HMB's Use In Athletics

HMB, or "beta-hydroxy beta-methylbutyrate", is a metabolite of the amino acid Leucine and is produced naturally by the human body. HMB is produced from a metabolite of leucine, called ketoisocaproate (KIC), by the enzyme KIC-dioxygenase.

You may have first heard of HMB during the summer Olympics of 1996 when American swimmers were quoted in newspaper articles as saying, "they had benefited from using HMB during their training".

Steven Nissen and his colleagues have performed the only study to date of HMB on humans. The researchers agree that the mechanism by which HMB impacts muscle proteolysis and function is not currently known. Nevertheless there are a number of postulations. "The high substrate concentration required by the dioxygenase enzyme compared with the liver concentration of KIC suggests that HMB production in the body may be a first-order reaction controlled by enzyme and KIC concentrations. It has been calculated that, under normal conditions, about 5% of leucine oxidation proceeds via this pathway. Therefore, if humans are assumed to have enzyme actions similar to those seen in pigs, a 70-kg human would produce from .2 to .4 g HMB/day depending on the level of dietary leucine. At leucine intakes of 20-50 g/day (which are used therapeutically), the concentrations of leucine and KIC in the liver increase and could result in HMB production reaching gram quantities per day". Some studies involving HMB supplementation to the diet of steers and pigs have been shown to improve caracass quality. Based on these findings, it has been hypothesized that supplementing the diet with HMB may inhibit protein degradation during periods of increased proteolysis such as resistance training.

Companies who promote the product claim that humans neither produce enough HMB in their bodies, nor do they eat such HMB-containing foods (e.g. catfish and grapefruit) regularly enough to provide the full benefits of HMB. Researchers claim that when we input extra amounts of HMB into our bodies the metabolite acts as a performance enhancer for such activities as weight lifting and sprinting. In effect, companies claim that HMB boosts strength levels, enhances gains in muscle size and strength, and prevents post-workout muscle tissue breakdown. The marketing companies do not make exactly clear how the product works, but they have formulated a few widely accepted ideas which are seen on the advertisement postings in many nutritional stores. Many of them believe that excess amounts of HMB in the body cause an interference with the body?s natural process of protein breakdown (particularly after a workout).

Due to the fact that a limited number of HMB studies have been performed on humans, we must also consider the results of the tests on animals. Perhaps there is a connection between the noted improvements in the two animal tests and those of humans. This data alone, however, is insufficient. Since HMB is a relatively new product, one must take into consideration the possible side effects or other negative aspects of upsetting a natural balance within the body.

The patent for HMB use as a sport supplement is owned by Iowa State University Research Foundation (ISURF) and has been licensed to Metabolic Technologies, Inc. under U.S. patent number 5,348,979. If you come across an HMB supplement that doesn't have this patent number on its label, don't buy it. It's very likely fake. This does not mean that an HMB product that doesn't have the patent number on the label is certainly counterfeit. The current patents protect the nutritional uses of HMB for promoting nitrogen retention and the explanation of those methods. These "use" patents do not prevent others from manufacturing HMB, it just prevents them from saying their products improve nitrogen retention and muscle growth. However, because HMB is not a simple nutrient to manufacture, in all likelihood any product that doesn't have the patent #5,348,979 is fraudulent.

In terms of safety, a number of animal species have been fed large amounts of HMB for varying periods of time. In all the animal studies, there were no adverse effects or increases in death rates. When animals were autopsied, there were no pathological changes in their organs or tissues. Instead, the investigators found a lowered LDL (bad cholesterol) response, increased immune function, fewer respiratory illnesses, more lean body mass, and reduced fat mass. Even when pigs were fed 100 times that used by humans, no problems occurred.

In human studies using 2-5 grams of HMB, blood chemistry, liver function, and kidney function all remained normal. All the human studies that looked at cholesterol found an average LDL decrease of 7%.

Nutritional strategies of overfeeding, ingesting carbohydrate/protein before and after exercise, and dietary supplementation of various nutrients [e.g. protein, glutamine, branched-chain amino acid, creatine, leucine, beta-hydroxy beta-methyl-butyrate (beta-HMB), chromium, vanadyl sulfate, boron, prasterone (dehydroepiandrosterone [DHEA]) and androstenedione] have been purported to promote gains in fat-free mass during resistance training. Most studies indicate that chromium, vanadyl sulfate and boron supplementation do not affect muscle growth. However, there is evidence that ingesting carbohydrate/protein prior to exercise may reduce catabolism during exercise and that ingesting carbohydrate/protein following resistance-exercise may promote a more anabolic hormonal profile. Furthermore, glutamine, creatine, leucine, and calcium beta-HMB may affect protein synthesis. Creatine and calcium beta-HMB supplementation during resistance training have been reported to increase fat-free mass in athletic and nonathletic populations.

  • Nic Vera. HBM: A Dietary Supplement for Building Muscle? Vanderbilt University
  • Nissen S; Sharp R; Ray M; Rathmacher JA; Rice D; Fuller JC Jr; Connelly AS; Abumrad N, "Effect of Leucine Metabolite Beta-Hydroxy-Beta-Methylbutyrate on Muscle Metabolism During Resistance-Exercise Training" Journal of Applied Physiology (November 1996): 2095-2104
  • Nissen and Abumrad, Nutritional role of the leucine metabolite ß-hydroxy ß-methylbutyrate (HMB). J. Nutri. Biochem. 8:300-311, 1997.
  • Kreider RB. Dietary supplements and the promotion of muscle growth with resistance exercise. Sports Med 1999 Feb;27(2):97-110. Department of Human Movement Sciences and Education, University of Memphis, Tennessee, USA.

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