HMB stands for β-hydroxy-β-methylbutyrate, a byproduct (metabolite) of the breakdown of the amino acid leucine. HMB is produced naturally by the body and can also be gotten through dietary measures, however the amount necessary for an improved body exceeds the amount a reasonable person would get through diet alone. Because of this, the HMB supplement is popular among body builders and those trying to gain lean muscle and cut down on body fat. HMB has been shown to be effective at increasing lean muscle while decreasing muscle deterioration. Other benefits include lowered body fat and cholesterol and enhanced muscle repair after exercise.