HMB (Hydroxymethyl Butyrate)

Technically beta-hydroxy beta-methylbutyric acid, HMB is a chemical that occurs naturally in the body when the amino acid leucine breaks down. Leucine is found in particularly high concentrations in muscles. During athletic training, damage to the muscles leads to the breakdown of leucine as well as increased HMB levels. Evidence suggests that taking HMB supplements might signal the body to slow down the destruction of muscle tissue. However, while promising, the research record at present is contradictory and marked by an absence of large studies.

HMB is not an essential nutrient, so there is no established requirement. HMB is found in small amounts in citrus fruit and catfish. To get a therapeutic dosage, however, you need to take a supplement in powder or pill form.

A typical therapeutic dosage of HMB is 3 g daily. Be careful not to confuse HMB with gamma hydroxybutyrate (GHB), a similar supplement. GHB can cause severe sedation, especially when combined with other sedating substances, such as alcohol or antianxiety drugs.

According to most but not all of the small double-blind trials performed thus far, HMB may improve response to weight training. HMB might help prevent muscle damage during prolonged exercise.

Muscle Building Studies on chick and rat muscles suggest that HMB reduces the amount of muscle protein that breaks down during exercise. In a controlled study, 41 male volunteers aged 19 to 29 were given either 0, 1.5, or 3 g of HMB daily for 3 weeks. The participants also lifted weights 3 days a week for 90 minutes. The results suggested that HMB can enhance strength and muscle mass in direct proportion to intake. In another controlled study reported in the same article, 32 male volunteers took either 3 g of HMB daily or placebo, and then lifted weights for 2 or 3 hours daily, 6 days a week for 7 weeks. The HMB group saw a significantly greater increase in its bench-press strength than the placebo group. However, there was no significant difference in body weight or fat mass by the end of the study. Another double-blind placebo-controlled trial of 39 men and 36 women found that over a period of 4 weeks, HMB supplementation improved response to weight training. Two placebo-controlled studies in women found that 3 g of HMB had no effect on lean body mass and strength in sedentary women, but it did provide an additional benefit when combined with weight training. In addition, a double-blind study of 31 men and women, 70 years old, undergoing resistance training, found significant improvements in fat-free mass attributable to the use of HMB (3 g daily). However, other studies have found marginal or no benefits with HMB for enhancing body composition or strength. HMB may have greater effects on lean body mass and muscle strength when combined with creatine. All of these studies were small, and therefore, their results are not very reliable. Larger studies will be necessary to truly establish whether HMB is helpful for power athletes working to enhance strength and muscle mass.

HMB seems to be safe when taken at standard doses. Clinical trials have not found any significant adverse effects with short-term HMB use. Short and long-term toxicological studies in animals have also found no evidence of harm. However, full safety studies have not been performed, so HMB should not be used by young children, pregnant or nursing women, or those with severe liver or kidney disease, except on the advice of a physician. As with all supplements taken in very large doses, it is important to purchase a quality product, as an impurity present even in very small percentages could add up to a real problem.