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HMB (β-hydroxy β-methylbutyrate)

A leucine metabolite marketed to spare muscle — real but modest, and clearest when you're new to training or in a catabolic state.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsAmino acidsMuscleRecovery

HMB is a small metabolite of leucine thought to reduce muscle breakdown. The evidence is genuine but more modest than the marketing suggests.

Key takeaways

  • HMB is a metabolite of leucine that appears to reduce muscle-protein breakdown and aid recovery.1
  • Benefits are clearest in untrained people, older adults, and catabolic states (illness, hard dieting).
  • In trained lifters eating enough protein, effects on muscle and strength are small and inconsistent.
  • Common dose is ~3 g/day, most effective started a couple of weeks before a hard training block.

What it is

Only a small fraction of dietary leucine is converted to HMB, so supplements provide much more than food. Its main proposed action is anti-catabolic — preserving muscle rather than adding it.

The evidence

The ISSN position stand concludes HMB can attenuate exercise-induced muscle damage and support recovery, and is most effective when taken for around two weeks before a hard bout.1 Gains in trained athletes with good protein intake are small.

Dose & how to use

3 g/day, split into doses (the free-acid form is absorbed faster). Best begun ahead of an intensified training phase.

Safety & who benefits

Well tolerated. Most worthwhile for beginners, older adults preserving muscle, and periods of heavy training or calorie restriction.

Bottom line: a modest muscle-preserver — genuinely useful in beginners, older adults and catabolic phases, marginal for well-fed trained lifters.

References

Adult research summary for education, not a prescription. These are food supplements, not treatments for disease.

  1. Wilson JM, et al. ISSN Position Stand: beta-hydroxy-beta-methylbutyrate (HMB). J Int Soc Sports Nutr 2013. pmc.ncbi.nlm.nih.gov

This article summarises nutrition and exercise science for education. It is not a substitute for individual medical advice; consult a professional before starting a supplement, in pregnancy, or alongside medication.