β-Hydroxy β-methylbutyric acid (HMB) is a naturally produced substance in humans that is used as a dietary supplement. It is 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 reduce skeletal muscle damage from exercise, expedite recovery from exercise, and increase exercise-induced gains in muscle size, muscle strength, and lean body mass. 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 protein production and inhibiting protein breakdown in muscle tissue. Pharmacologically active concentrations of the compound in blood plasma and muscle can only be achieved by supplementation with HMB. (Full article...)