HMB (Beta-Hydroxy Beta-Methylbutyrate)
Also known as: Beta-Hydroxy Beta-Methylbutyrate, HMB-FA, HMB-Ca, Ca-HMB, HMB free acid, HMB calcium salt, leucine metabolite
Effective Dosage
3 g daily (based on available study data)
What the Science Says
HMB is a natural byproduct of the amino acid leucine, produced in small amounts when your body breaks down protein. In the provided human studies, HMB supplementation (3 g/day) was shown to influence cortisol responses during fasting, and an HMB-enriched nutritional supplement combined with pulmonary rehabilitation improved body composition, bone mineral density, muscle strength, and quality of life in patients with a chronic lung condition. The free acid form (HMB-FA) absorbs faster and reaches higher peak blood levels than the calcium salt form, though both are commercially available.
What It Doesn't Do
Not proven to build muscle in healthy, well-nourished adults based on the studies provided. No evidence from these papers that it boosts athletic performance or speeds recovery in fit individuals. The cortisol-lowering effect was modest and seen only in a tiny 11-person study during fasting — don't expect it to be a stress-buster. Animal and fish studies cannot be used to make claims about human muscle growth.
Evidence-Based Benefits
HMB may modestly improve some sarcopenia-related parameters (e.g., phase angle, mid-arm muscle circumference, chair stand performance) in specific clinical populations such as cirrhosis patients, though between-group differences vs. control were not significant (PMID: 41544700). In elderly sarcopenic patients, HMB improved skeletal muscle mass index and grip strength within-group, with additional benefits when combined with prebiotics (PMID: 41627702). A meta-analysis of 13 RCTs (n=561) found HMB supplementation combined with resistance training did NOT significantly improve fat mass, muscle mass, or muscle strength in adults aged 50+ (PMID: 41934514).
Weak EvidenceEffective at: 1.5-3 g/day (based on study doses; no strong consensus from provided papers)
Source: auto-research
Absorption & Bioavailability
Moderate to Good — The free acid form (HMB-FA) in capsules showed 76% higher peak plasma concentration and reached peak levels 3x faster than the calcium salt form. When mixed in water, differences were smaller but still favored HMB-FA.
Red Flags to Watch For
- Most human evidence comes from very small studies (11 people in the fasting trial, 30 patients in the lung disease trial) — results may not apply broadly
- The bronchiectasis study used HMB as part of a multi-ingredient nutritional supplement combined with exercise rehab, making it impossible to isolate HMB's specific contribution
- Two of the seven indexed papers are irrelevant to human HMB supplementation (one is about cyanobacteria, one is about fish vaccine immune response) — the evidence base is thinner than the paper count suggests
- Animal data (piglet study) is sometimes used in marketing to imply muscle-building benefits in humans — this is not valid evidence for adult supplementation claims
- 256 registered supplement products contain HMB, but commercial availability does not equal proven efficacy
Research Sources
- PubMed
- NIH DSLD
This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-04-06