Effects of Protein and Amino Acid Supplementation on Muscle Mass and Strength in a Healthy Population

The objective of this study was to investigate the effect of protein and/or amino acid supplementation on muscle mass and strength in a healthy population. A structured literature search was conducted from database inception up to October 23, 2019, using PubMed and Scopus. Data were collected from randomized controlled trials and weighted mean difference, and its 95% confidence interval was calculated by using a random-effects model. Risk of bias was assessed using the Cochrane tool. Data were included from 46 randomized controlled trials, totaling 2049 participants. Protein but not amino acid supplementation resulted in significant positive effects on muscle mass (weighted mean difference, 0.47 kg; 95% confidence interval, 0.18-0.75 kg; P <.001) and upper body strength. The significant effect of protein supplementation on muscle mass persisted in the subgroups with and without resistance training, in young (<30 years) and older (≥59 years) adults, and across either gender. This review suggests that dietary protein and/or amino acid supplementation may promote muscle mass hypertrophy and/or maintenance, as well as some measures of muscular strength in a healthy population.