β-Hydroxy-β-methylbutyrate (HMB)

cofactor · 1

• ←Protein

  HMB is a breakdown product of leucine; only about 5% of leucine ends up as HMB, and its effect leans toward reducing muscle breakdown. The signal that switches on muscle building (mTOR) comes mainly from leucine itself. They are different switches, so adding HMB when protein intake is already adequate adds little.

  GUIDE · highREVIEW · moderate

regulates · 1

• ←Sarcopenia

  HMB is a breakdown product of leucine, usually taken at 3 g a day. It mainly reduces muscle breakdown rather than driving muscle building, so it fits situations dominated by breakdown: in a small trial of 19 older adults on 10 days of bed rest, the group taking HMB lost almost no lean mass. For people who simply train, the extra benefit is small.

  RCT · moderateREVIEW · low

contrast · 1

• ≠Creatine

  Creatine supports muscle building and high-intensity effort; HMB, a breakdown product of leucine, is thought to reduce muscle breakdown. The evidence for HMB is somewhat stronger in older adults losing muscle to acute illness, bed rest or chronic disease; in healthy young people its benefit is small. Whether taking the two together adds anything has been little studied.

  GUIDE · highREVIEW · highGUIDE · highREVIEW · high