BCAA supplements added little to resistance training

Sarcopenia — age-related loss of muscle — erodes the ability to look after oneself, so anything that reinforces training is worth testing. Branched-chain amino acids, and leucine in particular, are known drivers of muscle protein synthesis, and resistance training is the most reliable stimulus for muscle growth. That combination has an obvious logic to it, and supplements are widely marketed on exactly that reasoning. What has been unclear is whether the two together add up to more than training alone in people who already have sarcopenia.

The authors searched four databases for randomised controlled trials pairing resistance training with BCAA-rich nutritional supplementation in older adults with sarcopenia. Twelve randomised trials, totalling 459 participants, met the criteria. Outcomes covered both body composition and physical function: skeletal muscle index, total lean mass, fat mass, hand grip strength, knee extension strength, walking speed, the 30-second chair stand and the Short Physical Performance Battery. Effects were pooled as standardised mean differences using random-effects models in Stata 18.0.

Only one outcome reached statistical significance: skeletal muscle index favoured the combined intervention (SMD 0.337, 95% CI 0.035 to 0.639, p = 0.029), with the lower bound sitting only just above zero. Everything else was non-significant, including hand grip strength (SMD 0.289, p = 0.080), the 30-second chair stand (SMD -0.794, p = 0.169), SPPB (SMD -0.321, p = 0.124), walking speed (SMD 0.344, p = 0.283) and knee extension strength (SMD 0.332, p = 0.328). Body composition beyond muscle index was flat: total lean mass (SMD 0.024, p = 0.908) and fat mass (SMD -0.036, p = 0.866) barely moved. The authors conclude the combination raised muscle index without improving function.

The mechanistic case for BCAAs is well established at the level of muscle protein synthesis, and this analysis does not dispute it — it questions whether that translates into strength and mobility when training is already in place. A small change in a muscle index measure without matching gains in grip, gait speed or chair-stand performance is a familiar pattern in nutrition trials, where composition markers shift more readily than function. Total lean mass not moving alongside muscle index is itself a puzzle these data leave open. Larger trials with longer follow-up and standardised dosing would be needed to know whether functional benefit emerges later.

This is a reason to treat BCAA supplements as a marginal addition rather than a lever, at least for older adults with sarcopenia who are already resistance training. The training itself remains the intervention with the robust evidence behind it in this population. Where a body composition marker improves but grip strength and walking speed do not, the practical gain is uncertain. Anyone weighing the cost of supplements against the evidence can reasonably note how thin the functional signal was here.