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.
Highlights
Human dietary patterns range substantially in the degree of inclusion vs. avoidance of animal-based foods
When we modeled the isoenergetic replacement of animal protein foods with different types of plant protein foods and mixes in the French adult population, we found that some substitution scenarios that consisted of replacing animal protein with the current cereal-based plant protein intake resulted primarily in increasing the risk of an insufficient intake of total protein rather than of individual amino acids such as lysine—the risk of inadequacy of the latter always lagging well behind that of the former [57]
An insufficient protein intake from vegetarian diets may occur if the diet does not include protein-rich foods such as legumes and nuts and seeds, or any protein analogs of animal foods, the availability of which is increasing along with the proportion of people shifting their protein intake towards more plant protein sources
Summary
Human dietary patterns range substantially in the degree of inclusion vs. avoidance of animal-based foods. Study 2 (AHS-2), the protein intake of lacto-ovo-vegetarians and vegans were strikingly similar to those of fish-eaters, semi-vegetarians and non-vegetarians [9] (Figure 1) This difference from other populations may be explained by either of two reasons. We observed that the gradient for protein intake across the vegetarian spectrum is likely due to a high animal protein intake on a background western diet; those transitioning to vegetarian diets from high-animal protein western diets may choose lower protein plant foods compared to those culturally accustomed to more traditional plant-based diets. This point will be discussed in further detail below
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