HMB (betahydroxy betamethylybutyrate)

What is it? HMB is short for betahydroxy betamethylybutyrate, which is found as a metabolite of the essential amino acid (protein fragment) leucine in our bodies and in small amounts in food.

How does it work? The exact mechanisms are poorly understood, but HMB seems to both help protein synthesis within muscle while simultaneously reducing the amount of protein breakdown or catabolism that occurs as a result of training (exercise induced muscle damage) allowing a more rapid return to protein synthesis. The net effect is to maximise muscle growth as a result of resistance training.

How strong is the evidence that it does what it's claimed to do? Like creatine, HMB is one of the very few sport supplements backed by scientific research. In fact, in a 2003 survey in the Journal of Applied Physiology (No.94; 2003) of all the scientific literature published between 1967 and 2001 examining 250 different sports supplements, only HMB and creatine were found to significantly increase muscle mass when judged against strict criteria.

Who can benefit from it? Anybody seeking to maximise muscle gain or minimise muscle loss (eg. trying to conserve muscle mass while dieting to lose body fat).

What are the drawbacks? None really (other than cost) although the same health warning applies as for creatine. Remember, since we don't know exactly how it works, we can't know exactly what it's doing.