Branched-chain amino acids (BCAAs), particularly leucine, have received growing research interest as nutritional strategies to preserve muscle mass in older adults. However, preclinical evidence has raised concerns that elevated BCAA exposure may adversely influence energy balance, appetite regulation and adiposity, with animal models demonstrating that high dietary BCAA concentrations relative to other amino acids, notably tryptophan, can induce hyperphagia and fat mass gain. Whether these concerns translate to body composition outcomes in older adults without sarcopenia remains unclear. This systematic review and meta-analysis was therefore conducted to address this gap.
Seven randomised controlled trials, including 288 participants were eligible for inclusion with intervention duration ranged from 6 to 24 weeks. No eligible trial examined complete BCAA supplementation, or considered ratios between BCAA and other amino acids, all interventions involved isolated leucine or leucine-enriched formulations. Random-effects meta-analyses showed no significant effect of supplementation on lean mass (MD: 0.06 kg, 95% CI: −0.16 to 0.27), fat mass (MD: 0.10 kg, 95% CI: −0.31 to 0.51), fat percentage (MD: −0.06%, 95% CI: −0.55 to 0.43), or body weight (MD: −0.43 kg, 95% CI: −1.50 to 0.63), with low to negligible between-study heterogeneity. For energy intake, the primary analysis suggested a non-significant result with substantial heterogeneity; however, sensitivity analysis excluding one influential study identified a significant reduction in energy intake with supplementation (MD: −175.85 kcal, 95% CI: −272.04 to −79.65).
These findings suggest leucine or leucine-enriched supplementation may provide limited additional benefit for body composition in aging populations without sarcopenia and do not support concerns about adverse effects on body weight or adiposity raised by preclinical evidence. Although sensitivity analysis suggested a reduction in energy intake, this finding should be interpreted cautiously, as lower energy intake in older adults may have implications for overall nutritional adequacy and muscle preservation.