PPI in the partial replacement of FM in fish diet which could be readily available, cheap and environmentally friendly ( Hernández et al., 2016 ; Hossain et al., 2021 ). Studies indicate that diets allowing for the partial or complete substitution of FM can be feasible through a meticulous formulation process ( Espe et al., 2006 ; Kousoulaki et al., 2012 ).

Labeo rohita , locally known as rohu, is a culturally and economically significant fish species in Bangladesh, playing a vital role in aquaculture. Its vigorous biology and adaptability make it a preferred species for sustainable fish farming, contributing significantly to economic livelihoods, nutritional security, and the overall resilience of local communities ( Jewel et al., 2020a ; Pervin et al., 2020 ). The significance of developing aquaculture for L. rohita with low-cost feed in Bangladesh cannot be overstated as it is one of the sustainable practices. Because, by utilizing affordable feed options, aquaculture becomes more accessible to a broader spectrum of farmers, fostering widespread participation and contributing to poverty reduction. L. rohita , being a major cultivable species in the country, ensures that the production of this fish with low-cost feed provides an affordable protein source, positively impacting the nutritional well-being of the population. Additionally, the adoption of cost-effective feed formulations reduces the overall production costs, enhancing the competitiveness and profitability of aquaculture ventures in Bangladesh ( Akter et al., 2018 ; Pervin et al., 2020 ; Jewel et al., 2023a ).

In Bangladesh, high feed costs in aquaculture industry impose a significant economic burden on rural farmers, leading to reduced profitability and limiting the accessibility of aquaculture activities. Additionally, these elevated costs can contribute to food security concerns by potentially increasing fish prices and impacting the affordability of this essential protein source for local communities.

A primary factor contributing to this is the rising expense of fish feed ingredients, particularly the cost of FM in Bangladesh. Hence, replacing fish meal with plant-based protein sources has the potential to decrease costs. Considering the availability and crude protein content, a combination of Mustard oil cake (MOC), soybean meal (SBM) and rice-bran (RB) can be a suitable replacement option for FM. It is widely prevalent and extensively utilized as a component in aquafeed across the country. Because, mustard is one of the major oilseed crops occupying 78% of the cultivated area and contributing nearly 62% of the cultivated area of the total oilseed production in Bangladesh ( Bangladesh Bureau of Statistics (BBS), 2003 ). MOC serves as a relatively good source of crude protein ( Bhuyain et al., 2019 ). Additionally, it is more cost-effective compared to other oil cakes in Bangladesh. Moreover, SBM stands out as the most frequently employed plant ingredient, boasting high protein content (approximately 48% crude protein) and a relatively stable amino acid profile ( Ye et al., 2019 ; Meng et al., 2020 ; Pervin et al., 2020 ). RB or polish, a by-product of rice, is abundantly available throughout the year in Bangladesh. Several studies also demonstrated that RB contain 13–15% protein and 11–12% lipid ( Saunders, 1990 ; Alencar and Alvarenger, 1991 ; Nyirenda et al., 2000 ) which signifies its role as a suitable ingredient to be used for FM replacer. However, research on low-cost feed development using locally available ingredients specially using PPI for L. rohita culture in Bangladesh is very limited. Hence, this study aims to (i) assess the nutritional effectiveness of MOC, SBM, and RB as a replacement for FM in fish diets, (ii) investigate the economic impact of different FM replacement levels in a cage culture system (CSS), (iii) analyze the proximate composition of harvested fish for nutritional quality assessment, and (iv) conduct an economic analysis to determine the profitability of using PPI as a FM substitute in L. rohita culture. The insights gained from the development of low-cost aquafeeds can be extended to advance sustainable aquaculture practices for various species. This not only contributes to economic empowerment and food security but also emphasizes a commitment to responsible and inclusive aquaculture practices in Bangladesh and other developing nations.

Materials and methods

Study area and installation of cages.

The experiment was conducted for 90 days, from February to May 2017, in nine experimental cages at the Department of Fisheries, University of Rajshahi, Bangladesh. A total of three ponds were used for installing these nine cages, whereas each had three cages. The cages were square-shaped, with a volume of 1 m 3 (1 m × 1 m × 1 m) and built with metallic frames fully wrapped with a nylon net of 1 cm mesh size. Cages for each treatment were landed securely at a fixed place in a well-prepared fish pond with the help of bamboo poles. The cages were arranged in one column and firmly fixed by the bamboo poles set longitudinally and vertically. The cages were kept floating in pond water, keeping about 1 m distance from the pond bottom. Fish was hand-fed with a floating feeding tray attached inside each cage, facilitating the regular feeding of fish.

Feed formulation

The feed ingredients with their percent compositions used in the experimental diet formulation and per kg feed production cost of the prepared diets are shown in Table 1 . The selected ingredients for this experiment were collected from the local market. The feed ingredients (finely ground and sieved) were weighed accordingly, thoroughly mixed with a mixture, moistened with water to form the dough, and pelletized using a manual food grinder with a diameter of 2 mm. Three diets were formulated with the selected ingredients. Three diets were prepared using the selected ingredients. Diet 1 contained 46% FM with a crude protein (CP) content of 32.29%. Additionally, the FM concentration in Diet 1 (46%) was decreased to 50 and 75% in Diet 2 (FM 23%) and Diet 3 (FM 11%), respectively. To compensate for the reduced CP in these two diets, various combinations of PPI were included. Diet 2 and 3 are containing 68 and 79% plant protein and are lower in animal-derived protein sources (FM 23 and 11% in diet 2 and 3, respectively). Finally, the prepared sinking pelleted feeds were sun-dried for 3 days and stored in airtight polythene bags at room temperature until feeding.

Table 1 . Formulation and proximate composition of experimental diets.

Experimental setup and fish sampling

A total of three ponds were used for this experimental setup. Three cages were used for one specific experimental diet. Each cage was considered as replicate and therefore, each experimental diet of each pond was consisting of three replicated cages positioned as a row. Three treatments were assigned as Diet 1 (FM 46%), Diet 2 (FM 23%), and Diet 3 (FM 11%). The fingerlings with an initial average body weight of 52.97 g were collected from local vendors and released at a stocking density of 40 fish/m 3 in each cage. Fish were hand-fed to apparent satiation twice daily (9:00 am and 4:00 pm) for 7 days a week throughout the study period. The feeding rate was 5% in the initial month and 3% for the rest of the culture period. Every day, feed given to the fish was weighed, and the uneaten pellets were removed from the feeding tray at least 2 h after the feed was given. The uneaten feed weight was estimated daily, and feed intake was calculated for each feeding group by subtraction between the weight of daily feed given and feed uneaten. Sampling (50% fish from each cage) was done monthly to monitor growth performance and to adjust the feeding ration accordingly. At the final harvest, all the fish in each cage were collected, their final growth and production were measured, and economics was calculated.

Proximate composition of diets and fish

Diets and fish muscles were analyzed to measure crude protein, lipid, moisture, ash, and carbohydrate according to the steps followed by the Association of Official Analytical Chemists ( AOAC (Association of Official Analytical Chemists), 2005 ). Ten fish were initially used for the analysis of proximate composition. Protein, lipid, moisture and ash content of the stocked fish were 11.07, 2.40, 84.60, and 1.07%, respectively. Furthermore, at final harvest, three fish were randomly selected from each feeding group, weighed, and sacrificed and the muscle tissue was collected. Crude protein was determined by the Kjeldahl method using the automatic Kjeldahl system; lipid by petroleum ether extraction using the Soxhlet method; ash by combustion at 550°C for 24 h, moisture by oven drying at 105°C for 24 h to a constant weight. A bomb calorimeter was used to determine the gross energy content of the diet. All the samples were analyzed in triplicates. The proximate composition of the formulated diets analyzed in the present study is presented in Table 1 .

Water quality monitoring

Water quality parameters viz. water temperature (WT), hydrogen ion concentration (pH), dissolved oxygen (DO), ammonia (NH 3 ), and total alkalinity (TA) were studied fortnightly between 9:00 am to 10:00 am. WT was recorded with the help of a Celsius thermometer, while pH was measured using a pH indicator paper (Lojak). However, DO, TA and NH 3 concentrations were determined with the water quality testing kit (HACH kit FF-2, United States).

Fish growth and production performances

Economic analysis, statistical analysis.

The data obtained were presented as means ± standard deviation (SD). One-way analysis of variance (ANOVA) was performed using SPSS (Statistical Package for Social Science, ver. 20.0) to determine the effect of diets in different treatments. Detected differences were compared by Duncan’s multiple range test (DMRT), considering a significance level of p < 0.05 . The percentages and ratios were analyzed using arcsine transformed data before conducting the one-way analysis of variance (ANOVA).

Growth performance evaluation

The growth performance of L. rohita fed on varying fish feeds based on FM concentrations reared in triplicate treatments is shown in Table 2 . The fish growth increment comparison based on monthly intervals is presented in Figure 1 . The growth of L. rohita varied significantly among the Diets, with Diet 2 fed group showing a significantly higher final weight (153.62 ± 2.18 g) gain in comparison with Diet 3 group (129.50 ± 6.09 g). The maximum weight gain (101.30 ± 3.02 g) in L. rohita was observed in Diet 2 group, nonetheless, showing significant difference from Diet 3 group. Similarly, a significantly ( p  < 0.05) higher SGR was observed in Diet 2 (1.20 ± 0.04% bw/day) followed by Diet 1 (1.16 ± 0.03% BW/day) and Diet 3 (0.99 ± 0.04% BW/day). However, final weight, weight gain and SGR were showing insignificant differences among the Diet 1 and Diet 2 group. Furthermore, the survival of fish did not vary significantly among the treatments.

Table 2 . Growth performance of L. rohita in different feeding groups.

Figure 1 . Final weights (g) of L. rohita in different months of the experimental trial. Diet 1 (46% FM), Diet 2 (23% FM), and Diet 3(11% FM).

Feed utilization

Feed utilization parameters examined for the experimental treatments are shown in Figure 2 . During this study, FCR was significantly lower in Diet 2 group (2.09 ± 0.06) followed by Diet 1 (2.15 ± 0.05) and Diet 3 (2.65 ± 0.06). Furthermore, the FM replacement in the different treatments significantly affected PER of fish. A considerably higher PER was recorded in Diet 2 (1.47 ± 0.05) and lower in Diet 3 (1.18 ± 0.07).

Figure 2 . Feed conversion ratio (FCR) and protein efficiency ratio (PER) of L. rohita in different feeding groups. Different superscript letter indicates significant difference. Diet 1 (46% FM), Diet 2 (23% FM), and Diet 3 (11% FM).

During the present study, the highest yield was obtained from Diet 2 group (5.84 ± 0.08 kg/m 3 /90 days), followed by the Diet 1 (5.82 ± 0.06 kg/m 3 /90 days) and Diet 3 group (4.88 ± 0.21 kg/m 3 /90 days). There was no significant difference ( p  < 0.05) between the yields of the Diet 1 and Diet 2 group, while the yield of L. rohita in Diet 3 group was significantly different from both treatments ( Figure 3 ).

Figure 3 . Yield of L. rohita in different feeding groups. Different superscript letter indicates significant difference. Diet 1 (46% FM), Diet 2 (23% FM), and Diet 3 (11% FM).

Proximate composition of fish

The final carcass composition assessment of fish fed on different feed types formulated with varying levels of FM replacement is presented in Table 3 . There were no significant differences ( p  < 0.05) between Diet 1 and Diet 2 group, while Diet 3 group was significantly different ( p  < 0.05) from Diet 1 and Diet 2 groups. The protein and lipid contents were higher in the Diet 1 group (14.45 ± 0.27 and 4.85 ± 0.04%) followed by Diet 2 (14.38 ± 0.06 and 4.78 ± 0.03%) and Diet 3 group (13.68 ± 0.02 and 4.36 ± 0.05%), respectively. However, the moisture content turned out to be significantly ( p  < 0.05) higher in Diet 3 (80.14 ± 0.25%) and lower in Diet 1 (79.13 ± 0.36). In the same pattern, the ash content was significantly higher in Diet 3 (1.48 ± 0.02%) and lower in Diet 1 (1.24 ± 0.02%). However, the carbohydrates did not vary considerably among the treatments.

Table 3 . Proximate composition of L. rohita in different feeding groups.

Economic performance evaluation

A comparison of economic returns from the fish groups treated with varying degrees of FM replacement is shown in Table 4 . The highest cost was estimated from the Diet 1 group (BDT 752.53), followed by Diet 2 (BDT 680.08) and Diet 3 group (BDT 636.72). However, significantly higher total economic return as the fish sale of Diet 2 (BDT 1167.23) followed by Diet 1 (BDT 1164.52) and Diet 3 (BDT 877.61). The total net economic return was significantly higher in Diet 2 (BDT 487.15), while the lowest was Diet 3 (BDT 240.89). Furthermore, the Diet 2 group provided a considerably higher BCR (1.72) than the other two treatments.

Table 4 . Benefit–cost analysis of L. rohita in different feeding groups after 90 days of culture period.

Water quality assessment

The mean values of water quality parameters recorded from the three experimental treatments during the study period are displayed in Table 5 . Formulation of feed based on varying replacement levels of FM did not affect the water quality of CCS, indicating no significant impact of increased plant protein on the suitability of water quality.

Table 5 . Water quality parameters in different feeding groups (Mean ± SD).

This study attempted to investigate replacing FM with PPI for L. rohita reared in CCS. Significantly higher finishing weight of fish was achieved in Diet 2 group and lower in Diet 3. Weight gain and SGR alluded to substantially higher performance in Diet 2 that declined in, Diet 3. The replacement of animal protein sources (FM) up to a certain level with plant protein sources was not detrimental, as was evident in the findings of Furuya et al. (2004) and Lin and Luo (2011) . Even a 50% replacement of FM in diets has been reported to be favorable for the overall fish growth performance ( Viola et al., 1982 ; Jahan et al., 2012 ). However, replacing 75% animal-source protein reduced fish growth in the present experiment in Diet 3. Incorporating PPI higher than the sub-optimal level might negatively affect fish growth. Although, we have not measured the level of anti-nutritional factors (ANFs) present in PPI in our study. However, we presume that the greater PPI might increase toxic components (ANFs) and imbalance the amino acid profile responsible for intestinal irritation and reduced growth ( Olvera-Novoa et al., 2002 ). This understanding corroborates the earlier outcomes by Hua and Bureau (2012) , who opposed the total replacement of FM protein with plant protein as it could be detrimental to the cultured organisms. Complete FM replacement is also reported to decrease protease activities in the intestine and hepatopancreas in Juvenile Tilapia ( Lin et al., 2010 ). Jalili et al. (2013) also found reduced digestive enzyme activities and subsequent lower growth in rainbow trout fed the diet with 75 and 100% FM replacement. In the present study, 75% replacement of FM by PPI in Diet 3 may be the reason for the reduced growth performance of L. rohita to the other treatments.

The proportion of protein and non-protein energy sources is necessary while preparing a balanced diet. An excess protein in the diet causes higher ammonia, affecting fish growth performance ( Kaushik and Medale, 1994 ). When adequate non-protein energy sources are available in the diet, it could minimize the use of protein as an energy source and enhance fish’s growth performance ( Iqbal et al., 2020b ). Carps are the most efficient exploiters of carbohydrates ( Kumar et al., 2005 ). The intrusion of carbohydrates in the form of PPI in Diet 2 could impart a protein-sparing effect that may enhance the feed utilization by fish. The protein-sparing effect of suboptimal levels of carbohydrates was also reported in silver barb by Mohanta et al. (2007) . An appropriate level of carbohydrate in the diet can reduce protein degradation and amino acid oxidation which results in improved growth ( Frick et al., 2008 ). However, several studies also reported that dietary carbohydrate beyond the optimal level can cause lower growth and feed utilization in fish ( Tan et al., 2009 ; Gao et al., 2010 ; Yu et al., 2022 ). Therefore, lower growth and feed utilization in Diet 3 group was lower despite of the higher carbohydrate level. Therefore, replacing FM in the diet did not affect fish survival. Jahan et al. (2007) found no significant difference between the treatments regarding survival rate in a partial replacement experiment of FM with SBM for the fry of Cirrhinus cirrhosus . Replacement of FM in fish diets can significantly affect the total fish yield, whereas the higher production was recorded in Diet 2 group with a 50% replacement of FM. However, the higher inclusion rate of PPI in Diet 3 caused a significant reduction in the total yield.

The FCR decreased in the fish of Diet 2 compared to the Diet 1 fish and increased significantly in Diet 3. The earlier investigations have argued that low FCR indicates higher feed utilization efficiency, balancing bioavailability and partitioning dietary nutrients toward growth ( Angelidis et al., 2005 ). Zamal et al. (2009) reported a high-energy diet produced a lower FCR and higher nutrient retention in the fish body. Therefore, 50% FM replacement in feed increased the feed efficiency, but it decreased in growing proportion for PPI in the feed (Diet 3). The present findings are supported by the conclusions of Devi et al. (1999) , who reported relatively better (lower) FCR in L. rohita fingerlings fed on a diet including 20% SBM.

Similarly, they found a higher FCR while increasing the proportion of SBM up to 40 and 60%. PER is related to the dietary protein intake and its conversion into fish weight gain ( Koumi et al., 2009 ). The fish fed on varying levels of a FM replacement diet showed a significantly higher PER in Diet 2 and lower in Diet 3. The lower PER obtained in Diet 3 might be due to the imbalance of amino acid profile as affected by the higher inclusion rate of PPI, which was also supported by Espe et al. (2008) . Plant protein sources generally have lower biological value and palatability properties ( Estevez et al., 2011 ), which may be responsible for lower feed utilization in Diet 3 group. However, a balanced proportion of FM and PPI in Diet 2 might provide essential amino acids and increase fish feed utilization. The study by Espe et al. (2006 , 2010) and Estevez et al. (2011) also showed that the palatability of a plant protein-based diet could be enhanced by adding essential amino acids and other animal proteins protein sources.

Replacement of 50 and 75% FM in Diet 2 and Diet 3 resulted in a 20.62 and 32.76% reduction in total feed cost, while 15.61% higher net economic return was obtained from Diet 2 compared to the Diet 1 group. A study conducted by Khan et al. (2013) reported that 24% of feed formulation costs could be reduced by the replacement of FM with rice polish (up to 20%) and MOC (up to 22%) without changing the nutritional quality in an experiment on Oreochromis niloticus . However, a higher inclusion rate of PPI in Diet 3 reduced the fish growth and subsequent reduction of 41.61% net economic return compared to Diet 1 in the present study. Finally, the replacement of 50% FM provided a higher BCR (1.72) compared to the other treatments. Apart from fish feed types, various environmental factors such as water temperature, turbidity, pH and ammonia play a crucial role in the CSS that must be considered ( Ara et al., 2020 , 2023 ; Jewel et al., 2020b , 2023b ; Bashak et al., 2021 ).

Replacement of fish meal with FM at different levels significantly impacted the muscle protein and lipid content of L. rohita . Fish in Diet 2 retained a higher protein level compared to other treatments. However, lipid content was reduced considerably in Diet 3 compared to the Diet 1 group, potentially due to a higher inclusion rate of PPI in the diet. A similar observation by Devi et al. (1999) has reported higher protein and lower lipid levels in the muscle tissues of L. rohita fingerlings fed with a plant protein-based diet (SBM-based rations) compared to the Diet 1 group (0% SBM). Contradictory results were observed by Khan M. A. et al. (2018) and Khan N. et al. (2018) . They reported that incorporating plant protein by replacing FM did not significantly affect the whole-body composition of Indian major carps, Catla catla , L. rohita and C. cirrhosus. A significant effect of FM replacement on the proximate composition of fish during the present study may be linked to anti-nutritional factors in PPI, although several studies reported the influence of FM replacement with plant protein sources on the proximate composition of fish ( Olli and Krogdahl, 1995 ; Elangovan and Shim, 2000 ).

The present study affirmed that 50% replacement of FM by PPI could be economically efficient in reducing the feed formulation cost by approximately 20.45% without changing the proximate composition (nutritional quality) of L. rohita reared in the CSS. A replacement of 50% FM with PPI also increased the total net return by 15.61%, which was the most economical among all the experimental treatments for the cage culture of L. rohita in ponds. This study can also be extended to other leading aquaculture fish species to test the potential of using PPI as an alternative protein source of FM to reduce the increasing pressure on FM demand. This approach aligns with sustainable practices by promoting environmentally friendly alternatives and encouraging knowledge-sharing among practitioners. Therefore, the development of aquaculture for L. rohita using low-cost feed will not only supports economic empowerment and food security but also embodies a commitment to responsible and inclusive aquaculture practices in Bangladesh or other developing nations. However, in the current investigation, ANFs of PPI were not examined, which may restrict the acceptability of the designed diet. As a result, the current study recommends that the PPI’s ANFs be examined before to their usage in feed composition.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

Ethics statement

The animal study was approved by University of Rajshahi, Bangladesh. The study was conducted in accordance with the local legislation and institutional requirements.

Author contributions

SA: Data curation, Writing – original draft. AH: Data curation, Writing – original draft. A-AS: Supervision, Writing – review & editing. UA: Software, Writing – review & editing. SI: Software, Writing – review & editing. PS: Data curation, Funding acquisition, Writing – review & editing. BP: Writing – review & editing. TA: Writing – review & editing. MH: Resources, Software, Writing – review & editing.

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This study was supported by Researchers Supporting Project Number (RSP2024R144), King Saud University, Riyadh, Saudi Arabia.

Acknowledgments

The authors are grateful for financial support from the National Science and Technology Fellowship from the Ministry of Science and Technology, The Government of People’s Republic of Bangladesh. The authors would like to extend their sincere appreciation to the Researchers Supporting Project Number (RSP2024R144), King Saud University, Riyadh, Saudi Arabia.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

Publisher’s note

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Keywords: feed formulation, growth metrics, proximate chemical composition, dietary protein sources, Indian major carps

Citation: Akter S, Haque MA, Sarker MA-A, Atique U, Iqbal S, Sarker PK, Paray BA, Arai T and Hossain MB (2024) Efficacy of using plant ingredients as partial substitute of fishmeal in formulated diet for a commercially cultured fish, Labeo rohita . Front. Sustain. Food Syst . 8:1376112. doi: 10.3389/fsufs.2024.1376112

Received: 24 January 2024; Accepted: 14 March 2024; Published: 04 April 2024.

Reviewed by:

Copyright © 2024 Akter, Haque, Sarker, Atique, Iqbal, Sarker, Paray, Arai and Hossain. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: M. Belal Hossain, [email protected] ; Pallab Kumer Sarker, [email protected]

This article is part of the Research Topic

Sustainable Aquaculture Production for Improved Food Security

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The Impact of Plant-Based Dietary Patterns on Cancer-Related Outcomes: A Rapid Review and Meta-Analysis

Esther molina-montes.

1 Department of Nutrition and Food Science, University of Granada, 18014 Granada, Spain; se.rgu@vneleb

2 Institute of Nutrition and Food Technology (INYTA) ‘José Mataix’, Biomedical Research Centre, University of Granada, Avenida del Conocimiento s/n, E-18071 Granada, Spain

3 Instituto de Investigación Biosanitaria ibs.GRANADA, 18012 Granada, Spain; [email protected]

Elena Salamanca-Fernández

4 CIBER of Epidemiology and Public Health (CIBERESP), 28029 Madrid, Spain

5 Andalusian School of Public Health (EASP), 18014 Granada, Spain

Belén Garcia-Villanova

Maria josé sánchez.

6 Department of Preventive Medicine and Public Health, University of Granada, 18016 Granada, Spain

Long-term cancer survivors represent a sizeable portion of the population. Plant-based foods may enhance the prevention of cancer-related outcomes in these patients. We aimed to synthesize the current evidence regarding the impact of plant-based dietary patterns (PBDPs) on cancer-related outcomes in the general population and in cancer survivors. Considered outcomes included overall cancer mortality, cancer-specific mortality, and cancer recurrence. A rapid review was conducted, whereby 2234 original articles related to the topic were identified via Pubmed/Medline. We selected 26 articles, which were classified into studies on PBDPs and cancer outcomes at pre-diagnosis: vegan/vegetarian diet ( N = 5), provegetarian diet ( N = 2), Mediterranean diet ( N = 13), and studies considering the same at post-diagnosis ( N = 6). Pooled estimates of the associations between the aforementioned PBDPs and the different cancer outcomes were obtained by applying random effects meta-analysis. The few studies available on the vegetarian diet failed to support its prevention potential against overall cancer mortality when compared with a non-vegetarian diet (e.g., pooled hazard ratio (HR) = 0.97; 95% confidence interval (CI): 0.88–1.06). The insufficient number of studies evaluating provegetarian index scores in relation to cancer mortality did not permit a comprehensive assessment of this association. The association between adherence to the Mediterranean diet and cancer mortality reached statistical significance (e.g., pooled HR = 0.84; 95% CI: 0.79–0.89). However, no study considered the influence of prognostic factors on the associations. In contrast, post-diagnostic studies accounted for prognostic factors when assessing the chemoprevention potential of PBDPs, but also were inconclusive due to the limited number of studies on well-defined plant-based diets. Thus, whether plant-based diets before or after a cancer diagnosis prevent negative cancer-related outcomes needs to be researched further, in order to define dietary guidelines for cancer survivors.

1. Introduction

The latest global cancer statistics have reported that there were 17.0 million new cases of cancer and 9.5 million cancer-related deaths (excluding non-melanoma skin cancer) in 2018 [ 1 ]. It is estimated that 43.8 million cancer patients who survived the disease for five years or more were alive in 2018, with lung, breast, colorectal, prostate, and gastric cancer contributing more prominently to this number [ 2 , 3 ]. Data from Europe (EU-28) are also impressive, with more than 12.1 million prevalent cancer patients in 2018 [ 3 ]. Parallel to the increase of the number of new cancer patients over the past decades, the proportion of cancer survivors has also grown. Survival rates for cancer have increased steadily for patients diagnosed with cancer from 1999 to 2007 [ 4 ]. This increased survival may be partially attributed to improved diagnosis and treatments, better access to high-quality services and earlier diagnosis [ 5 ]. However, several factors can lead to worse cancer prognosis, among which unhealthy dietary choices warrant special consideration [ 6 ].

Plant-based food (fruits, vegetables, cereals, nuts and seeds, legumes, and vegetable oils) are the main source of fiber and other bioactive compounds in the diet [ 7 ]. Particularly, plant bioactives including fiber, sulfur compounds, carotenoids, and polyphenols, present in foods such as cruciferous and allium vegetables, tomatoes, green tea, and whole grain cereal, have well-known anticarcinogenic properties [ 7 ]. Plant-based foods are therefore likely to exert anti-inflammatory and anti-oxidative effects against the development of cancer [ 7 ]. Thus, whereas an unhealthy diet is an established risk factor for several cancer types, eating plant-based foods to achieve a healthful diet has been associated with a reduced cancer risk according to the latest report on diet and cancer, released by the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) [ 8 ].

A considerable number of studies examined the association between individual nutrients or foods and cancer mortality [ 9 , 10 ]. Most of these studies have focused on associations between pre-diagnosis dietary intake and cancer-related outcomes, while only a few studies have assessed how post-diagnosis dietary intake affects these outcomes [ 11 ]. Moreover, nearly all have focused on overall cancer mortality, whereas studies on cancer-specific mortality are scarce [ 11 , 12 , 13 , 14 ]. In addition to the above, findings from these studies are far from conclusive. For example, inconsistent associations were reported between fruit and vegetable consumption and cancer mortality in a meta-analysis of sixteen prospective studies [ 15 ]. For other plant-based foods, including nuts [ 16 ] and legumes [ 9 ], strong associations with cancer mortality have been observed. In contrast, olive oil consumption was not found to be associated with cancer mortality in several studies [ 17 , 18 ]. Therefore, until now, there is no sufficient evidence to recommend dietary factors for cancer mortality prevention.

Considering, the overall diet (i.e., the dietary pattern) is more appropriate in view of the complex nature of the diet, and the interrelation between its constituents (foods and nutrients) [ 19 ]. Dietary patterns can be assessed using the conceptual framework of a dietary pattern (a priori), or empirically (a posteriori), and allow to establish more robust associations than when considering nutrients or foods on an individual basis [ 20 ]. It is also of great importance that dietary patterns, especially a priori dietary patterns, are more suitable to derive dietary guidelines for the prevention of cancer [ 8 , 21 ]. However, not much attention has been paid to the influence of diet as a whole on cancer mortality outcomes. So far, the WCRF/AICR cancer prevention guidelines establish the same recommendations for cancer survivors as for the general population. Adherence to these guidelines by means of the WCRF/AICR 2007 score has been associated with a lower cancer mortality risk in a meta-analysis combining only three studies on this association [ 14 ].

Thus, whether specific dietary guidelines reduce cancer mortality risk in the population (before the diagnosis of cancer) or in cancer survivors (from post-diagnosis) remains unclear. Dietary guidelines accounting for the holistic effects of plant-based foods within a healthy diet for preventing cancer mortality are crucial in this regard. Their effects have been thoroughly examined for cancer incidence [ 13 , 22 ], but not with respect to cancer mortality. Hence, the aim of this review was to synthesize the current evidence regarding cancer mortality. For the purpose of this review, plant-based dietary patterns (PBDPs) were deemed to be the vegetarian diet (VD) in all its variations and the Mediterranean diet (MD). For the latter, we focused on a priori-derived MD indexes (e.g., the MD score, the alternate MD index (aMED), and others, in their various versions), whereas empirically derived a posteriori patterns were discarded. Furthermore, we distinguished between pre-diagnostic and post-diagnostic effects of PBDPs on cancer outcomes including overall cancer mortality, cancer-specific mortality, and cancer recurrence.

2. Materials and Methods

A rapid review methodology was chosen to conduct the review in a timely manner, following a pre-established protocol for systematic reviews (with the exception of several steps that were omitted to speed up the process, such as methodological quality assessment), and according to the general methodology of the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines [ 23 , 24 , 25 ]. Whenever possible, results extracted from the selected studies were pooled in a meta-analysis. The steps are described in more detail below.

2.1. Search Strategy

Leading electronic databases (Medline via PubMed) were searched from 1999 (no studies were available before) until 20 April 2020. The search strategy used (with a combination of Mesh terms, keywords, and operators) is detailed in Appendix A . The flow diagram illustrating the process of identifying and selecting studies is shown in Appendix B .

2.2. Study Eligibility Criteria

The review included all original studies in humans that provided data on cancer mortality or survival in relation to PBDPs. These studies were intervention studies, cohort studies, and case-control studies. Systematic reviews or meta-analyses were not eligible, but they were included in the search to further retrieve original studies on the topic by manual search. The most updated reviews were selected as references to encompass all the available studies [ 11 , 26 , 27 , 28 ]. Studies that were published thereafter and those studies not included in these previous reviews were included too.

With reference to the outcomes, we considered studies the primary outcome of which was overall and/or cancer-specific mortality, and studies reporting results on other related outcomes such as recurrence and progression of the disease. Cancer survivors did not include survivors of cervical lesions or adenomas in the colon since these are considered benign or non-malignant lesions according to common histological classification of tumors. In addition, eligible studies were those evaluating dietary patterns by questionnaire assessment.

PBDPs were defined as: (i) a diet excluding meat and meat products, flesh from any animal, and seafood, or all foods of animal origin, in the strictest sense (vegetarian and vegan diet, respectively); and (ii) a diet featuring a higher consumption of fruits, vegetables, legumes, and nuts over foods of animal origin. We considered the vegetarian diet and Mediterranean diet (MD) as plant-based dietary models. For the former, vegetarian population studies or studies that ascertained compliance with the vegetarian diet standards were eligible. To establish the latter, only a priori-derived MD indexes were included due to their high translational capacity into dietary prevention guidelines. In the light of the different adaptations that have been applied to the first MD score (MDS) proposed by Trichopoulou et al. [ 29 , 30 ], no restrictions were applied to these indexes.

All possible comparisons between vegetarians, vegans (or both combined) with respect to omnivores or different combinations of vegetarianism (e.g., lacto-ovo vegetarians) were considered. We also considered studies that established comparisons by levels of adherence to PBDPs. Furthermore, studies assessing the association between PBDPs and cancer mortality both before and after cancer diagnosis were included.

Studies conducted in children and adolescents (aged <18 years) were excluded, as were those not reporting any risk estimate (odd ratio (OR), relative risk (RR), or hazard ratio (HR) and the corresponding 95% confidence interval (CI)) on the association between dietary patterns and the aforementioned cancer-related outcomes. Studies written in languages other than English or Spanish were also excluded.

2.3. Data Collection and Analysis

Selection of studies.

Studies were first screened by title and abstract by two reviewers (E.M.M. and E.S.F.) and the final study selection was performed based on a full text review. When there were several articles reporting results based on the same study population, we included the study reporting the most updated data. Any discrepancies were resolved by consulting a third reviewer (M.J.S.).

2.4. Data Extraction and Management

Data extraction was performed by three reviewers (E.M.M., E.S.F., and B.G.V.) using a predefined standardized form to collect information on: (a) study characteristics: authors and year(s), study description and design, country, study population characteristics with regard to sample size, gender, and age; (b) the assessment methods used to collect information on diet (questionnaires and tools) and cancer-related outcomes (cancer registry or medical records data), also distinguishing between pre- and post-diagnosis association studies; (c) the measured outcomes: overall cancer mortality, cancer-specific mortality, and cancer recurrence; (d) the PBDPs under consideration (vegetarian, Mediterranean, and their variations), type (population-based or a priori), and the comparison groups (e.g., high vs. low adherence or vegetarians/vegans vs. omnivores); and (e) the reported results: measures of effect size (OR, HR, and RR, with 95% CI) and confounding variables considered for adjustment.

2.5. Presentation of Results

The results of all studies were presented in tabular format and summarized narratively by type of dietary pattern and cancer-related outcome. To summarize these studies, we described their results and risk estimates adjusted for all potential confounders. When possible, these results were pooled in meta-analyses.

2.6. Meta-Analysis

We calculated the summary estimates (from log HR/RRs in cohort studies, for dichotomous outcomes and comparisons between exposure groups) and corresponding 95% CIs when at least two studies reported results on the same outcome, using random effects models to account for possible heterogeneity between studies [ 31 ].

The Cochran Q test and I2 test statistic (assuming heterogeneity if I2 > 50%) were used to assess heterogeneity between studies. Publication bias was assessed by Egger’s test and visual inspection of the funnel plots [ 32 , 33 ]. A p-value of < 0.05 was deemed as statistically significant. The “metafor” package in R version 3.6.3 (R software) was used for these analyses.

A total of 2234 publications was identified. In addition, we considered the most up-to-date reviews addressing the association between dietary patterns and cancer mortality [ 11 , 12 , 13 , 14 ]. These reviews added 25 studies, not previously retrieved. Of these, 930 were excluded in the first step to retain original articles published from 1999. Then, 1256 studies were excluded on the basis of title and abstract, and 73 publications were reviewed using full text. Forty-seven publications were excluded for not fulfilling the inclusion criteria (no cancer related outcomes = 19; not about dietary patterns but single nutrient/food studies = 14; not an original study = 1; a posteriori indexes = 5; a priori but not MD = 8). Thus, 26 studies were included in this review: 5 VD-like studies [ 34 , 35 , 36 , 37 , 38 ], 12 MD-like studies [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ], 2 provegetarian diet studies [ 52 , 53 ], and 6 post-diagnosis studies [ 54 , 55 , 56 , 57 , 58 , 59 ]. The study by Key et al. was not included because no risk ratios on cancer mortality were reported [ 60 ]. Results are presented in the following sections.

3.1. Vegetarian and Vegan Diet

With reference to cancer mortality, characteristics of the studies evaluating VDs (vs. nonvegetarians) and cancer mortality are shown in Table 1 . These studies were based on large cohorts of known vegetarians and vegans also including nonvegetarians/nonvegans, who were followed-up for different outcomes including cancer mortality. Some of these cohorts were the Adventist Mortality Study, the Adventist Health Studies, the Oxford and Heidelberg Vegetarian Studies, the European Prospective Investigation into Cancer and Nutrition (EPIC) Oxford Vegetarian Study, and the Health Food Shoppers Study, which were combined in some of the selected publications [ 35 , 38 , 55 ]. Some studies based the VD assessment on questions regarding whether the participants followed a VD or not (e.g., Health Food Shoppers study); on the reported consumption of meat or fish using close-ended questions (e.g., Heidelberg study); or on dietary questionnaires aiming to identify non-consumers of meat or fish (e.g., the Adventist Health Study). The studies by Orlich et al. and Key et al. [ 37 , 61 ] were based on two different arms of the Adventist Health Study. Both were included to account for overall and cancer-specific (colorectal) mortality. All studies assessed the association between vegetarian eating habits and cancer mortality before cancer diagnosis (all excluded prevalent cancer cases at recruitment), and all assessed cancer mortality and cause-specific mortality using national mortality registry data (death certificates).

Characteristics of the studies evaluating VD (vs. nonvegetarian diet) and cancer mortality including cause-specific cancer mortality.

RR = relative ratio; CI = confidence interval; F = females; M = males; FFQ = food frequency questionnaire; 24-HR = 24 h recall; CRC = colorectal cancer; NA = not available; n = number of events; N = total population (or vegetarians). Adjustments: 1: sex; 2: sge; 3: smoking; 4: physical activity; 5: alcohol intake; 6: education; 7: body mass index (BMI); 8: race; 9: income; 10: marital status; 11: region; 12: sleep; 13: hormone replacement therapy (HRT) use; 14: history of peptic ulcer and inflammatory bowel disease (IBD); 15: family history of colorectal cancer; 16: energy; 17: treatment for diabetes; 18: aspirin/statins; 19: supplemental Ca/vitamin D; 20: fiber; 21: colonoscopy; 22: supplements; 23: study/method of recruitment; 24: parity; 25: oral contraceptive use; 26: HRT use; 27: diabetes; 28: blood pressure.

The study by Key et al. [ 34 ] compared death rates between vegetarians and nonvegetarians and showed significant heterogeneity between the five included cohorts. This heterogeneity was probably driven by the fact that the studied populations differed with regard to socio-demographic factors and definitions of the vegetarian population groups. Risk estimates were adjusted for age, sex, and smoking, despite the fact that smoking was not collected in some of the included cohorts. Unreliable associations were reported by duration of vegetarianism due to the limited sample size. In addition, participants were asked whether they considered themselves vegetarians, but no further dietary information was collected. Two of the cohorts (the Oxford Vegetarian and Health Food Shoppers) were included in the article by Appleby et al. [ 35 ]. Later on, Appleby et al. [ 38 ] compared vegetarian vs. nonvegetarian dietary habits in relation to cancer mortality (overall and by cancer type) in some of these previous cohorts (the Oxford Vegetarian and EPIC Oxford Study from the UK). This study also combined vegans and vegetarians in the analyses but considered as a reference group, regular meat eaters (intake >5/week). Importantly, low meat eaters (intake <5/week) and fish eaters (i.e., pesco-vegetarians) were considered in separate categories. The latter study also adjusted for every possible confounding variable related to medical history and lifestyle habits. The studies by Orlich [ 37 , 61 ] based the assessment of vegetarian diet on the dietary information collected with a validated food frequency questionnaire (FFQ) among 73,308 participants of the Adventist Health Cohort. Using this dietary data, the authors were able to classify participants into vegans, lacto-ovo vegetarians, pesco-vegetarians, semi-vegetarians, and nonvegetarians, according to the frequency of intake of particular animal foods (eggs/dairy <1/month, fish >1/month, meats <1/week, and meats >1/week, respectively). This study was, indeed, one of the few reporting risks associated with cancer mortality comparing different types of vegetarians to nonvegetarians, as well as all kinds of vegetarians vs. nonvegetarians. No significant associations were reported with respect to cancer mortality in any of these subgroups. Finally, the study by Chang-Claude et al. [ 36 ], included 1225 vegetarians and 679 health-conscious nonvegetarians from Germany, who provided dietary information on usual frequency of consumption of plant-based foods, milk, eggs, fish, meat, and processed meat. Mortality ratios were compared for vegans and vegetarians, while RRs associated with cancer mortality and adjusted for relevant confounders were reported for vegetarians and vegans combined vs. nonvegetarians. None of these studies considered the influence of cancer treatment or other prognostic factors on the associations.

Pooled estimates of effect sizes and 95% CIs for cancer mortality comparing vegetarians vs. non-vegetarians are shown in Figure 1 and described below. Whenever possible, we removed overlapping cohorts between the studies (e.g., those included in Key et al. (1999) and Appleby (2002) [ 34 , 35 ]). There was no evidence for publication bias according to funnel plots and Egger tests.

Meta-analysis under random-effects model (REM) with regard to vegetarian diet (VD) (vs. nonvegetarian diet) by subgroups of overall cancer mortality and cause-specific mortality. Q and I 2 statistics are indicated for each subgroup analysis together with the pooled estimate (rhombus).

3.1.1. Overall Cancer Mortality

Overall cancer mortality was evaluated in four articles [ 35 , 36 , 37 , 38 ], with one article reporting estimates for two different cohorts [ 35 ]. The articles by Appleby [ 35 , 38 ] combined the study populations of the Oxford Vegetarian Study, the Health Food Shoppers Study, and the EPIC Oxford Vegetarian Study. While there seemed to be population overlap in the Oxford Vegetarian Study between the articles [ 35 , 38 ], it was not possible to retrieve separate risk estimates by study populations. The overall analysis was based on 139,174 participants and 1661 cancer mortality events. The mean age of study participants varied greatly between the studies (from 43 to 58 years), as well as the level of confounding adjustment: from minimal by age, sex, and smoking adjustment [ 35 ] to full adjustments [ 36 , 37 , 38 ]. Pooled estimates showed that VD (vs. nonvegetarian) was not significantly associated with overall cancer mortality (RR = 0.97; 95% CI: 0.88–1.06). There was no significant heterogeneity between the studies (I 2 = 30%, p = 0.24).

3.1.2. Breast Cancer Mortality

There were three articles on the association between VD and breast cancer mortality [ 34 , 35 , 38 ], which together analyzed the association within six cohorts. Potential population overlap between the Oxford Vegetarian Study cohorts could not be resolved. After pooling risk estimates, based on 228 breast cancer events among 83,985 participants, a non-significant association was observed between VD (vs. nonvegetarian) and breast cancer mortality (RR = 0.99; 95% CI: 0.67–1.44). Heterogeneity tended to be significant and became less apparent after exclusion of the Heidelberg Study included in Key et al. [ 34 ]. The association remained, however, nonsignificant (data not shown).

3.1.3. Colorectal Cancer Mortality

Three studies including six cohorts reporting results for 279 colorectal cancer events among 83,985 participants, evaluated the association between VD and colorectal cancer mortality [ 34 , 35 , 38 , 61 ]. Vegetarian diet (vs. nonvegetarian) compliance was not significantly associated with colorectal cancer mortality after pooling risk estimates of these studies (RR = 1.03; 95% CI: 0.84–1.26). There was no heterogeneity among the studies (I 2 = 0%, p = 0.54).

3.1.4. Cancer Mortality for Other Cancer Types

Prostate and lung cancer mortality was evaluated in two [ 34 , 35 ] and three [ 34 , 35 , 38 ] articles, respectively. Both showed nonsignificant associations in pooled analyses. Gastric cancer mortality was also evaluated in two of the cohorts included in the study by Key et al. [ 34 ], but no consistent associations were reported. For other cause-specific cancer mortality, only pancreas, ovary, and lymphatic/hematopoietic cancers were evaluated in relation to VD in the study by Appleby et al. [ 38 ]. Interestingly, there was a significant inverse association of VD (vs. nonvegetarian) with pancreas cancer mortality (RR = 0.44; 95% CI: 0.26–0.76) and lymphatic/hematopoietic cancer mortality (RR = 0.47; 95% CI: 0.30–0.73), but a nonsignificant association with ovarian cancer mortality. Low meat eaters vs. regular meat eaters were also found to have lower pancreatic cancer mortality risk (RR = 0.54; 95% CI: 0.35–0.85) in this study.

3.2. Provegetarian Diets

Our literature search retrieved two studies on the association between provegetarian diets and cancer mortality [ 52 , 53 ]. Characteristics of these studies are shown in Table 2 .

Characteristics of the studies evaluating provegetarian diets and cancer mortality including cause-specific cancer mortality.

F = females; M = males; FFQ = food frequency questionnaire; 24-HR = 24 h recall; CRC = colorectal cancer; NA = not available; n = number of events; N = total population. Adjustments: 1: sex; 2: age; 3: smoking; 4: physical activity; 5: alcohol intake; 6: education; 7: BMI; 8: race; 9: energy intake; 10: use of aspirin and multivitamins; 11: family history of medical conditions; 12: menopausal status; 13: HRT use; 14: weight change; 15: medical history; 16: use of medication for hypertension and hypercholesterolemia.

In the first study [ 52 ], conducted with 7216 elderly participants (mean age = 67 years) of the Spanish PREDIMED (Prevención con Dieta Mediterránea) study, the authors assessed five levels of adherence to a provegetarian diet score by considering fruits, vegetables, nuts, cereals, legumes, olive oil, and potatoes as positive components, and animal fats, eggs, fish, dairy products, and meats or meat products as negative components. As the authors showed, this score was not correlated with the traditional MD score, supporting that both scores capture different dietary dimensions of a plant-based diet. This study used dietary data obtained through a validated 137-item FFQ, which was administered yearly during the follow-up. The outcome (death) was assessed through the review of clinical records and linkage to the mortality registries. During 4.8 years of follow-up, there were 130 cancer deaths documented, evenly distributed across the levels of adherence to the score. As a consequence, a nonsignificant association with cancer mortality was observed (HR high vs. very low score = 0.66; 95% CI: 0.35–1.24). The estimated HRs were adjusted for age, gender, smoking, physical activity, educational level, energy intake, and alcohol consumption. Additional adjustment for anthropometric measures and medical history, or accounting for variations in dietary habits over time, did not change the interpretation of the results.

Three different plant-based dietary indexes were evaluated in relation to cancer mortality in the study by Baden et al. [ 53 ]. The purpose of this study was to examine whether changes in adherence to these scores in 12 years were related to cancer mortality. A total of 75,314 men and women (mean age = 63 years) from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS) were followed-up for cancer deaths ( N = 4263). Dietary data were collected every four years with a validated semi-quantitative FFQ. The authors proposed an overall (standard) provegetarian plant-based score, as well as healthier and unhealthier versions of this score. These scores were based on the premise that plant-based foods have different diet quality, with foods such as fruit juices, refined grains, potatoes, sugar-sweetened beverages, and sweets and desserts presumed to be less healthy; whereas whole grains, fruits, vegetables, nuts, legumes, vegetable oils, tea, and coffee are considered the opposite. All plant-based foods were scored positively, while all other foods scored negatively. The change in adherence to the scores (at 8, 12, and 16 years) was evaluated in relation to risk of cancer death. Cancer deaths in the cohorts were identified through mortality registries and/or reported by the participant’s relatives. The authors found that an increase in adherence to the provegetarian standard score (vs. stable adherence in 12 years) was associated with a lower risk of cancer death. Concretely, 10 points increase in the adherence was associated with a 7% (95% CI: 2–11%) decrease of cancer mortality risk. No consistent associations were observed between the other provegetarian diet scores (healthy and unhealthy score) and overall cancer mortality in this study, which was an unexpected finding since decreases in consumption of healthy plant foods were associated with a higher risk of all-cause mortality. Neither were there statistically significant associations when assessing the association between 12-year change in adherence to these scores with cause-specific cancer mortality (lung, breast, and colon), except for prostate cancer (HR per 10 points increase in adherence = 0.73; 95% CI: 0.55–0.96). Adjustment variables included many potential confounders related with medical conditions, as well as body mass index (BMI).

It was not possible to meta-analyze the results of both studies due to differences in the assessment of the adherence to the plant-based score, either at baseline [ 52 ] or over time [ 53 ]. The comparison groups differed in both studies too, with regard to high vs. low adherence to the provegetarian diet score [ 52 ], and change in adherence to the score vs. stable adherence over time [ 53 ]. None of the studies accounted for cancer treatment or other prognostic factors.

3.3. Mediterranean Diet

Our literature search retrieved 13 studies on the association between the MD (either the original MD scores (MDS), or its derivatives including the alternate MD (aMED), the modified MD (mMSD), the MD pattern (MDP), or the relative Mediterranean diet (rMED) scores) and cancer mortality and other related-outcomes [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Thus, the association between adherence to the MD and cancer mortality has been examined through five different a priori derived MD indexes. All studies were cohort studies, considering validated dietary assessment tools to evaluate the adherence to the MD, and all based the outcome assessment on reliable information sources (e.g., mortality and cancer registries). All studies controlled for relevant confounders (age, sex, region, energy intake, physical activity, education, and BMI), and several also considered comorbid conditions at baseline for adjustment [ 40 , 50 ]. Interestingly, none of the studies on the association between MD diet and overall cancer mortality risk controlled for prognostic-related factors in the analyses. More detailed characteristics of these studies are shown in Table 3 .

Characteristics of the studies evaluating the Mediterranean diet (high vs. low adherence) and cancer mortality including cause-specific cancer mortality.

HR = hazard ratio; SD = standard deviation; F = females; M = males; FFQ = food frequency questionnaire; 24-HR = 24 h recall; CRC = colorectal cancer; NA = not available; n = number of events; N = total population. Adjustments: 1: age; 2: smoking; 3: physical activity; 4: BMI; 5: education; 6: dietary score at baseline; 7: ethnicity; 8: total energy intake; 9: radiation treatment; 10: pack-years; 11: chemotherapy; 12: nonsteroidal anti-inflammatory drug (NSAID) use; 13: family history of colorectal cancer; 14: comorbidities; 15: marital status; 16: alcohol intake, 17: type 2 diabetes; 18: postmenopausal hormone replacement therapy; 19: race, 20: sex; 21: baseline examination year; 22: abnormal electrocardiogram; 23: dietary supplement use; 24: oral contraceptive use; 25: stage; 26: time since diagnosis; 27: age at first birth and parity; 28: menopausal status; 29: eeight change; 30: categories of treatment; 31: time between diagnosis and completion of the questionnaire; 32: socioeconomic status; 33: self-reported prevalent chronic diseases at baseline; 34: moderate to vigorous physical activity; 35: diet score; 36: family history of cancer in a first-degree relative; 37: sleep duration; 38: history of hypertension; 39: living alone; 40: Charlson comorbidity index; 41: aspirin use, 42: changes in smoking status; 43: family history of myocardial infarction; 44: family history of diabetes; 45: changes of physical activity; 46: changes in total energy intake; 47: weight change; 48: survey wave; 49: region; 50: nationality; 53: waist circumference; 54: potato intake; 55: egg intake, 56: polyunsaturated lipid intake; 57: sweet intake; 58: non-alcoholic beverage intake.

Among the studies analyzing the association between MDS adherence and cancer mortality risk [ 39 , 41 , 43 , 46 , 48 ], two studies showed a statistically significant protective association [ 39 , 41 ], but three studies did not support an association [ 43 , 46 , 59 ]. In this regard, Lassale et al. [ 39 ] studied this association in the European Prospective Investigation into Cancer and Nutrition (EPIC) study among 451,256 healthy participants, followed-up for 12.8 years. This study also evaluated adherence to rMED, and both MDS and rMED (high vs. low adherence) were associated with a statistically significant reduced overall cancer mortality risk (HR = 0.90; 95% CI: 0.88–0.92 and HR = 0.88; 95% CI: 0.86–0.90, respectively). The study by Vormund et al. [ 41 ], which included 17,861 Swiss men and women, also reported that a higher adherence to the MDS (vs. low) was associated with lower cancer mortality risk in both men and women (HR = 0.95; 95% CI: 0.92–0.99), although this association was stronger in men (HR = 0.92; 95% CI: 0.88–0.97) and absent in women. Furthermore, Lagiou et al. [ 43 ], in a cohort of 42,237 Swiss women, showed that a one-point increase in the MDS was not significantly associated with cancer mortality risk. On the other hand, a Spanish study conducted among 12,449 men and women [ 46 ], found that MDS was not significantly associated with cancer mortality risk. As for the MDP score, Cheng et al. [ 48 ] studied its association with cancer mortality risk within the prospective Iowa Women’s Health Study from the USA, which included 35,221 cancer-free women at baseline, of which 4665 died due to cancer during follow-up. The adjusted HR and 95% CI for all-cancer mortality among participants in the highest relative to the lowest quintile was 0.93 (95% CI: 0.84–1.03).

The characteristics of other MD indexes, such as the aMED [ 40 , 44 , 45 , 47 , 49 , 51 ], the mMED [ 50 ], and the rMED [ 39 , 42 ], are described in the original studies [ 30 , 63 ] and elsewhere [ 64 ]. In relation to their association with cancer mortality and other outcomes, the following results were reported: In general, the nine aMED studies suggested that high vs. low adherence to the aMED score was associated with a decreased cancer mortality risk [ 40 , 44 , 45 , 47 , 49 , 51 ]. It should be noted that HR and the corresponding 95% CIs were extracted from the figures in the study by Liese et al. [ 45 ]. This study analyzed the association within three cohorts in a standardized manner. Overall, the study showed the protective effects of the MD against cancer mortality. Two studies assessing the association with regard to the mMED score were included [ 50 ]. A study by Warensjö et al. [ 50 ] of 38,428 Swedish women, found that mMED was associated with a lower cancer mortality risk (HR high vs. low adherence = 0.81 95% CI: 0.69–0.94). Finally, the two rMED studies [ 39 , 42 ] showed diverging results: Lassale et al. [ 39 ] showed a statistically significant inverse association with cancer mortality risk (HR = 0.88; 95% CI: 0.86–0.90) when considering the entire EPIC study cohort, whereas Buckland et al. [ 42 ] concluded that a high compared with a low rMED score adherence was not associated with a significant reduction in mortality from overall cancer in the Spanish EPIC cohort (HR = 0.92; 95% CI: 0.75–1.12).

Pooled estimates of the effect size and 95% CIs for cancer mortality risk comparing high vs. low adherers to the MD (preferably for MDS and aMED) are depicted in Figure 2 and described below. Distinctions by type of MD score were not made. Only overall mortality could be assessed due to lack of studies on MD adherence and cancer-specific mortality (except one study on colorectal cancer mortality). There was no evidence for publication bias according to the funnel plot and Egger test (data not shown).

Meta-analysis under random-effects model (REM) with regard to adherers to the Mediterranean diet (MD) (high vs. low) and overall cancer mortality. F = females, M = males.

3.3.1. Overall Cancer Mortality

We included eight studies comparing extreme groups (high vs. low) of adherence to the MD [ 39 , 45 , 47 , 48 , 49 , 50 , 51 ]. There were two studies that did not report HR by these groups [ 41 , 43 ]. Moreover, the study by Buckland et al. [ 42 ] was also not considered for this meta-analysis due to population overlap with the study of Lassale et al. [ 39 ]. In addition, the study by Liese contributed only with women from the Women Health Initiative Observational Study (WHI-OS) [ 45 ]. The pooled analyses (combining 74,267 cancer deaths among 1,949,146 persons) revealed that overall cancer mortality risk was significantly reduced by 16% (95% CI: 11–30). However, there was significant heterogeneity between the studies (I2 = 84%, p < 0.001), which disappeared after excluding the study by Cuenca-Garcia et al. [ 46 ], while risk estimates remained the same.

3.3.2. Colorectal Cancer Mortality

The association between MD adherence and colorectal cancer mortality was assessed in one study [ 40 ]. In this study, conducted within the Multiethnic Cohort Study (MEC) with 4204 colorectal cancer events over follow-up and subsequent 1976 deaths (1095 were colorectal cancer-specific), a nonsignificant association was observed between high vs. low adherence to aMED and colorectal cancer mortality (HR = 0.90; 95% CI: 0.57–1.43). It is important to note that this was the only study controlling for cancer treatment variables in the analyses.

3.4. Post-Diagnosis Studies on Plant-Based Dietary Patterns and Cancer Outcomes

We identified six studies on this topic based on our literature search [ 54 , 55 , 56 , 57 , 58 , 59 ], complemented with studies included in previous reviews [ 11 , 12 ]. These studies were mostly focused on the MD as the reference dietary pattern, or other predefined PBDPs. Included outcomes were both cancer mortality and recurrence. A summary of the studies on post-diagnosis PBDPs and cancer mortality is shown in Table 4 .

Characteristics of the studies evaluating plant-based dietary patterns at post-diagnosis and cancer mortality and recurrence.

F = females; M = males; FFQ = food frequency questionnaire; 24-HR = 24 h recall; CRC = colorectal cancer; NA = not available. Adjustments: 1: antiestrogen use; 2: oophorectomy status; 3: tumor stage; 4: tumor site; 5: marital status; 6: age; 7: energy intake; 8: chemotherapy; 9: treatment; 10: smoking; 11: alcohol consumption; 12: multivitamin use; 13: physical activity; 14: menopausal status; 15: parity; 16: oral contraceptive use; 17: BMI; 18: weight change since diagnosis; 19: grade of tumor; 20: time since diagnosis; 21: chemotherapy; 22: year of diagnosis; 23: sex; 24 survival time from cancer diagnosis; 25: metastases; 26: occurrence of other cancers, 27: race; 28: socioeconomic status; 29: medical conditions; 30: hormone replacement therapy; 31: Gleason score; 32: pre-diagnostic Mediterranean diet.

Of the selected studies, there was only one intervention study [ 57 ]. This study was conducted within the Women’s Healthy Eating and Living (WHEL) Study, and included 3088 females with non-metastatic breast cancer, who were randomized into an intervention and control group. The intervention group received advice through telephone and cooking classes on how to adopt the plant-based diet defined as a low-fat and high-fiber diet, characterized by a daily intake of five vegetable servings, two glasses of vegetable juice, three fruit servings, 30 g of fiber, and 15% to 20% of energy intake from fat. The control group received advice on maintaining a healthy diet only. Compliance with the intervention was controlled through dietary records during the intervention phase, which lasted six months. Consideration was given to potential confounding of the association by prognostic factors of the disease, such as stage, and dietary habits at baseline. Results of this study did not support that a plant-based diet is associated with a reduced risk of cancer death or cancer recurrence. Although this was the only study available, the long follow-up, large sample size, low residual confounding risk, and the adequacy of procedures during the intervention and follow-up, makes the obtained results highly robust.

The remaining studies were cohort studies. Two of them were conducted within the NHS [ 54 , 55 ]. Both assessed the association between adherence to the MD by means of the alternate MD score (aMED) and cancer mortality with regard to breast cancer [ 55 ] or colorectal cancer [ 54 ]. Early-stage breast ( N = 2729) and colorectal cancer ( N = 1201) patients in these studies were females, who were diagnosed with the disease during the follow-up of the cohort and were followed-up thereafter for all-cause mortality and cancer cause-specific mortality. The cancer diagnosis and outcome was verified by reviewing clinical records and death certificates. Adherence to aMED was assessed by the use of the dietary information collected in two-yearly intervals with a FFQ. The aMED score, adapted from the traditional MD Trichopolou score, awards one point for intakes higher than the population median of vegetables, legumes, fruits, nuts, whole grains, fish, and monounsaturated:saturated fat ratio, and intakes less than the median in meat, and in alcohol if intake is outside a given range [ 64 ]. No statistically significant associations were found between high adherence to aMED (vs. low adherence) and breast or colorectal cancer mortality in this study, nor did the authors observe any association with regard to all-cause mortality in the breast or colorectal cancer survivors. All estimates were adjusted for relevant prognostic factors of the disease (e.g., tumor stage, cancer site, and treatment), as well as for the patient´s lifestyle or dietary habits before the cancer diagnosis. Another American cohort study, conducted within the HPFS, addressed the association between aMED and cancer mortality, particularly concerning prostate cancer mortality [ 58 ]. In this study, 4538 early-stage prostate cancer patients were followed-up since the cancer diagnosis until mortality or end of follow-up. Comparable methods were applied to collect dietary information and to ascertain cancer diagnosis and death. Likewise, by adjusting for prognostic factors of the disease and lifestyle/dietary habits before the diagnosis, a significant inverse association was observed between high vs. low adherence to the MD (both as aMED and MDS) and mortality from any cause (HR = 0.78; 95% CI: 0.67–0.90). However, statistical significance was not reached for mortality from prostate cancer.

Other post-diagnosis dietary indices that have been examined in relation to MD were the modified Mediterranean diet score (mMDS) and the traditional Mediterranean diet score (MDS), which are similar in their composition with respect to aMED [ 64 ]. The German PopGen Biobank Study [ 56 ], which included 1404 colorectal cancer patients (histologically confirmed), among which 204 died during six years of follow-up, reported that high vs. low adherence to the mMDS was associated with a reduced all-cause mortality risk among those patients. The study accounted for the influence of all possible prognostic factors and of pre-diagnostic adherence to the MD. Adherence to the MD by the mMDS at pre- and post-diagnosis was assessed using dietary information collected via FFQs administered in both time intervals. Lastly, within the National Health and Nutrition Examination Survey (NHANES) study [ 59 ], 240 participants who self-reported a cancer diagnosis of breast or gynecological cancers were followed-up during 10 years on average. Cancer mortality was assessed by death certificates from clinical records and mortality registers. Dietary information collected with a single 24 hour recall (HR) was used to score the participants into levels of adherence to the MDS. This study showed that high vs. low adherence to this score was not significantly associated with neither all-cause mortality nor breast cancer mortality.

It is worth noting that four of these studies also accounted for pre-diagnosis dietary information on PBDPs [ 55 , 58 , 59 , 63 ], which was considered for the adjustment of baseline dietary intake in some of these studies [ 58 , 63 ]. Only the study by Kim et al. [ 55 ] examined the effect of pre-diagnosis PBDPs (aMED score) on cancer mortality among cancer survivors. As a result, no association was reported for total mortality, breast cancer mortality, distant recurrences or non-breast cancer mortality.

Results of the meta-analyses of these studies by cancer site were only possible for breast and colorectal cancer. No study evaluated the association between post-diagnosis PBDPs and cancer mortality in relation to all-cause mortality. Publication bias was unlikely according to funnel plots and Egger test.

3.4.1. Breast Cancer Mortality

Of the three studies evaluating an association between a PBDP and cancer mortality, there were two cohort studies considering an MD score and breast cancer mortality [ 55 , 59 ]. The intervention study was not considered for the meta-analysis due to its different nature. Pooled estimates for the 2849 breast cancer patients revealed that adherence to the MD (high vs. low) was not associated with all-cause mortality among breast cancer survivors (RR = 0.87; 95% CI: 0.85–1.01). While heterogeneity between the studies was not apparent (I 2 = 0%, p = 1), the study by Karavisouglou contributed with a small number of breast cancer patients, whose diagnoses were not confirmed [ 59 ]. Moreover, in this study, breast and gynecological cancers were considered together, thus biasing the pooled analyses to some extent. The other two studies provided more robust results [ 55 , 57 ], and supported that a PBDP from breast cancer onset reduces all-cause or breast cancer mortality.

3.4.2. Colorectal Cancer Mortality

The studies by Fung [ 54 ] and Ratjen [ 56 ] were the only two studies available on the association between PBDP and cancer mortality in colorectal cancer survivors. The MD was considered as a plant-based pattern in both studies, either as aMED or mMDS. Together, these studies combined the results of 2605 colorectal cancer patients. The summary estimates for all-cause mortality revealed a nonsignificant association (HR = 0.66; 95% CI: 0.37–1.17); no other outcome events could be analyzed due to lack of data. However, there was heterogeneity between both studies (I 2 = 79%, p = 0.03), possibly driven by differences inherent to the study populations (country of recruitment, gender distribution, and clinical characteristics of the patients). It was not possible to examine the influence of these variables on the pooled results.

4. Discussion

The present review is the first to address the available evidence on the association between PBDPs and cancer-related outcomes, including overall cancer mortality, cause-specific mortality, and cancer recurrence. Plant-based diets have been traditionally regarded as vegetarian diets, but other definitions of plant-based foods can be considered by rating negatively some or all animal foods, and even accounting for the quality of plant-based foods in the diet. Only adherence of the MD was found to reduce overall cancer mortality risk, but none of the studies accounted for the influence of prognostic factors on this association; thus, the true independent effect of the MD with cancer mortality risk remains inconclusive. Studies on other PBDPs in relation to these cancer outcomes have provided nonsignificant or ambiguous results. The same was found for post-diagnostic studies on these associations. Therefore, for the considered cancer-related outcomes, there is still insufficient evidence for asserting that PBDPs help in reducing the risk of these outcomes.

Plant-based diets are dietary sources of several bioactive compounds such as fiber, phenol, polyphenol, and sulfur compounds, and other antioxidants compounds including vitamins [ 7 ]. In the literature, foods of vegetable origin have been associated with cancer mortality outcomes, although conflicting results have been reported. These include, for example, legumes [ 9 ], fruits and vegetables [ 15 ], nuts [ 16 ], whole grains [ 16 ], and olive oil [ 18 ]. Bioactive compounds in these foods, however, have been shown to have anti-carcinogenic effects in experimental models and epidemiological studies [ 7 ]. For instance, high intake of fiber and polyphenols from cereals have been shown to reduce cancer mortality risk [ 65 , 66 , 67 ]. As for cancer incidence, a two-tier mechanism could explain how these compounds could prevent cancer mortality risk: first, fiber, mostly soluble fiber, modulates the gut microbiota composition improving the colonic barrier functions, and second, substrates such as resistant starch, non-starch polysaccharides (β-glucans), and phenols are metabolized into active metabolites by the commensal microbiota [ 68 ]. The resulting metabolites have well known anti-cancer effects and could likewise prevent cancer mortality. For instance, phenolic acids are antioxidants with free-radical scavenging activity. Free radicals play an important role not only for cancer development but also in cancer treatment since anti-cancer drugs generate reactive oxygen species themselves [ 69 ]. Therefore, neutralizing their damaging effects is crucial to reduce mortality and secondary outcomes in cancer patients. Other metabolites, such as short-chain fatty acids are also major players in the maintenance of gut integrity and immune homeostasis, to prevent tumor development [ 68 ].

The drawbacks of individual nutrient or foods studies have been repeatedly described [ 19 ]. PBDPs or indexes based on the potential beneficial effects of various dietary factors, and accounting for the interaction of all phytochemicals contained in the diet, should be therefore a better approach to examine the association between plant-based diets and cancer mortality. PBDPs have been related to a low-risk immunological profile (lower C-reactive protein, fibrinogen, and leukocyte levels) [ 70 ], lower adiposity markers [ 62 ], and better antioxidant status [ 71 ]. These are probably the underlying mechanisms by which these diets could improve the immune response in cancer patients, while also slowing tumor growth and risk of developing subsequent events.

Vegetarian diets are based on the consumption of plant-based foods, namely vegetables, fruits, whole grains, legumes, nuts, and seeds, with the elimination of foods of animal origin such as meat, poultry, wild game, seafood, and their byproducts [ 72 ]. In a narrower sense, vegetarian diets may or may not include eggs and dairy products. Vegan diets, for instance, exclude these dietary factors, whereas lacto-, ovo-, and lacto-ovo vegetarians include either dairy products, or eggs and egg products, or both dairy products and eggs, respectively. Vegetarian diets comply with healthy diet recommendations and are therefore considered a healthful dietary pattern [ 72 ]. A negative side of this dietary pattern is the potential deficient intake of certain nutrients such as iron and vitamin B12. Long-chain n-3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are lower in vegetarians and typically absent in vegans [ 73 ]. Decreased intakes of some of these nutrients have been related to a higher cancer incidence in some studies [ 74 ]. On the contrary, the reduced intake of heme-iron in vegetarians is presumed to be beneficial taking into consideration that high ferritin levels due to iron overload have been related to a higher risk of certain cancers [ 75 ]. However, it is considered that if vegetarian diets are well-planned, their naturally high content of beneficial bioactive compounds outweigh the negative sides [ 72 , 76 ]. Indeed, it has been reported that vegetarians have a lower cancer incidence than nonvegetarians [ 26 ], or at least regarding colorectal cancer for semi-vegetarians or pesco-vegetarians compared to nonvegetarians [ 77 ]. While the results of our review tended to suggest that vegetarians and vegans have a lower risk of cancer mortality and cancer-specific mortality when compared to nonvegetarians, we did not observe significant associations in meta-analyses combining results of the selected studies. By updating a previous review examining vegetarian diets regarding several health issues [ 26 ], we provide more consistent data, although it is still insufficient to provide meaningful conclusions. Indeed, vegetarians do not make up large population groups and are therefore difficult to ascertain in epidemiological studies. Moreover, as shown in the study by Key et al. [ 60 ], vegetarians or vegans often adopt a healthier lifestyle (e.g., non-smoking) as compared to omnivores, making it more difficult to establish comparisons between both groups. The sample size of the included studies was too limited to permit overall and cause-specific cancer mortality studies. Another important aspect as to why we probably did not observe a significant overall effect might be due to different considerations of vegetarians, vegans, and type of vegetarian diets among the studies. Based on the responses to a finite list of foods, participants were classified into vegetarians and vegans in most studies; only the study by Orlich based this classification upon a validated FFQ [ 61 ]. Misclassification of vegetarian diets was therefore likely in these studies. In addition, it was not possible to make any comparisons with regard to type of vegetarian diet since few studies attempted to link the type of diet with cancer mortality risk [ 38 ]. Thus, for example, whether pesco-vegetarian or lacto-vegetarian diets, rich in dietary factors with colorectal cancer prevention potential (e.g., calcium, fiber, n-3 fatty acids, and vitamin antioxidants), have a stronger prevention effect against mortality of this disease could not be confirmed.

Recently, a priori-defined plant-based scores have been proposed to allow comparisons between different levels of compliance with vegetable-derived foods against animal-derived foods [ 53 ]. Provegetarian food pattern scores are newly developed tools to assess the level of adherence to a vegetarian-like diet (i.e., preference of plant-based foods). Unlike the vegetarian dietary patterns, these scores consider moderate intakes of animal foods such as fish, poultry, and dairy in the assessment of the score, under the assumption that moderate intake of these foods may confer some health benefits [ 78 , 79 , 80 ]. Moreover, in this manner, these scores are presumed to overcome the potential nutrient intake deficiencies (e.g., vitamin B12), that a strict plant-based diet such as the vegetarian diet poses. Accordingly, they score vegetable-derived foods positively, while all animal-derived foods are scored negatively. However, with only two studies evaluating how these scores affect cancer mortality risk [ 52 , 53 ], it has been difficult to arrive at any concrete conclusion. The time point considered for the assessment of the provegetarian diet differed in both studies. Furthermore, both studies were not comparable in the sense that the provegetarian diet score was not defined in the same way. While both considered all animal foods, only the study by Baden et al. [ 53 ] distinguished the quality of plant-based foods in the scoring. This study reported associations for a standard provegetarian diet score, and for its healthy and unhealthy versions. Relative to the unhealthy score, the healthy one scored more negatively foods rich in refined carbohydrates, which are supposed to be implicated in cancer risk through energy metabolism, insulin, and insulin-like growth factor (IGF-1) upregulations. A major impact of the healthy provegetarian diet score for cancer mortality prevention was therefore expected. Nevertheless, significant associations were only observed for the standard score.

The MD encompasses the traditional dietary pattern found in the olive-growing regions of the Mediterranean basin in the 1960s [ 81 ], and is globally recognized as a healthy dietary model [ 82 ]. The traditional MD pattern is a well-defined plant-based dietary pattern characterized by: the daily use of olive oil; an abundance of plant foods such as fruits and vegetables, nuts and seeds, cereals and legumes; the consumption of fish and seafood especially in coastal regions; moderate-to-low intake of dairy products mostly from fresh cheese and yogurt; moderate alcohol mostly in the form of wine; and a less frequent consumption of meat and meat products [ 83 ]. Thus, the MD pattern is distinctively plant-based, and thus a valuable alternative to the vegetarian diet, as it provides a good supply of fiber, phytochemicals, vitamins, and minerals, even closing some nutritional gaps of the vegetarian diet [ 83 ]. For the reasons cited above, we considered the MD as a reference PBDP. Moreover, the MD is presumed to boost the endogenous antioxidant defense and the immune system to prevent cancer and, possibly, also fatal outcomes of this disease. With respect to cancer incidence, indeed, as is also the case with other dietary patterns, the MD is an established dietary pattern for cancer prevention [ 13 , 84 ]. Other dietary patterns resembling plant-based diets such as the very low ketogenic diet, seem to have cancer prevention potential through weight loss and related mechanisms, but have been scarcely examined with regard to cancer mortality [ 85 ].

Since the first definition of an MD index, multiple adaptations have been created to improve its conformity to the MD [ 64 ]. The MD scores used to assess the association between the MD and cancer mortality risk are the MDS, MDP, rMED, and aMED. Pooled analyses of the included studies revealed a significant inverse association between high vs. low adherence to the MD and overall cancer mortality risk. While we combined the studies regardless of the MD score, it has been reported that there is only moderate concordance between them [ 86 ]. Indeed, MD scores vary largely in the types of foods included and the intake levels in the population. Thus, variability in the scoring schemes of the MD scores might have affected our results. However, when restricting our meta-analysis to studies using the MDS (the predominant score), the result was maintained (data not shown). Despite the fact that our results support a beneficial effect of the MD for the prevention of cancer mortality, we have to be cautious in the interpretation of these results. No study considered the influence of relevant factors related with the disease outcomes, such as treatment, on the associations. In addition, there was scarce data on the association between MD and cancer mortality by type of cancer.

As outlined before, most of the studies on the association between PBDPs and cancer mortality considered the influence of such diets from pre-diagnosis states to the event outcomes. However, post-diagnosis diet might have a strong short-term or even long-term effect on cancer mortality and other related outcomes. Whether eating a PBDP after cancer diagnosis affects cancer outcomes has been addressed in several studies. Although these studies accounted for a large number of factors related to the outcome (all potential prognostic factors: clinical and pathological tumor characteristics, treatment, and comorbidities), their results must be interpreted with caution due to the limited sample sizes. Moreover, there was only one intervention study on the effect of a well-defined plant-based diet on cancer-related outcomes [ 57 ]. Importantly, this study did not address whether consuming the high vegetable/fruit/fiber and low-fat diet of the study intervention early in life would alter the risk of breast cancer and cancer mortality as well. The remaining studies were cohort studies assessing the association between adherence to the MD since the cancer diagnosis and cancer mortality [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 58 , 59 ]. Some [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ], but not all [ 54 , 55 , 56 , 57 , 58 , 59 ], of the included studies also accounted for dietary behaviors before the cancer onset. In fact, as this review shows, dietary patterns over a lifetime are likely to influence cancer mortality. Future studies on the association between PBDPs and cancer mortality should therefore consider assessing adherence to PBDPs throughout the lifespan, to cover pre- and post-diagnostic influences of these dietary patterns on the associations.

Thus, while dietary patterns have been consistently associated with a reduction of cancer incidence, an association with cancer mortality has not been clearly established. This contradiction could be explained by the fact that cancer mortality is greatly influenced by the type and treatment regime. Indeed, cohort studies assessing the association from a pre-diagnosis state typically did not account for this factor. Rather, this was accounted for in studies evaluating how adherence to these plant-based diets since diagnosis impacts on these outcomes. On the other hand, the lack of statistical power to detect significant associations in cause-specific mortality studies is another important limiting factor that makes it impossible to draw any meaningful conclusions on this association. In fact, there are no studies on cause-specific cancer mortality other than lung cancer, breast cancer, colon cancer, and prostate cancer. Also of note, is the fact that studies on other cancer-related outcomes, such as secondary cancers, are unavailable. No study considered the interaction between dietary and genetic factors on these associations. Most studies relied on a single measurement of diet at baseline, but dietary patterns may change over time and the length of exposure to plant-based-like dietary patterns may account for the differences observed between results from different cohorts. Dietary assessment tools (3-day records, 24-h recalls or FFQs) also differed greatly between the studies, as well as the studied populations. For instance, there were both pre and postmenopausal breast cancer patients considered jointly in some studies. Moreover, while the definitions of vegetarians and vegans were well-defined, some studies seemed to mix up vegans and vegetarians. Further, in the case of the comparison groups, there were differences among the studies with regard to the definition of meat eaters (omnivores). The included studies considered either populations of adherers to a specific PBDP (for example, vegans and vegetarians) or cohorts with individuals classified into different levels of adherence to PBDPs (for example, MD adherence groups) according to their reported dietary data. Therefore, the possibility that some studies misclassified vegetarians, vegans or adherence to other types of plant-based diets cannot be ruled out. Finally, plant-based diets contain a huge variability of bioactive compounds depending on the dietary source, which makes the definition of a healthy plant-based diet particularly complex. Among the limitations of this review, there were also issues related to population overlap in the vegetarian studies [ 35 , 38 ], which could have introduced bias to our results. We could also not analyze whether duration of adherence to any PBDP had any influence on the results.

There are also strengths of this review worthy of consideration: this is the first review and meta-analysis that has analyzed all the available data on PBDPs in relation to cancer mortality and related outcomes. While a rapid review was conducted, we complemented the identification of studies with those included in other reviews related to our topic. However, a quality assessment of these studies was not performed. We were able to conduct analyses by some cancer types and to evaluate the influence of some study characteristics on the results. However, we were not able to meta-analyze studies according to all cancer types due to lack of studies.

5. Conclusions

This review and meta-analysis of the current available evidence on the association between PBDPs and cancer mortality show that there is limited evidence regarding the beneficial effects of vegetarian diets for the prevention of cancer-related outcomes in the general population and in cancer survivors. This review also shows that there is suggestive evidence regarding the association between the MD pattern and cancer mortality. There were very few studies evaluating how these dietary patterns influence cancer mortality after the cancer diagnosis. Breast cancer and colorectal cancer outcomes were by far the most studied cancer types, but the number of studies is small. Thus, there is an urgent need to increase our knowledge on the usefulness of plant-based diets for the prevention of cancer mortality. Well-designed studies, considering consensus definitions of PBDPs and all pertinent factors including prognostic factors of the disease, genomics, and others, are needed to determine the effect of plant-based diets on cancer survival and cancer recurrence, before and after the diagnosis of cancer.

Acknowledgments

The authors would like to acknowledge Dafina Petrova for her contributions in editing and proofreading the manuscript.

Search strategy applied to retrieve the studies (date: 20 April 2020)

#1) “Survival” OR “Progression-Free Survival” OR “Disease-Free Survival”

1217,476 results

#2) “Mortality”

1125,551 results

#3) “Cancer Survivors”

16.142 results

#4) #1 OR #2 OR #3

1984,149 results

#5) (“Diet, Vegetarian” OR “Diet, Paleolithic” OR “Diet, Ketogenic” OR “Diet, Healthy” OR “Diet, Mediterranean” OR “Diet, Protein-Restricted” OR “Diet, Macrobiotic” OR “Diet, Carbohydrate Loading” OR “Diet, Vegan” OR “Caloric Restriction” OR “Dietary Approaches To Stop Hypertension”)

23,070 results

#6) #4 AND #5

2234 results

B. Flow diagram illustrating the process of article selection.

Author Contributions

Conceptualization, E.M.-M., E.S.-F., B.G.-V., and M.J.S.; methodology, E.M.-M.; formal analysis, E.M.-M., E.S.-F., and B.G.-V.; data curation, E.S.-F.; writing—original draft preparation, E.M.-M. and E.S.-F.; writing—review and editing, E.M.-M., E.S.-F., B.G.-V., and M.J.S.; supervision, M.J.S. All authors have read and agreed to the published version of the manuscript.

This research was funded by CIBER Epidemiología y Salud Pública CIBERESP.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.