Beta-Hydroxy beta-methylbutyrate (HMB) is a metabolite of the amino acid leucine and has been studied for its effects on muscle mass, strength, and recovery, particularly in the context of resistance training and muscle wasting conditions. Multiple randomized controlled trials and meta-analyses have demonstrated that HMB supplementation can reduce muscle protein breakdown, promote muscle mass retention, and enhance strength gains, especially in populations at risk for muscle loss, such as older adults or those experiencing muscle wasting due to illness or inactivity.

HMB appears to exert its effects by stabilizing muscle cell membranes, reducing proteolysis (muscle protein breakdown), and possibly enhancing muscle protein synthesis. The benefits in healthy, trained athletes are more modest but still present, particularly during periods of high training stress or caloric restriction. The European Food Safety Authority (EFSA) and other regulatory bodies recognize HMB as safe for human consumption. However, the magnitude of benefit in already well-trained individuals may be less pronounced compared to those who are untrained or at risk of muscle loss.

Overall, the scientific evidence supports the use of HMB to support the muscles body system, particularly for muscle preservation and recovery. The evidence rating is not a perfect 5 because while the effects are statistically significant, they are sometimes modest and context-dependent.