Synopsis

Source of validity: Scientific
Rating (out of 5): 3

Synopsis: β-Hydroxy β-methylbutyrate (HMB), also known as Hydroxymethylbutyrate, is a bioactive metabolite of the amino acid leucine. Its use to support muscle health is primarily justified by scientific research. Several randomized controlled trials and meta-analyses have investigated HMB supplementation in various populations, including athletes, older adults, and individuals experiencing muscle wasting due to illness or inactivity.

Evidence suggests that HMB supplementation can help reduce muscle protein breakdown, especially in catabolic conditions, and modestly increase muscle mass and strength when combined with resistance training. For example, a 2015 meta-analysis in the Journal of Cachexia, Sarcopenia and Muscle found that HMB supplementation improved muscle mass and strength in older adults. Similarly, some studies in athletes have shown improvements in lean body mass and reductions in markers of muscle damage, although findings are mixed and often show small effect sizes.

Importantly, the greatest benefits are generally seen in populations at risk for muscle loss rather than in healthy, already well-trained individuals. The proposed mechanisms include stimulation of muscle protein synthesis (via mTOR pathway activation) and inhibition of muscle protein breakdown (attenuation of ubiquitin-proteasome pathway).

In summary, there is moderate scientific evidence supporting HMB’s role in preserving or enhancing muscle mass and function, particularly in specific populations. However, effects are modest, and optimal dosing and long-term safety require further research.

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