The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: a systematic review and meta-analysis

In the present study. we performed a meta-analysis to assess the ability of leucine supplementation to increase the muscle protein fraction synthetic rate and to augment lean body mass or leg lean mass in elderly patients. A literature search was conducted on Medline, Cochrane, EMBASE and (bugle Scholar database up to 31 December 2013 for clinical trials that investigated the administration of leucine as a nutrient that affects muscle protein metabolism and muscle mass in elderly subjects. The included studies were randomised controlled trials. The primary outcome for the meta-analysis was the protein fractional synthetic rate. Secondary outcomes included lean body mass and leg lean mass. A total of nine studies were included in the meta-analysis. The results showed that the muscle protein fractional synthetic rate after intervention,significantly increased in the leucine group compared with the control group (pooled standardised difference in mean changes 1.08, 95% CI 0.50, 1.67, P<0.001). No difference was found between the groups in relation to lean body mass (pooled standardised difference in mean changes 0.18, 95% CI -0.18, 0.54; P=0.318) or leg lean mass (pooled standardised difference in mean changes 0.006, 95% CI -0.32, 0.44; P=0.756). These findings suggest that leucine supplementation is useful to address the age-related decline in muscle mass in elderly individuals, as it increases the muscle protein fractional synthetic rate.