There are several types of plant-based diets, with unknown differences across diets on total/plant protein intake and variety of plant protein sources consumed.
This systematic review compares total protein intake, proportion of plant proteins and main plant-protein sources consumed across four primarily plant-based diets: vegan, vegetarian, pesco-vegetarian and semi-vegetarian.
We included observational studies reporting on protein intake and/or protein sources in generally healthy adults that were published between 2002 and 2023. We determined (i) % energy from total and plant protein, (ii) the proportion of plant protein relative to total protein intake and (iii) main plant protein sources (median % contribution of each source to total plant protein intake; interquartile range) consumed across the four diets. The plant protein sources were broadly classified into United States Department of Agriculture (USDA) food-groups: "grains", "nuts and seeds", "soy-products" and "beans, peas, lentils".
We included 13 studies reporting on protein intake/sources that were conducted in the US, Europe, and South Korea. Of these, 7 reported on vegan, 11 on vegetarian, 7 on pesco-vegetarian and 7 on semi-vegetarian diets with total protein intake ranging from 10-17.4%. Vegan diets had the highest plant protein proportion (ranging from 77-98%) and semi-vegetarian diets the lowest (ranging from 37-83%). Plant protein source contribution was highest from grains (ranging from 60-78%). Nuts and seeds were most consumed in vegetarian diets (7.9%;2.9-10.3%) and least in semi-vegetarian diets (3.7%;2-14.8%). Soy products, beans, peas, and lentils were most consumed in vegan diets (17.3%;16.3-19.9 and 19.6%;14.6-21.3, respectively) and least in semi-vegetarian (3.7%;1.3-13.9 and 8.5%;5.2-10.2) diets.
Vegan diets had the highest plant protein proportion and a variety of plant protein sources, while semi-vegetarian diets had the lowest plant protein proportion and mainly relied on grains as a plant protein source.