Does HMB Increase Muscle Size and Strength?
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Does HMB Increase Muscle Size and Strength? |
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HMB, short for beta-hydroxy-beta-methylbutyrate, is a downstream metabolite of the branched-chain amino acid leucine and its ketoacid alpha ketoisocaproate (KIC). Advertisements for the supplement claim that HMB decreases muscle breakdown after exercise, speeds muscle repair, and increases muscle mass and strength during resistance training.
The claims of reduced muscle proteolysis and increased muscle size and strength are supported by only two studies (published together) by Stephen Nissen, PhD, DVM, and colleagues at Iowa State University in Ames (see Nissen, 1996). In the first study, 41 untrained male subjects (ages 19-29, average weight of 82.7 kg) were randomly divided into one of three groups receiving varying amounts of HMB – 0 (placebo), 1.5, or 3 grams per day. The subjects also ingested one of two different amounts of protein; either a normal level of 117 grams per day (1.4 grams per kg) or a high level of 175 grams per day (2.1 grams per kg). The subjects lifted weights for an hour and a half, three times a week for three weeks.
While not statistically significant, the HMB supplemented subjects tended to gain lean body mass in a dose-responsive manner -- 0.4 kg for the placebo group, 0.8 kg for the 1.5 gram HMB group, and 1.2 kg for the 3.0 gram HMB group. The level of protein intake did not influence body weight change or the amount of weight lifted for any of the exercises. However, the HMB supplemented subjects lifted more weight than the placebo group during all three weeks. The combined HMB groups performed significantly more abdominal exercises (a 50% increase) compared to the placebo group (a 14% increase). Total strength (upper and lower body) increased significantly in both the 1.5 gram HMB group (13%) and the 3.0 gram HMB group (18.4%), compared to the placebo group (8%). HMB improved lower body strength and abdominal strength more than upper body strength.
HMB supplementation was also associated with decreased biochemical indicators of muscle damage. Urinary 3-methylhistidine (3-MH) decreased by 20% and serum levels of muscle creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) fell by 20-60%. The results for the first study suggested that HMB can partially prevent exercise-induced proteolysis and/or muscle damage, thereby promoting greater gains in muscle mass and strength during a resistance-training program.
A second study was conducted to determine whether HMB supplementation would promote changes in body composition and strength over a longer time period (see Nissen, 1996). The 32 male trained subjects (ages 19-22, average weight of 99.9 kg) were randomly divided into two groups receiving either no HMB (placebo) or 3.0 grams of HMB per day. The subjects lifted weights for two to three hours daily, six days a week for seven weeks. By day 14 and through day 39, the HMB supplemented subjects gained significantly more fat free mass than the placebo group. On the last day of the study, fat free mass was not significantly different between the groups. However, HMB supplementation significantly increased bench press strength by almost threefold.
In a review article, Nissen and colleagues suggest that HMB, rather than leucine, is responsible for the well-known anticatabolic actions of leucine (see Nissen, 1997). Approximately 5% of the leucine metabolized by the body is converted to HMB, which provides 0.2 to 0.4 grams of HMB per day. The authors hypothesize that HMB supplies a source of beta-hydroxy-beta-methylglutaryl CoA (HMG Co-A) for cholesterol synthesis by the muscle cell. They propose that muscle cells can’t use blood cholesterol effectively and need to manufacture it internally. In stressful conditions, the muscle cells require greater cholesterol production for the synthesis of new cell membranes or to regenerate damaged membranes of existing cells. Thus, HMB may be important during periods of stress to promote increased muscle cell integrity and function.
The authors note that further data is needed to support this theory and that the exact mechanism behind HMB’s proposed effectiveness depends on future research. They further indicate that HMB is safe, does not cause adverse physiological or psychological effects, and does not alter any indicators of organ or tissue function.
Advertisements for the supplement recommend consuming 3 grams of HMB per day. The ads also suggest using a dietary supplement containing "pure" HMB, since it is extremely difficult to consume enough foods high in HMB (alfalfa, corn silage, grapefruit and catfish) to obtain the benefits. Lastly, the ads recommend against consuming leucine since 60 grams of leucine are required to obtain 3 grams of HMB. In addition to being impractical, this could cause severe gastrointestinal distress (see Environmental and Applied Sciences website: http://www.eas.com).
Athletes who weight train should not consider HMB a magic bullet. The following points should be considered before taking HMB supplements: 1) the results have not been reproduced by other researchers in other labs; 2) the subjects in the first study by Nissen and colleagues were untrained, so the results cannot be applied to trained individuals or elite athletes; 3) three weeks of HMB supplementation in untrained subjects did not significantly increase muscle mass compared to a placebo 4) seven weeks of HMB supplementation in trained subjects did not increase muscle mass compared to a placebo 5) HMB is expensive -- a ten day supply costs about $34.95; and 6) the Dietary Supplement and Health Education Act of 1994 allows products to be marketed without proof of safety, efficacy, or potency, so there is no guarantee of consistent dosage.
References
Nissen SL et al. Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training. Journal of Applied Physiology. 1996; 81(5):2095-2104.
Nissen SL et al. Nutritional role of the leucine metabolite beta-hydroxy-beta methylbutyrate (HMB). Journal of Nutritional Biochemistry. 1997; 8(June):300-311.
Ellen Coleman,
RD, MA, MPH
ellen@cruciblefitness.com
