Dietary Protein and Amino Acids in Vegetarian Diets—A Review

Abstract

While animal products are rich in protein, the adequacy of dietary protein intake from vegetarian/vegan diets has long been controversial. In this review, we examine the protein and amino acid intakes from vegetarian diets followed by adults in western countries and gather information in terms of adequacy for protein and amino acids requirements, using indirect and direct data to estimate nutritional status. We point out that protein-rich foods, such as traditional legumes, nuts and seeds, are sufficient to achieve full protein adequacy in adults consuming vegetarian/vegan diets, while the question of any amino acid deficiency has been substantially overstated. Our review addresses the adequacy in changes to protein patterns in people newly transitioning to vegetarian diets. We also specifically address this in older adults, where the issues linked to the protein adequacy of vegetarian diets are more complex. This contrasts with the situation in children where there are no specific concerns regarding protein adequacy because of their very high energy requirements compared to those of protein. Given the growing shifts in recommendations from nutrition health professionals for people to transition to more plant-based, whole-food diets, additional scientific evidence-based communications confirming the protein adequacy of vegetarian and vegan diets is warranted.

Nutritional Quality of Vegetarian and Non-Vegetarian Dishes at School: Are Nutrient Profiling Systems Sufficiently Informative?

“…The protein contents were well above the 5%/100 kcal threshold for the three sub-categories of vegetarian dishes. In fact, protein deficiency is almost impossible with regard to children at primary school, even with vegetarian or vegan dishes, since the protein recommendation for children is relatively low compared to their energy needs [ 30 ]. The level of amino acids has not been estimated, but given that protein content is high, it can be assumed that amino acid requirements are easily met by vegetarian dishes, despite a less optimal distribution profile of amino acids in plant-based foods [ 30 ].…”

“…In fact, protein deficiency is almost impossible with regard to children at primary school, even with vegetarian or vegan dishes, since the protein recommendation for children is relatively low compared to their energy needs [ 30 ]. The level of amino acids has not been estimated, but given that protein content is high, it can be assumed that amino acid requirements are easily met by vegetarian dishes, despite a less optimal distribution profile of amino acids in plant-based foods [ 30 ]. Iron was present at an “adequate” level in vegetarian dishes, but with a necessarily lower content of haem iron (only present in animal-based foods, better absorbed and better available than non-haem iron) and, a higher content of non-haem iron than in non-vegetarian dishes.…”

The association between protein consumption from animal and plant sources with psychological distress in older people in the Mediterranean region

“…Typically, western-style diets increase production of inflammatory cytokines, and risk of cardiovascular and neurological conditions [12,44]. Plant-based proteins possess a cluster of nutrients which are anti-inflammatory, promote gut health, and are neuroprotective, including a range vitamins, minerals, plant bio actives including polyphenols, and fibre [2,58]. Animal proteins may displace plant foods in the diet, and when combined with processed foods can lead to poorer gut health [59].…”

“…The relationship between animal and plant-based protein sources is complex, and measurement of inflammatory biomarkers and sampling of the gut microbiota in omnivores and vegans and vegetarians in large cohorts will strengthen future research findings observing differences between protein sources. In addition, extensive studies including plasma or urine biomarkers of amino acid sufficiency, are required to further understand how crucial plantbased protein sources are to diet quality [58].…”

Probiotic administration increases amino acid absorption from plant protein – A placebo‐controlled, randomized, double‐blind, multicenter, crossover study

“…In addition, a reduction of animal protein intake, in particular meat consumption, has recently become more prevalent in Western countries. Protein intake is usually the highest in meat-eaters, followed by fish-eaters, lacto-ovo vegetarians, and vegans [16]. Insufficient protein intake from vegetarian diets may occur if the diets are low in protein-rich foods such as legumes, nuts, or seeds; however, there is currently no evidence that a balanced vegetarian diet provides inadequate total protein intakes [16].…”