Plant-Based Diet

The term and its proponents

A 2025 survey of dietitians in the United Kingdom and Ireland, published in the Journal of Human Nutrition and Dietetics, states that there is no consensus definition of a plant-based diet. The authors describe it as a dietary pattern centered on predominantly plant foods while minimizing or excluding animal-based foods, akin to vegetarian, vegan or flexitarian patterns.

The same paper says the related term whole food plant-based diet was first coined by T. Colin Campbell of Cornell University and later adopted by several public health agencies, including the World Health Organization. This is the authors' own attribution, cited to earlier work they reference, and the sources reviewed here do not trace the first use of the phrase independently or date it.

Gaps in the historical record reviewed

The sources reviewed for this page do not document the histories of specific clinical programs associated with plant-based eating, nor do they date the shift of the phrase from a descriptive label to a marketing term. The history of vegetarian and vegan eating, including religious and ethical traditions, is treated on the Vegetarian Diet and Vegan Diet pages. The wider family of eating patterns appears on the Dietary Approaches page.

An umbrella term with varying definitions

A review in the European Journal of Clinical Nutrition examined how researchers use the term plant-based diet in nutrition intervention studies. About half of the retrieved intervention studies completely excluded animal products and used the term interchangeably with a vegan diet. About a third of trials included dairy products, and about 20 percent of interventions emphasized a semi-vegetarian pattern.

The review concluded that the umbrella term can cause significant ambiguity, noted that descriptions of interventions were often incomplete, and urged authors to use the term only with a detailed dietary description. It also called for a consensus definition. Findings reported under the label plant-based diet therefore may not describe the same eating pattern from one study to the next.

Diet quality indices

Researchers at the Harvard T.H. Chan School of Public Health built three scores from food-frequency questionnaires: an overall plant-based diet index, a healthful index in which whole grains, fruits, vegetables, nuts, legumes, oils and tea or coffee scored positively, and an unhealthful index that scored refined grains, juices, sweetened beverages, potatoes and sweets positively. In all three, animal foods received reverse scores.

These indices measure how heavily a diet leans toward plant foods, and the healthful and unhealthful versions separate plant food quality from plant food quantity. They are research constructs and differ from a diet that a person or program labels plant-based. Related pages on Machipedia include Vegetarian Diet, Vegan Diet and Mediterranean Diet.

Patterns the label covers

Sources describe plant-based eating as a spectrum. At one end are vegan diets that exclude all animal products, and at the other are patterns that include meat, fish and dairy in varying amounts. A cohort of Adventist Health Study-2 participants was categorized into five patterns: nonvegetarian, semivegetarian, pescovegetarian, lacto-ovovegetarian and vegan.

Whole food plant-based diets, as the 2025 dietitian survey describes them, emphasize minimally processed foods such as fruits, vegetables, whole grains, legumes, nuts and seeds while limiting animal foods. The same paper notes that a plant-based label does not always take overall diet quality or nutritional adequacy into account.

Professional involvement

Dietitians are the professionals most often named in the sources for planning vegetarian and plant-based diets. The British Dietetic Association page on vegetarian, vegan and plant-based diets advises speaking to a dietitian before taking an iodine supplement. In the 2025 survey, 76 percent of 335 registered dietitians in the United Kingdom and Ireland agreed that a well-planned whole food plant-based diet is suitable for all stages of life. Machipedia covers the profession under Dietetics and a related complementary field under Nutritional Therapy.

Uses described by professional bodies and authors

The Academy of Nutrition and Dietetics position paper states that appropriately planned vegetarian, including vegan, diets may provide health benefits for the prevention and treatment of certain diseases. It names ischemic heart disease, type 2 diabetes, hypertension, certain cancers and obesity among the conditions for which vegetarians and vegans are at reduced risk.

Environmental claims

The same paper also states that plant-based diets are more environmentally sustainable than diets rich in animal products. Environmental claims lie outside the health evidence summarized on this page, and the other sources reviewed here do not evaluate them, so no environmental findings are reported beyond this statement of the position paper.

Cohort studies of diet indices

In three US cohorts totaling 69,949 women and 40,539 men without chronic disease at baseline, higher overall and healthful plant-based diet indices were associated with lower type 2 diabetes incidence. Hazard ratios for the extreme deciles were 0.51 for the overall index and 0.55 for the healthful index, over 4,102,369 person-years and 16,162 cases. These are observational data, and diet was self-reported.

In a related analysis of coronary heart disease with 8,631 cases, the healthful index was associated with lower incidence (hazard ratio 0.75 for extreme deciles) and the unhealthful index with higher incidence (1.32). The overall index showed a hazard ratio of 0.92 with a confidence interval of 0.83 to 1.01. A mortality analysis found that improving healthful index scores over 12 years was associated with lower total and cardiovascular mortality, while rising unhealthful scores were associated with higher mortality.

Vegetarian and vegan cohorts

The Adventist Health Study-2 included 88,400 participants and 12,515 deaths. Compared with nonvegetarians, vegetarians had lower risks of mortality overall at age 65 (hazard ratio 0.89), though the estimate at age 85 was close to 1 (0.98). Hazard ratios depended on age, and the study is observational.

An umbrella review of 21 systematic reviews, mostly of observational evidence, reported that vegetarian dietary patterns, including vegan, were associated with lower cardiovascular disease incidence (relative risk 0.85) and cardiovascular mortality (hazard ratio 0.92) than non-vegetarian diets. The reviewers also reported reductions in blood pressure, LDL cholesterol and body mass index for vegan patterns compared with non-vegetarian ones.

Randomized trials

A meta-analysis of 30 randomized trials in adults found that vegetarian or vegan diets, compared with omnivorous diets, reduced total cholesterol, LDL cholesterol and apolipoprotein B, with no significant difference in triglycerides. A systematic review of 7 randomized trials with 770 adults with type 2 diabetes reported a lower hemoglobin A1c and body mass index with vegetarian patterns, rated moderate certainty, and no effect on fasting glucose, fasting insulin or LDL cholesterol.

These trials tested vegetarian or vegan diets rather than the broader plant-based label, and follow-up was limited. The searches run for this page, in PubMed and Europe PMC, did not locate a Cochrane review specific to plant-based diets, and the sources reviewed do not report trials of hard cardiovascular outcomes for these diets.

Position statements

The Academy of Nutrition and Dietetics states that appropriately planned vegetarian and vegan diets are nutritionally adequate and appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood and for athletes. The British Dietetic Association page states that plant-based diets can support healthy living at every age and life stage if eating is planned to meet nutritional needs. Both statements depend on planning.

A narrative review of position papers on vegan diets for children found disagreement. Some associations support well-designed vegan diets with careful planning, vitamin B12 supplementation and supervised medical and dietetic oversight, while specific pediatric associations caution against vegan diets for children and adolescents, citing potential harm and a lack of adequate substantiation.

Nutrients of concern

The British Dietetic Association page states that the only reliable sources of vitamin B12 for vegans are fortified foods and supplements. It says plant iron is absorbed less efficiently than iron from meat and eggs. It says dairy and seafood are the main iodine sources, so exclusively plant-based eaters may be at risk of deficiency, and that too much iodine is also harmful.

For omega-3 fatty acids, the page says oily fish is the richest source, plant sources can be converted by the body, and algae-based supplements are suitable for vegans. It says calcium without dairy should come from fortified alternatives and foods such as calcium-set tofu, and links vitamin D to bone health. The Academy statement similarly says vegans need reliable sources of vitamin B-12. This page gives no amounts or dosing.

Eating disorders and care boundaries

A 2026 meta-analysis of 26 cross-sectional studies with 23,783 participants found that adults following vegetarian or vegan diets had moderately higher orthorexia nervosa symptoms than omnivores (standardized mean difference 0.46). The authors urged caution because heterogeneity was high and study quality low, and the cross-sectional design cannot show cause. This page does not otherwise establish a link between plant-based eating and eating disorders.

Anyone with a medical condition, pregnancy, an eating disorder or a child's diet to plan is directed by the sources to professional dietetic input. A diet should not delay or replace necessary medical care.