Hydroxymethyl Butyrate (HMB) Overview

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. ¹ 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 anti-anxiety drugs.

In a controlled study, 41 male volunteers age 19 to 29 years old were given either 0 g, 1.5 g, or 3 g of HMB daily for 3 weeks. ² The participants also lifted weights 3 days a week for 90 minutes. The results suggest 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.

Similarly, a 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. ³ 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. ⁴ 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). ⁵ However, other small studies have found marginal or no benefits with HMB for enhancing body composition or strength. ⁶ When the results of small studies contradict one another, it often means that the studied treatment produces minimal benefits at most, and this may be the case with HMB. Larger trials will be necessary to truly determine the extent of its effect.

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