RESEARCH MONOGRAPH · KDC-MN-399

HMB (β-Hydroxy-β-methylbutyrate)

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

73/100

Solid sarcopenia and bed-rest data; the trained-athlete claims are oversold relative to the elderly evidence

HMB is beta-hydroxy-beta-methylbutyrate, a downstream metabolite of leucine via ketoisocaproate. About 5 percent of dietary leucine ends up as HMB through the KIC dioxygenase pathway. The supplemental rationale is that direct HMB bypasses the rate-limiting step and provides higher tissue HMB exposure than equivalent leucine alone.

The clinical evidence splits sharply by population. In elderly, sarcopenic, and bed-rest populations, the HMB data is genuinely good. The Deutz, Wilson, and Cruz-Jentoft groups have demonstrated muscle protein synthesis support, attenuation of disuse atrophy, and clinically meaningful preservation of lean mass during bed rest at 3 g/day. The NUTRIVOLUNT trial and similar work in hospitalized elderly populations support the use case. So as an anti-catabolic supplement in catabolic conditions, the evidence is solid.

In trained healthy athletes, the picture is much weaker. The Nissen original work in the 1990s showed dramatic effects in untrained men starting resistance training, and those results have never been cleanly replicated in trained populations. The Wilson resistance-training meta-analyses show small or null effects in well-trained subjects. So the headline athletic claims are weaker than the supplement marketing suggests, while the elderly and catabolic use cases are stronger than most people realize.

What we like is the bed-rest data specifically, which is one of the cleaner controlled disuse models in human physiology. HMB at 3 g/day attenuates the muscle protein synthesis decrement during 10-day bed rest. That's a real finding with translational implications for hospitalized populations.

What we don't like is how HMB-FA (the free acid form, marketed as supposedly superior bioavailability) gets sold versus calcium HMB. The PK differences are modest and the clinical outcomes have not consistently differentiated.

Sourcing is reasonable. Both calcium HMB and HMB-FA are available at high purity from analytical suppliers, HPLC analysis is straightforward, stability is good in solid form. The free acid form is sticky and hygroscopic, which is an annoying handling issue.

Staying power is moderate, mostly tied to the elderly sarcopenia space rather than performance applications.

Evidence: 70
Mechanism: 75
Reliability: 68
Safety: 88
Sourcing: 80
Value: 70
Signal: 65
Staying power: 65

Plain-language summary Intrigue 48 / 100

HMB (beta-hydroxy-beta-methylbutyrate) is a metabolite of the branched-chain amino acid leucine, produced by about 5 percent of leucine breakdown. It reduces muscle protein breakdown by inhibiting the ubiquitin-proteasome pathway and stabilizing cell membranes, with secondary muscle-building effects through mTOR activation. The clinical evidence is strongest in catabolic states: HIV wasting, cancer cachexia, age-related sarcopenia, prolonged bed rest, post-surgical recovery, where reported research amounts reduce protein loss and preserve lean mass. In healthy resistance-trained athletes the effect is small and inconsistent, despite enthusiastic marketing. The free acid form (HMB-FA) has better pharmacokinetics than the calcium salt, but most published research uses Ca-HMB. Reference anti-catabolic supplement. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Leucine metabolite (anti-catabolic supplement)

Beta-hydroxy-beta-methylbutyrate; a leucine metabolite that reduces muscle protein breakdown; used in catabolic states and as a supplement.

Abstract

HMB (beta-hydroxy-beta-methylbutyric acid; CAS 625-08-1; molecular formula C5H10O3; molecular weight 118.13; Ca-HMB salt CAS 135236-72-5) is a metabolite of the branched-chain amino acid leucine, produced by approximately 5 percent of leucine catabolism via alpha-ketoisocaproate. Mechanism: HMB reduces muscle protein breakdown via inhibition of the ubiquitin-proteasome pathway and enhanced cell membrane integrity; secondary effects on muscle protein synthesis through mTOR pathway activation. The clinical evidence is strongest in catabolic states (HIV wasting, cancer cachexia, sarcopenia of aging, bedrest, post-surgical recovery) where reported research amounts reduce protein breakdown and preserve lean mass. In healthy resistance-trained athletes, the effect is small. The free acid form (HMB-FA) has improved pharmacokinetics over the calcium salt (Ca-HMB) but most research uses Ca-HMB. Plasma half-life is approximately 2 hours. Used as a reference anti-catabolic supplement.

Mechanism of action

Leucine metabolite; reduces muscle protein breakdown via ubiquitin-proteasome inhibition and enhanced membrane integrity. Secondary mTOR effects.

Reported research dose ranges

Reported research dose ranges vary across the published literature.

References

Wilson JM, et al. International Society of Sports Nutrition position stand: beta-hydroxy-beta-methylbutyrate (HMB). J Int Soc Sports Nutr 2013.
Deutz NE, et al. Effect of beta-hydroxy-beta-methylbutyrate (HMB) on lean body mass during 10 days of bed rest in older adults. Clin Nutr 2013.
Nissen S, et al. Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training. J Appl Physiol 1996.

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KDC-MN-399

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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HMB (β-Hydroxy-β-methylbutyrate)

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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