Evidence Level
HMB (Beta-Hydroxy Beta-Methylbutyrate) is a well-researched compound supported by numerous human studies. A 2003 meta-analysis of nine studies involving 1,300 participants demonstrated that HMB supplementation significantly enhances lean mass and strength gains in untrained individuals during resistance exercise (Nissen & Sharp, 2003). However, its benefits for well-trained athletes are minimal during regular training.
Key findings highlight HMB's anti-catabolic properties. A 2015 systematic review and meta-analysis of seven randomized controlled trials involving older adults found that HMB supplementation significantly increased muscle mass compared to control groups (Wu et al., 2015). Additionally, a 2018 study revealed that HMB free acid alters cortisol responses during a 24-hour fast but does not affect muscle protein breakdown (Tinsley et al., 2018).
HMB has also shown benefits in clinical populations. A 2016 randomized controlled trial demonstrated that combining pulmonary rehabilitation with an HMB-enriched supplement improved body composition and health-related quality of life in patients with bronchiectasis (Olveira et al., 2016). Furthermore, a 2015 study comparing bioavailability found that HMB free acid has superior absorption compared to calcium salt forms, with higher plasma clearance rates and peak concentrations (Fuller et al., 2015).
In summary, while HMB may not significantly enhance muscle-building in experienced athletes, it is effective in preventing muscle loss during periods of stress, such as aging, illness, or caloric restriction.