Β-Hydroxy β-methylbutyric acid

β-Hydroxy β-methylbutyric acid (HMB), otherwise known as its conjugate base, β-hydroxy β-methylbutyrate, is a naturally produced substance in humans that is used as a dietary supplement and as an ingredient in certain medical foods that are intended to promote wound healing and provide nutritional support for people with muscle wasting due to cancer or HIV/AIDS. In healthy adults, supplementation with HMB has been shown to increase exercise-induced gains in muscle size, muscle strength, and lean body mass, reduce skeletal muscle damage from exercise, improve aerobic exercise performance, and expedite recovery from exercise; in trained and competitive athletes, evidence is mixed on whether it meaningfully augments resistance training–induced gains in lean mass and strength. Medical reviews and meta-analyses indicate that HMB supplementation also helps to preserve or increase lean body mass and muscle strength in individuals experiencing age-related muscle loss. HMB produces these effects in part by stimulating the production of proteins and inhibiting the breakdown of proteins in muscle tissue. No adverse effects from long-term use as a dietary supplement in adults have been found.

The effects of HMB on human skeletal muscle were first discovered by Steven L. Nissen at Iowa State University in the mid-1990s. As of 2018, HMB has not been banned by the National Collegiate Athletic Association, World Anti-Doping Agency, or any other prominent national or international athletic organization. In 2006, only about 2% of college student athletes in the United States used HMB as a dietary supplement. As of 2017, HMB has reportedly found widespread use as an ergogenic supplement among young athletes.

Uses

Available forms

HMB is sold as an over-the-counter dietary supplement in the free acid form, β-hydroxy β-methylbutyric acid (HMB-FA), and as a monohydrated calcium salt of the conjugate base, calcium β-hydroxy β-methylbutyrate monohydrate (HMB-Ca, CaHMB). Since only a small fraction of HMB's metabolic precursor, L-leucine, is metabolized into HMB, pharmacologically active concentrations of the compound in blood plasma and muscle can only be achieved by supplementing HMB directly.