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.

Therapeutic Dosages

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.

Therapeutic Uses

According to some but not all of the small double-blind trials performed thus far, HMB may improve response to weight training. 2-9,21,24,25]]> One small double-blind, ]]>placebo-controlled]]> trial found hints that HMB might help prevent muscle damage during prolonged exercise, thereby potentially ]]>enhancing recovery during athletic training]]> ; ]]>10]]> however, a follow-up study failed to find this benefit. ]]>25]]> A very small study found evidence that HMB might improve aerobic exercise capacity. ]]>26]]>

Very weak evidence suggests that HMB might improve ]]>blood pressure]]> and ]]>cholesterol]]> levels. ]]>18]]>


What Is the Scientific Evidence for Hydroxymethyl Butyrate?

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. 12]]> 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. ]]>13]]>

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. ]]>14 ]]>  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). ]]>15]]>

However, other small studies have found marginal or no benefits with HMB for enhancing body composition or strength. ]]>16,17,22,23,26]]>

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.


Safety Issues

HMB seems to be safe when taken at standard doses. 18]]> Clinical trials have not found any significant adverse effects with short-term HMB use. ]]>19]]> Short- and long-term toxicological studies in animals have also found no evidence of harm. ]]>20]]> 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.