Background Information
This compound (a metabolite of the amino acid leucine) is readily available as a dietary supplement and reportedly widely used by athletes because of its proposed anti-catabolic effects on skeletal muscle. Some animal data can be found in support of this effect and one recent study indicated that HMB in combination with the amino acids glutamine and arginine can promote muscle mass gains in as little as 8 weeks in HIV patients. However, other animal studies show no effects of HMB on protein metabolism and some data even suggest that gains in body mass with HMB are due to increases in muscle fat not lean mass. The scientific data in humans are somewhat scarce and conflicting. Perhaps more convincing than its effects on muscle growth is the potential of HMB to enhance immune function.

 Recommendation
Although there are no data indicating its use could be harmful, insufficient information is available to evaluate fully whether or not HMB might cause adverse effects especially with prolonged use. Consequently, any recommendation for the use of HMB in athletes is premature at this time.