HMB

Also known as beta-hydroxy beta-methylbutyrate, hydroxymethylbutyrate.

Last reviewed October 9, 2026 · Jump to references

What is HMB?

In plain words

HMB is a substance the body makes from leucine, a building block of protein. It may help muscle cells make protein and slow its breakdown. Researchers study it for age-related muscle loss, muscle loss during illness, and recovery from exercise. Human studies have mixed results, so it has not been shown to reliably preserve muscle in everyone.

Technical definition

HMB (β-hydroxy-β-methylbutyrate) is a five-carbon hydroxy acid produced during metabolism of the essential amino acid leucine. It has no established dedicated receptor; experimental evidence links it to mTORC1-associated protein synthesis and reduced protein breakdown through pathways including the ubiquitin–proteasome system. HMB is marketed in the United States as a dietary supplement, not an FDA-approved treatment for muscle loss.

Educational information only. This page does not provide medical advice or determine whether a supplement is appropriate for you. Review supplements with a qualified healthcare professional, especially if you take medication, are pregnant, have surgery scheduled, or have a chronic medical condition.

Evidence by use

Each use is rated on its own. There is no single overall effectiveness score.