HMB Dosage Calculator
A leucine metabolite that inhibits muscle protein breakdown (proteolysis) rather than stimulating synthesis. Most effective for untrained beginners, older adults, and athletes in caloric deficits where catabolism is the primary problem.
What is HMB?
β-Hydroxy β-methylbutyrate (HMB) is a bioactive metabolite of the essential amino acid leucine, produced in small quantities (~0.3 g/day) via the BCAA transamination pathway. While leucine activates mTORC1 to stimulate muscle protein synthesis, HMB operates via a distinct mechanism: it inhibits the ubiquitin-proteasome pathway (the primary route of exercise-induced muscle protein breakdown) and activates the PI3K/Akt cell survival pathway, reducing myofibrillar damage and apoptosis. It also modestly activates mTOR independently. This anti-catabolic profile distinguishes HMB from most protein/amino acid supplements and explains its specific utility in contexts where muscle breakdown is the dominant problem: caloric restriction, sarcopenia (age-related muscle loss), extreme training volumes, and deconditioned individuals beginning resistance programs. Meta-analyses confirm HMB's greatest benefits in untrained individuals (lean mass gains of ~0.5–1 kg over 4 weeks) and in older adults, while effects in well-trained athletes at maintenance calories are smaller.
How to Take HMB
**Standard dose:** 3 g/day (approximately 0.04 g/kg for a 75 kg adult), divided into three 1 g doses with meals. Two forms: HMB calcium salt (HMB-Ca) requires 60–90 minutes to peak plasma; HMB free acid (HMB-FA) peaks within 30 minutes and achieves significantly higher plasma concentrations. **Pre-workout (HMB-FA):** 1–3 g of HMB-FA taken 30 minutes before training reduces acute exercise-induced muscle damage markers (CK, LDH) more effectively than HMB-Ca. **During caloric deficit:** 3 g/day HMB-Ca is the evidence-supported dose for lean mass preservation during weight loss.
Timing Recommendations
HMB-Ca: three divided doses with meals throughout the day (morning, midday, evening). HMB-FA: 30 minutes pre-workout for acute muscle protection, plus 1 g with a post-workout meal. On rest days, take three equal doses with meals regardless. Unlike creatine, HMB has no loading phase — steady-state plasma levels are achieved within the first week of daily dosing.
Potential Side Effects & Safety
HMB is extremely well tolerated. No serious adverse effects have been reported in any clinical trial at 3 g/day. Mild GI discomfort may occur at the start in a minority of users. HMB does not cause the virilising effects of anabolic steroids despite similar claims in early marketing; it is not a hormonal compound. No significant drug interactions have been identified.
Who should avoid HMB?
No absolute contraindications. The primary caution is managing expectations: HMB's effects in trained athletes at maintenance calories are modest, and the supplement cost-to-benefit ratio may be unfavourable compared to optimising total protein intake. Most beneficial for: beginners, elderly sarcopenic individuals, athletes cutting weight, and those recovering from injury.
Best Stacks with HMB
HMB + creatine synergistically covers both muscle catabolism (HMB) and phosphocreatine replenishment (creatine) — a meta-analysis found the combination superior to either alone for lean mass and strength. HMB + leucine-rich whey protein post-workout stacks both anti-catabolic (HMB) and anabolic (leucine/mTOR) pathways. During caloric restriction: HMB + vitamin D3 addresses two independently validated lean mass preservation strategies.
Scientific References
All dosage recommendations are grounded in peer-reviewed research.
- 1International Society of Sports Nutrition Position Statement: beta-hydroxy-beta-methylbutyrate (HMB)
Journal of the International Society of Sports Nutrition · 2014
- 2A meta-analysis of the effects of HMB on muscle mass, strength, and power
Journal of Strength and Conditioning Research · 2012
HMB Dosage Calculator
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Safety notes
- HMB-FA peaks in 30 min vs 90 min for HMB-Ca — choose HMB-FA for acute pre-workout muscle protection.
- Greatest benefit in beginners, older adults, and athletes in caloric deficit — not a standalone muscle-builder.
- Three divided doses throughout the day are more effective than a single large dose.
- HMB is not a hormonal compound despite aggressive marketing claims — it works via anti-catabolic pathways.
This calculator provides general guidance only. Always consult a qualified healthcare professional before starting any supplement.