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Hydroxymethyl Butyrate (HMB)
What is it? Overview Usage Side Effects and Warnings

What is Hydroxymethyl Butyrate (HMB)?

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.

According to some but not all of the small double-blind trials performed thus far, HMB may improve response to weight training. 2 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 ; 3 however, a follow-up study failed to find this benefit. 4 A very small study found evidence that HMB might improve aerobic exercise capacity. 5 Very weak evidence suggests that HMB might improve blood pressure and cholesterol levels. 6

Safety Issues

HMB seems to be safe when taken at standard doses. 7 Clinical trials have not found any significant adverse effects with short-term HMB use. 8 Short- and long-term toxicological studies in animals have also found no evidence of harm. 9 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.