Beta-hydroxy-beta-methylbutyrate (HMB)

Main functions

• Increases muscle mass.
• Reduces the amount of fatty tissue.
• Increases strength and power.

Theoretical foundations

Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the branched-chain amino acid leucine. Nissen et al. suggest that HMB is responsible for the well-known anticatabolic effects of leucine. HMB may partially prevent proteolysis and/or exercise-induced muscle damage, and thus promote gains in muscle mass and strength during resistance training.

Nissen et al. suggested that HMB is a precursor of beta-hydroxy-beta-methylglutaryl-CoA (HMB-CoA), which is involved in cholesterol synthesis by muscle cells. They believe that muscle cells cannot efficiently use cholesterol from the blood and must produce it themselves. Under stressful conditions, muscle cells require more cholesterol to synthesize new cell membranes or to regenerate damaged membranes of existing cells. Thus, HMB may be important during periods of stress, such as resistance exercise, to enhance muscle cell integrity and function. Further research is needed to confirm this theory and clarify the mechanism of action of HMB.

Research results

The findings of reduced muscle proteolysis and increased muscle mass and strength have been confirmed by only two published studies at the University of Iowa at the same time. The first study involved 41 untrained men (ages 19-29, average body weight 82.7 kg). The subjects were randomly divided into three groups, which were given varying amounts of HMB-0.5 g (placebo), 1.5 g, or 3.0 g per day. In addition, they were also given one of two protein doses: either a normal dose of 117 g per day (1.4 g-kg1) or a higher dose of 175 g per day (2.1 g-kg1). The subjects lifted weights for 1.5 hours three times a week for three weeks.

Subjects receiving HMB supplements showed a body weight gain corresponding to a dose of 0.4 kg for the placebo group, 0.8 kg for the 1.5 g HMB group, and 1.2 kg for the 3.0 g HMB group. Protein intake had no effect on changes in body weight or the amount of weight lifted. However, subjects receiving HMB supplements lifted more weight than those receiving placebo for 3 weeks. The HMB supplement group performed significantly more abdominal exercises (50%) than the placebo group (14%). Total strength (upper and lower body) increased significantly in both groups: 13% in the 1.5 g HMB group and 18.4% in the 3.0 g HMB group; In the placebo group, this value was 8%. When taking GMB, the muscle strength of the lower body is greater than that of the upper body.

With the use of GM B, muscle damage is reduced. In urine, 3-methylhistidine (3-MG) decreased by 20%, and in serum, the activity of muscle creatine phosphokinase (CrPK) and lactate dehydrogenase (LDH) decreased by 20-60%.

The second study examined the effects of HMB supplementation on changes in body composition and muscle strength over a longer period of time: 32 resistance-trained men (ages 19-22, average body weight 99.9 kg) were randomly assigned to receive either a placebo or 3.0 g HMB per day. Subjects lifted weights for 2-3 hours daily, 6 days per week for 7 weeks. From day 14 through day 39, subjects receiving HMB supplementation significantly increased lean mass compared to those receiving placebo. On the final day of the study, lean mass did not differ significantly between groups.

Recommendations

Athletes should not consider GMB a magic wand. Two studies were conducted by the same research group that developed GMB. The results of the studies are interesting, but they should be analyzed seriously first.

Before using HMB supplements, the following questions should be considered.

• The results have not been repeated by other researchers in other laboratories.
• The subjects in the first study by Nissen et al. were untrained, so the results may not apply to trained individuals or elite athletes.
• Three weeks of GMB supplementation in untrained subjects increased muscle mass slightly compared to the placebo group.
• Seven weeks of HMB supplementation in trained subjects did not increase their muscle mass compared to a placebo group.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ]