The Influence of Vegan, Vegetarian, and Omnivorous Diets on Protein Metabolism: A Role for the Gut–Muscle Axis?

There has been a growing interest globally in vegan and vegetarian diets over the last decade for a combination of health, ethical, environmental, spiritual, and social reasons. In line with this popularity, research examining the role of plant-based food sources, including vegan and vegetarian diets, in supporting skeletal muscle remodeling and anabolism in humans has also received considerable attention. The emergence of the microbiota-gut–muscle axis, a bidirectional pathway where the gut microbiota impacts skeletal muscle and vice versa, has been suggested as a potential mediator of food and nutrition’s influence on the mechanistic processes that regulate muscle mass and function. Considering inherent nutritional differences between vegan, vegetarian, and omnivorous diets related to the fiber and macronutrient content, presence of anti-nutritional factors, and diverse food and supplemental sources for obtaining protein, it stands to reason that the regulation of the microbiota–gut–muscle axis via diet-induced changes in gut microbiota composition and function may be dissimilar. However, whether this translates into differential effects on the skeletal muscle is unclear. This review article aims to provide a contemporary perspective for how variations in gut microbiota linked to vegan, vegetarian, and omnivorous diets may be a potential mechanism for influencing protein metabolism in skeletal muscle mass via a purported microbiota-gut–muscle axis.