Oct. 10, 2000 -- Beta-hydroxy-beta-methylbutyrate -- with a name like that, you'd expect it to do something scientific. Better known as HMB, this substance, which is found in many protein supplements downed by gym rats, even has the OK of the folks on the International Olympic Committee. They categorize it as a legal substance that does not infringe on existing doping laws, and say it appears to have no harmful effects.
"Well, the International Olympic Committee tends to allow things that haven't been shown to work," Mark Juhn, DO, says with a laugh. "So I think their attitude is, 'Well, if you want to take something that hasn't been proven to work, go ahead.'" Juhn is a family and sports medicine doctor at the University of Washington in Seattle.
But does HMB, which is touted as being able to enhance gains in strength and lean muscle mass, really work? A review of studies of the supplement, recently published in the journal Sports Medicine, indicates that it may have a small effect -- but only on untrained athletes just starting a strength-training program. And many experts, including Juhn, are skeptical of its effectiveness.
"HMB has not been regarded as garnering much acceptance in the medical literature and amongst sports medicine professionals as being very convincing [for muscle building]," Juhn tells WebMD. "It definitely does not have very convincing data."
Juhn explains that HMB is a substance formed naturally when the body breaks down the amino acid leucine. Amino acids are the building blocks of protein, and proteins are the building blocks of muscle. "To make muscle, your body has to undergo what is called protein synthesis," Juhn says.
"The idea is that, theoretically, if you ingest your amino acids, you'll be able to increase protein and increase muscle mass," Juhn says. "But the other theory with it is that you can also help reduce the amount of muscle breakdown [caused by strength training] if you take the amino acids." This theory is problematic, though, because building new muscle requires some breakdown of protein within the muscle tissue, he says.
The new review, by a pair of Australian researchers, looked at the available information on HMB. From what the authors found, they suggest that HMB seems to work primarily in the untrained athlete during resistance training. The authors of the review, Gary J. Slater and David Jenkins, hail from the Australian Institute of Sport in Canberra and the University of Queensland in Brisbane, respectively.
One study in untrained individuals -- the 1996 research by Stephen L. Nissen, PhD, and colleagues that is often cited in supplement ads -- suggests that while even a placebo, or dummy pill, allowed participants to increase the total load they could lift by 8%, HMB did better. A 1.5-gram daily dose and a 3-gram daily dose showed a 13% and 18.4% increase, respectively. Lean tissue also seemed to increase, in the same dose-response manner. But "doses of HMB greater than 3 g/day do not appear to further enhance its effects on untrained individuals," Slater and Jenkins write.
Slater and Jenkins also report that the supplement doesn't appear to work so well -- if at all-- in trained athletes, or for experienced strength trainers in general.
Another study published by Nissen and colleagues in the Journal of Nutrition this year -- which was not included in the Sports Medicine review -- tested both trained and untrained people and found that HMB appeared to be helpful. But Juhn points out that this particular study was funded by Metabolic Technologies, a maker of HMB supplements.
And if you think you can forgo resistance training and build muscle just by taking this supplement or any others -- forget about it. "HMB does not appear to influence body composition in the absence of the stimulus provided by resistance training," the review authors write. They also reviewed studies that looked at HMB's use in older people and didn't see much effect. Nor did there seem to be a difference in the way males or females responded to the supplement.
Juhn says Sports Medicine is renowned for extensive, well-done reviews of studies and for giving good overviews of research. He says that includes this article, which he commends particularly for listing all the studies that the researchers reviewed and showing that only two were full published studies. The rest of the "evidence" -- six other studies of the efficacy of HMB -- have been published only in an abstract, or rough-draft form.
"We don't put much credence in abstracts," Juhn says.