Background: High-protein diets have been shown to improve body composition through alterations in satiety, muscle protein synthesis, and the thermic effect of food.
Aim: Given these findings, the purpose of this review is to discuss the integration of the specific hormonal and metabolic effects of high-protein diets following both acute and long-term usage, especially with regard to body composition.
Methods: Full-text articles were obtained through PubMed by using the terms "high-protein diet and body composition," "high-protein diet and exercise," "high-protein diet risk," "high-protein diet side effects," "protein quality PDCAAS," "RDA for protein," and "daily protein recommendation." Articles were initially screened according to their title and abstract; careful evaluation of the full manuscripts was then used to identify relevant articles.
Results: The higher satiety exerted by high-protein diets is generated through increments in anorexigenic, as well as decrements in orexigenic hormones. Improvements in muscle mass are achieved by activation of muscle protein synthesis acting through the mTOR pathway. High thermic effect of food is caused due to necessary deamination, gluconeogenesis, and urea synthesis caused by high-protein diets. Interestingly, high-protein diets in both hypo- and normocaloric conditions have shown to improve body composition, whereas in combination with hypercaloric conditions does not seem to increase fat mass, when the excess energy comes from protein.
Conclusions: High protein diets effectively improve body composition by acting through different pathways.
Keywords: PDCAAS; Protein; acute effects; chronic effects; exercise; high-protein diet; leucine; safety; sex differences; side effects.