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.

Keywords: adequacy; adults; amino acids; protein; protein intake; protein requirement; vegan diet; vegetarian diet.

Figure 1

Protein intake (g/day) in the Adventist Health Study 2. From Rizzo and collaborators [9] with permission.

Figure 2

Relative consumption of food groups (g) in low meat-eaters, poultry-eaters, fish-eaters, vegetarian, and vegan men compared to regular meat-eaters in the EPIC-Oxford study. The mean consumption relative to regular meat-eaters (1.00) is shown for each food group after adjustment for age. Circled are intakes of animal or plant-protein rich food groups. Adapted from [61].

Figure 3

Prevalence of protein and lysine adequacy (% of the INCA2 study population, n = 1678) in simulations of a reduction in animal protein intake by gradually balancing it against the same amount of energy from a replacement combination composed of plant foods already consumed by individuals and a mixture of legumes, nuts and seeds. For example, the “40%” curves show the protein and lysine inadequacy when substituting animal protein with a combination of 40% of protein from legumes, nuts and seeds, and 60% of plant protein from foods already consumed by the individuals. The filled area represents the 95% confidence interval. LNS: legumes, nuts and seeds. Reproduced with permission from the authors [57].