Switch Nutrition HMBHMB, or beta hydroxy beta methylbutyrate, is a metabolite of Leucine, one of the three branched chain amino acids (BCAAs). Leucine is considered the king of the amino acids because it has such a profound impact on MPS (muscle protein synthesis). HMB is 20x stronger than Leucine as it takes 20g of Leucine to produce just 1g of potent HMB. During intense physical activity or muscle stress, Leucine undergoes conversion into HMB, contributing to its