Most people involved with sports nutrition and sports nutrition supplements has heard or read about Beta-hydroxy beta-methyl-butyrate or HMB for short. HMB appears to be one of those classic supplements that looks great in the lab but has had a rocky track record with "real world" users. Let me back up a moment.

HMB is actually a metabolite of the amino acid L-leucine. L-leucine is one of three amino acids known as the branched chain amino acids or BCAA (isoleucine and valine being the other two).

It has been known for a long time that BCAA play a critical role in the turn over of lean body tissues (muscle) and is muscle sparing (i.e. anti-catabolic) in a variety of muscle wasting states. Of the three BCAA, L-leucine appears to be the most important to preserving hard earned muscle mass and intense exercise and certain disease states have been shown to eat up a great deal of L-leucine. So far so good!

The main drawback of L-leucine is the fact that you must use large amounts of this amino acid to get a positive effect making it both expensive and impractical. Many studies that showed benefits were in fact done intravenously and used as much as 5 grams per hour of L-leucine!

That my friend is a lot of leucine.

So, it was theorized there might be a metabolite of this ultra important amino acid that was responsible for many of the positive effects of L-leucine but could be taken in far lower doses and by mouth (as opposed to having a tube stuck in your arm). That metabolite appears to be HMB.

Animal research with HMB has been impressive. During stressful conditions, animals will often lose weight and/or become quite ill. Some even die. This of course can be quite expensive for any company trying to make a living from these animals in one way or another. When animals were fed HMB they found a large reduction in mortality rates, increases in muscle mass, and improvements in immune function in the animals fed HMB.

Several studies in humans have also looked promising. Studies using both trained and untrained subjects found increases in muscle and decreases in bodyfat in people ingesting just three grams (3000mg) of HMB per day.

The average was approximately 2-4 pounds of muscle put on with an equal amount of fat taken off over a four week period. The scientists also found that HMB positively affected several biochemical markers of intense exercise that would lead one to believe that there was a reduction of muscle wasting in people taking HMB. "So what's the problem," you ask? The problem has been mainly that what looked so promising in the research has not been fully realized in the real world, hence my introduction to this section.

Several follow up studies with HMB in people also failed to find any results. Feed back from real world users has been generally negative with HMB. Some seem to feel they have benefited from it while most found HMB a big waste of money.

Were the studies that found benefits flawed? Are some people not taking enough? Does it depend on the nutritional status of the person using it and/or how they train?

It's not known for sure at this time, but considering the costs of HMB and the fact there are other less expensive alternatives that clearly work (i.e., creatine) I see no reason for hard working athletes to spend money on HMB until a definitive answer can be found. At this time, HMB gets a thumb's down for building muscle, but if you want to give it a try, I will not hold it against you ©

Mortimore, G.E., and A. R. Poso, et al. "Multiphasic Control of Hepatic Protein Degradation by regulatory Amino Acids, General Features and Hormonal Modulation," Journal of Biological Chemistry 262 (1987), p 16322-16327.

Flakoll, P.J. and M. J. VandeHaar, et al. "Influence of alpha-Ketoisocaproate on lamb Growth," Journal of Animal Science 69/4 (1991), p. 1461-1467.

Van Koevering, M. and Nissen, S. "Oxidation of Leucine and Alpha-Ketoisocaporate to B-hydroxy B-methylbutyrate In Vivo (Abstract)," American Journal of Physiology 261/1 (1992).

Nonnecke, B. J., Franklin, S. T. and Nissen, S. "Leucine and its Catabolites alter mitogen-stimulated DNA synthesis by bovine lymphocytes," Journal of Nutrition 121/10 (1991), p. 1665-1672.

Buckspan, R. B., and E. Hoxyworth. "Alpha-Ketoisocaproate is superior to Leucine in sparing muscle glucose during progressive fasting in normal male volunteers," American Journal of Physiology 251 (1983), p. E648-E653.

Nair, K.S., R. G. Schwarts and S. Wells. "Leucine as a regulator of whole body and skeletal muscle protein metabolism in humans," American Journal of Physiology 263 (1992), p. E928-934.

Chua, B., D. L. Siehle and H. E. Morgan. "Effects of Leucine and Metabolites of Branched Chain Amino Acids on protein turnover in heart," Journal of Biological Chemistry 254 (1979), p. 8358-8362.

May, M. E. and M. G. Buse. "Effects of branched chain amino acids on protein turnover," Diabetes Metab. Rev 5/3 (1989), p. 227-245.

Talleyrand, V. and A. Dorn, et al. "Effects of feeding B-hydroxy B-methylbutyrate on immune function in stressed calves," FASEB Journal 8 (1994), p. A951.

Nissen, S. and Morrical, D., et al. "The effects of the leucine catabolite B-hydroxy B-methylbutyrate on the growth and health of growing lambs," Journal of Animal Science 77 (1994), p. 243.

Van Koevering, M.T., H. G. Dolezal and et al. "Effects of ß-hydroxy ß-methylbutyrate on performance and carcass quality of feedlot steers," Journal of Animal Science 72 (1994), p. 1927-1935.

Nissen, S. and J. Panton, et al. "Effects of ß-hydroxy ß-methylbutyrate (HMB) supplementation on strength and body composition of trained and untrained males undergoing intense resistance training," Experimental Biology Conference Presentation Abstract (1996).

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