Protein Adequacy, Plant Protein Proportion, and Main Plant Protein Sources Consumed Across Vegan, Vegetarian, Pescovegetarian, and Semivegetarian Diets: A Systematic Review.

Background: 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.

Objectives: This systematic review aimed to compare total protein intake, proportion of plant proteins, and main plant protein sources consumed across 4 primarily plant-based diets: vegan, vegetarian, pescovegetarian, and semivegetarian.

Methods: 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 the following: 1) % energy from total and plant protein; 2) the proportion of plant protein relative to total protein intake; and 3) main plant protein sources (median percentage contribution of each source to total plant protein intake; interquartile range) consumed across the 4 diets. The plant protein sources were broadly classified into the following United States Department of Agriculture food groups: grains; nuts and seeds; soy products; and beans, peas, and lentils.

Results: We included 13 studies reporting on protein intake/sources that were conducted in the United States, Europe, and South Korea. Of these, 7 reported on vegan, 11 on vegetarian, 7 on pescovegetarian, and 7 on semivegetarian diets with total protein intake ranging from 10% to 17.4%. Vegan diets had the highest plant protein proportion (range: 77%-98%) and semivegetarian diets the lowest (range: 37%-83%). Plant protein source contribution was the highest from grains (range: 60%-78%). Nuts and seeds were the most consumed in vegetarian diets (7.9%; 2.9%-10.3%) and least in semivegetarian diets (3.7%; 2%-14.8%). Soy products and 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 semivegetarian (3.7%; 1.3%-13.9%, and 8.5%; 5.2%-10.2%) diets.

Conclusions: Vegan diets has the highest plant protein proportion and a variety of plant protein sources, while semivegetarian diets has the lowest plant protein proportion and mainly relied on grains as a plant protein source.