Hydroxymethylbutyrate (HMB), a metabolite of the amino acid leucine, has been studied for its potential to prevent or reduce muscle wasting (cachexia) in various populations, including those with cancer, AIDS, or age-related muscle loss. Scientific evidence suggests that HMB supplementation can decrease muscle protein breakdown and promote muscle mass retention, especially in situations where muscle wasting is a concern.

Clinical studies, such as randomized controlled trials in elderly individuals and patients with chronic diseases, have shown that HMB supplementation (typically at 3 g/day) can help preserve lean body mass and improve muscle function. For example, a meta-analysis published in Clinical Nutrition (2015) reported that HMB supplementation was associated with modest increases in muscle mass and strength in older adults. Some studies in cancer or AIDS patients also indicate potential benefits, though results are mixed and often limited by small sample sizes or methodological differences.

While HMB is not universally endorsed as a standard therapy for muscle wasting, its use is supported by mechanistic studies (showing reduced protein degradation) and clinical trials demonstrating at least modest efficacy. However, the overall quality and quantity of evidence is moderate, and more large-scale, high-quality trials are needed to fully establish its role. Thus, the rating is 3/5 for scientific evidence supporting HMB's use in treating or supporting conditions involving muscle wasting.