Plant-based diet

thumb|Plant-based dishes

A plant-based diet is a diet consisting mostly or entirely of plant-based foods. It encompasses 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, seeds, herbs and spices. Plant-based diets may also be vegan or vegetarian, but do not have to be, as they are defined in terms of high frequency of plants and 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's book 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.

Motivation and prevalence

As of the early 21st century, some 4 billion people are estimated to live primarily on a plant-based diet, some by choice and some because of limits caused by shortages of crops, fresh water, and energy resources. 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. Roughly a third of greenhouse gas emissions are linked to food production and transportation. The most greenhouse gas emissions from food come from agriculture and land use, and over 66% of agriculture land is used to grow food for livestock (a mere 8% is used to directly grow food that human will consume).

Health guidelines and research

thumb|Countries' positions on [[Vegetarianism|vegetarian diets within their food-based dietary guidelines:

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Plant-based diets are of interest in preventing and managing chronic diseases. The British Dietetic Association 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.

Diet quality

Not all plant-based foods are equally healthy. Rather, plant-based diets including whole grains as the main form of carbohydrate, unsaturated fats as the main form of dietary fat, an abundance of fruit and vegetables, and adequate n-3 fatty acids can be considered healthy.

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.

Vitamin B₁₂

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.

Weight

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.

Diabetes

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.

Cancer

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 reduce risk of incidence from total cancer by 15%. However, there was no improvement in cancer mortality.

Microbiome

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

Cardiovascular diseases

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.

Bone health

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.

Inflammation

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.

Mortality

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.

Physical performance

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.

Sustainability