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Diet consisting mostly or entirely of plant based foods

A plant based diet is a diet consisting mostly or entirely of plant based foods. Plant based diets encompass a wide range of dietary patterns that contain low amounts of animal products and high amounts of fiber rich plant products such as vegetables, fruits, whole grains, legumes, nuts and seeds. They do not need to be vegan or vegetarian, but are defined in terms of low frequency of animal food consumption. Campbell's research about a plant based diet extended from The China Project, a decade long study of dietary practices in rural China, giving evidence that a diet low in animal protein and fat, and high in plant foods, could reduce the incidence of several diseases. In 2005, Campbell and his son published The China Study, a best selling book emphasizing the potential health benefits of a plant based diet. Campbell also used the plant based concept to educate consumers about how eating meat had significant environmental consequences. A plant based diet may be defined as consuming plant sourced foods that are minimally processed. In 2021, the World Health Organization (WHO) stated that "plant based diets constitute a diverse range of dietary patterns that emphasize foods derived from plant sources coupled with lower consumption or exclusion of animal products. Vegetarian diets form a subset of plant based diets, which may exclude the consumption of some or all forms of animal foods." The WHO lists flexitarian, lacto vegetarian, lacto ovo vegetarian, ovo vegetarian, pescatarian and vegan diets as plant based. Main motivations to follow a plant based diet appear to be health aspirations, taste, animal welfare, environmental concern, and weight loss. In the U. S. A., people take individual action on climate change through their diet. Twenty six per cent of those who eat a plant based diet because they are "alarmed" about global warming — defined by the Yale Program on Climate Change Communication as those who are "convinced global warming is happening, human caused, an urgent threat" — and twenty seven per cent eat a plant based diet because they are "concerned" — they believe global warming is a real and serious threat and that humans are causing it, but they think climate impacts remain far enough in the future that they are a lower priority issue.

Plant based diets are of interest in preventing and managing chronic diseases. The British Dietetic Association have stated that a plant based diet "can support healthy living at every age and life stage", but as with any diet it should be properly planned. With processed plant based foods, such as vegan burger patties or chicken like nuggets, becoming more available, there is also concern that plant based diets incorporating these foods may become less healthy. In practice lacto ovo vegetarians or vegans seem to have a higher overall diet quality compared with nonvegetarians. The reason for this is the closer adherence to health organisation recommendations on consumption of fruits, whole grains, seafood and plant protein and sodium. The higher diet quality in vegetarians and vegans may explain some of the positive health outcomes compared with nonvegetarians.

Plant based foods are not a reliable source of Vitamin B12 by default. A lack of B12 is associated with a range of conditions and it is essential for human health. Those eating a fully plant based diet should ensure adequate B12 intake via supplementation or consumption of fortified foods, such as fortified plant milks or yogurts, nutritional yeast, or fortified cereals. Even those eating a plant based diet including a small amount of animal products are at an increased risk of a lower than recommended B12 intake without supplementation or regular consumption of fortified foods.

Observational studies show that vegetarian diets are lower in energy intake than non vegetarian diets and that, on average, vegetarians have a lower body mass index than non vegetarians. Two reviews of preliminary research found that vegetarian diets practiced over 18 weeks or longer reduced body weight in the range of , with vegan diets used for 12 weeks or longer reducing body weight by 4 kg. In obese people, a 2022 review found that plant based diets improved weight control, LDL and total cholesterol, blood pressure, insulin resistance, and fasting glucose.

Some reviews indicate that plant based diets including fruits, vegetables, whole grains, legumes, and nuts are associated with a lower risk of diabetes. Therefore, vegetarian and vegan diets are under clinical research to identify potential effects on type 2 diabetes, with preliminary results showing improvements in body weight and biomarkers of metabolic syndrome. When the focus was whole foods, an improvement of diabetes biomarkers occurred, including reduced obesity. In diabetic people, plant based diets were also associated with improved emotional and physical well being, relief of depression, higher quality of life, and better general health.

Plant based diets are associated with a decreased risk of colorectal and prostate cancer. Vegetarian diets are associated with a lower incidence from total cancer ( 8%). A vegan diet seems to reduced risk of incidence from total cancer by 15%. However, there was no improvement in cancer mortality.

Preliminary studies indicate that a plant based diet may improve the gut microbiome.

A 2022 review of prospective cohort studies showed that vegetarian diets are associated with a 15% reduced risk of cardiovascular diseases and 21% reduced risk in coronary artery disease, but with no effect on the risk of stroke; for vegan diets, only a reduced risk in coronary artery disease was found. Other reviews found that plant based diets, including vegan and vegetarian diets, may lower the risk of cardiovascular diseases, and blood lipid levels. Randomized clinical trials also showed that the reduction in blood pressure (about 4 mmHg) associated with a vegan diet without caloric restrictions is comparable to reductions observed with dietary practices recommended by medical societies and use of portion controlled diets. Preliminary evidence indicates that people on a long term vegan diet show improvements in cardiovascular and metabolic risk factors.

The effect of plant based diets on bone health is inconclusive. Preliminary research indicates that consuming a plant based diet may be associated with lower bone density, a risk factor for fractures.

Plant based diets are under study for their potential to reduce inflammation. C reactive protein a biomarker for inflammation may be reduced by consuming a plant based diet, particularly in obese people.

A 2020 review stated that dietary patterns based on consuming vegetables, fruits, legumes, nuts, whole grains, unsaturated vegetable oils, fish, lean meat or poultry, and are low in processed meat, high fat dairy and refined carbohydrates or sweets, are associated with a decreased risk of all cause mortality.

In a meta analysis published online in 2023, plant based diets were shown to have a moderate positive effect on aerobic performance and had no effect on strength performance.

A reduction in meat consumption and a shift to more plant based diets is needed to reach climate targets, addressing public health problems, and protecting animal welfare. Research has been done on how to best promote such a change in consumer behaviour. Some public health organisations advocate a plant based diet due to its low ecological footprint. These include the Swedish Food Agency in its dietary guideline and a group of Lancet researchers who propose a planetary health diet. Vegan climate activist Greta Thunberg also called for more plant based food production and consumption worldwide. A 2022 report by the Stockholm Environment Institute and the Council On Energy, Environment and Water included protecting animal welfare and adopting plant based diets on a list of recommendations to help mitigate the ecological and social crises bringing the world to a "boiling point". Denmark and South Korea announced plant based action plans in 2023.