Leucine

About Leucine

Leucine is one of the three branched chain amino acids, together with isoleucine and valine, and is an essential amino acid that must be obtained from the diet. Beyond serving as a building block of proteins, leucine acts as a signaling molecule: it activates the mTORC1 pathway, a key regulator that switches on muscle protein synthesis, which is why it has received particular attention in sports and aging research. Dairy proteins such as whey are especially rich in leucine, and it is also abundant in meat, fish, eggs and soybeans. Leucine is strictly ketogenic, meaning its breakdown yields acetyl CoA and acetoacetate rather than glucose precursors, and a small fraction is converted to the metabolite HMB. Maple syrup urine disease is a rare inherited disorder in which the breakdown of branched chain amino acids is blocked, leading to their toxic accumulation and a characteristic sweet odor of urine. It is detected by newborn screening in many countries.