HMB (beta-hydroxy-beta-methylbutyrate) is a bioactive nutrient belonging to the group of branched short-chain fatty acids, considered by some sources as a vitamin-like factor (similar to vitamins in terms of its effects), found naturally – in small quantities – in food, as well as produced by the human body as a result of the conversion of the branched-chain amino acid – leucine. Numerous studies show that adding HMB to the diet can facilitate the development of lean body mass due to its positive influence on the storing of muscle proteins and the reduction of fat tissue.