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β-Hydroxy β-Methylbutyrate
Leucine metabolite that helps prevent muscle breakdown and supports recovery, especially during caloric restriction or intense training.
What the evidence says
HMB helped in about half (6/10) of the studies that measured an effect — promising, but not unanimous.
Most evidence is from high-quality meta-analyses and randomised trials published 2009–2026 with a typical study size of 279 participants.
Based on 33 studies · 14 meta-analyses · 11 RCTs · 7,984 total participants
Confidence
HighWhat the studies found
By outcome
See full supplement plans that include HMB.
HMB has an evidence score of 8/10 — strong evidence based on 33 indexed studies, including 17 meta-analyses. Leucine metabolite that helps prevent muscle breakdown and supports recovery, especially during caloric restriction or intense training.
The commonly studied dose of HMB is 3g daily. Research points to an estimated optimal dose around 3g, with a minimum effective dose near 3g. Individual response varies — start low and adjust.
The best time to take HMB is in split doses through the day. Taking it with food is preferred. HMB (beta-hydroxy beta-methylbutyrate) is a leucine metabolite that reduces muscle protein breakdown via the ubiquitin-proteasome pathway and supports mTOR signaling.
Last reviewed May 2026 · evidence from 38 studies · how we score
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
HMB is a metabolite of the amino acid leucine. Its primary benefit is reducing muscle protein breakdown rather than increasing protein synthesis. Most effective for preventing muscle loss during caloric deficits, in older adults, or during very intense training periods. Benefits are more modest in well-trained individuals eating adequate protein.
Slows muscle protein breakdown
Supports muscle cell membrane integrity
How HMB works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
3g daily
Take with food
| Form | Type |
|---|---|
| 💊HMB-Ca (calcium salt) capsules or powder | Recommended |
| 💊HMB-FA (free acid) — faster absorption | Alternative |
HMB-FA absorbs faster and may be better pre-workout. HMB-Ca is more affordable and works well for daily use.
Minimum: 2 weeks
Optimal: 4 weeks
Cycling: Not required
Note: HMB-FA (free acid form) can be taken pre-workout for acute effects. HMB-Ca (calcium salt) is more common and can be taken anytime.
Meta-analyses show small but significant effects on total body mass and fat-free mass. Effect sizes are consistently reported as 'small' (ES ~0.21-0.22). Multiple studies show no significant effects in older adults or sarcopenia patients. HMB-FA form may have superior bioavailability to HMB-Ca.
Preserves muscle during dieting or overtraining
Less soreness and faster strength recovery
Insufficient data; avoid supplementation
May be particularly beneficial for preserving muscle mass
Generally safe to combine with other supplements and medications
Tip: Take with food
HMB is generally well-tolerated and considered safe for most healthy adults at recommended doses. The most commonly reported side effects are GI discomfort. Use caution if any of these apply to you: Known allergy or hypersensitivity to HMB or related compounds.
Citrulline Malate
Likely helpsCombines citrulline for nitric oxide production with malic acid for ATP synthesis — reduces fatigue and enhances exercise endurance.
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