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HMB: no effect in human trial

Amateur bodybuilders with an average-sized wallet shouldn't bother buying HMB. They'll be better off spending their money on other products, sports scientists at Massey University in New Zealand conclude in an article soon to be published in the Journal of Strength and Conditioning Research. In the most extensive independent study done so far on HMB, the researchers tested this expensive nutritional supplement on a couple of dozen bodybuilders.

HMB, in full beta-hydroxy beta-methylbutyric acid [structural formula shown here], is produced by enzymes which convert the amino acid leucine in the body. HMB is then converted further in the muscle cells into raw materials for the production of cholesterol. Cholesterol is needed for the muscle cell membranes. When muscle cells are exposed to stress you can protect them from destruction by doing everything possible to stabilise the muscle membrane.

That's the HMB theory in a nutshell. The guys who discovered HMB have been promoting the amino acid as a bodybuilding supplement since the mid 90s. There's now an impressive pile of studies which show that bodybuilders gain strength and muscle mass if they take HMB. There's just one problem: most of the studies were done by the makers of HMB. Meanwhile they must have been doing pretty well for themselves. The stuff is expensive.

That's why the New Zealanders decided to do their own study on the effects of HMB in bodybuilders. The selected a couple of dozen subjects: men in their twenties who had been doing weight training for about four years. They trained in the gym three times a week for a bit longer than an hour each session. Half of the group were given a daily dose of three grams of HMB and the other half got a placebo. After nine weeks the researchers looked at the changes in strength and body composition.

Well, there was nothing to get you running to the supplement store. The figure below shows the effect of HMB on the 1RM for three different exercises.

HMB: no effect in human trial

The HMB users showed slightly more progression on the leg-extensions than the placebo users. But for the other exercises the results were the other way round.

There was hardly any effect on body composition, although it looks as though the HMB users lost 400 grams of fat while the placebo users gained 100 grams of fat. Not what you'd call significant effects.

HMB: no effect in human trial

Reviewing all their findings, the researchers conclude that HMB has little or no effect. "Small reductions in fat mass are possible with HMB and may be of interest to competitive body builders", they write. "For the average recreational resistance exerciser most concerned with fitness and health, the trivial (or, at best, small) possible benefits to body fat reduction, combined with the high cost of the supplement, suggest that HMB is of minor worth."

J Strength Cond Res. 2009 May;23(3):827-35.

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