HMB (beta-hydroxy-beta-methylbutyrate)
Summary
In young adults doing resistance training, pooled trials found no meaningful gains in strength or lean mass from HMB, and effects in trained athletes were trivial. In adults over 50, HMB modestly improved muscle mass, grip strength and walking speed. Studies used 1.5–6 g/day, most often 3 g; short-term intake of 3 g/day appears safe in adults.
Key facts
- Calcium HMB monohydrate (HMB-Ca, about 13% calcium) and calcium-free HMB free acid (HMB-FA)[1]
- Free acid gel reached peak plasma levels faster (about 38 vs 128 minutes) and higher than calcium HMB in a small crossover PK study (D); outcome comparisons are lacking[6][1]
- Young adults in resistance training: no gain in fat-free mass or strength (no-effect); trained athletes: no effect (C); adults over 50: muscle mass, grip strength and gait speed ↑ (B)[2][3][4][9]
- 1.5–6 g/day, most commonly 3 g/day (3 g gave results equivalent to 6 g and better than 1.5 g)[1]
- Not on the AND/DoC/ACSM list of evidence-based ergogenic aids; the Australian Institute of Sport does not recommend it outside research; the ISSN says it can aid recovery from muscle-damaging exercise[1]
- 5 graded human outcomes on this page
- October 8, 2026
How it works
ProposedHMB is converted in the liver to HMG-CoA, a precursor for cholesterol synthesis; some experts hypothesize that exercise-damaged muscle cells need this for membrane repair (proposed). Experts also believe the conversion of leucine to HMB activates muscle protein synthesis and reduces protein breakdown (proposed). Getting 3 g/day from food would take more than 600 g/day of high-quality protein.[1]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Healthy aging | Grade B | Improved | Meta-analysis · n = 1,935 · 2025 | 1 row |
| Performance | Grade C | Mixed | Meta-analysis · n = 394 · 2009 | 4 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Muscle mass, strength and physical function in adults over 50 | Improved | Grade B | Meta-analysis · n = 1,935 · 2025 Adults over 50 in 21 randomized controlled trials Form: HMB (oral) · Dose: Subgroups at 3 g/day showed significant improvement · Duration: Subgroups lasting more than 12 weeks showed significant improvement HMB increased appendicular skeletal muscle mass (1.56 kg) and lean mass (0.28 kg), handgrip strength (0.54 kg), chair-stand time (-0.73 s) and gait speed (0.06 m/s). | 40248035 (opens PubMed)Source [4] |
| Strength in untrained vs trained young men | Mixed | Grade C | Meta-analysis · n = 394 · 2009 Trained and untrained young men in 9 resistance-training studies (mean age 23) Form: HMB · Dose: Varied across studies · Duration: About 5 weeks on average HMB gave small but clear gains in overall and leg strength in previously untrained men, but trivial strength effects in trained lifters. Effects on fat and fat-free mass were trivial. | 19387395 (opens PubMed)Source [5] |
| Strength and body composition in trained and competitive athletes | No effect | Grade C | Meta-analysis · n = 193 · 2018 Trained and competitive athletes in 6 randomized controlled trials Form: HMB · Dose: Varied; subgroups by dose showed no effect · Duration: Varied; subgroups by duration showed no effect Effects on bench press, leg press, body mass, fat-free mass and fat mass were trivial and not significant, with no heterogeneity between trials. | 29249685 (opens PubMed)Source [3] |
| Blood levels: free acid gel vs calcium HMB | Improved | Grade D | PK study · n = 16 · 2011 Healthy men and women in two crossover studies (4 men and 4 women each) Form: HMB free acid gel (swallowed or sublingual) vs calcium HMB capsule · Dose: 1 g calcium HMB or equivalent free acid · Duration: Single doses; blood sampled 3 h and 24 h Free acid gel peaked in plasma at about 38 minutes versus 128 minutes for calcium HMB, with higher peak levels (+185%) and nearly double the area under the curve; more HMB was retained. | 21134325 (opens PubMed)Source [6] |
| Fat-free mass and strength gains in young adults doing resistance training | No effect | No effect | Meta-analysis · n = 302 · 2020 Young adults aged 18-45 in 11 resistance-training studies (302 in body composition analyses, 248 in strength analyses) Form: HMB (form not broken down in the abstract) · Dose: Varied across studies · Duration: Periods of resistance training HMB produced a small gain in total body mass but no significant effect on fat-free mass, fat mass or one-rep-max strength. | 32456217 (opens PubMed)Source [2] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Calcium HMB monohydrate (HMB-Ca) | Varies[1] | Slower and lower plasma peak than free acid gel in a small crossover study.[6] | 3 g/day for 3–8 weeks was well tolerated in nine studies, with no adverse effects on blood chemistry or hematology.[7][1] | Most trials |
| HMB free acid (HMB-FA) | Varies[1] | Faster and greater rise in plasma HMB than the calcium salt; outcome comparisons are lacking (ODS).[6][1] | No form-specific tolerance data in our sources.[1] | Fewer trials; an option for people limiting calcium (ODS) |
Studied doses
Doses studied in human trials ranged from 1.5 to 6 g of HMB a day, most often 3 g. Exercise studies supplemented for 1 day to 6 weeks within training programs of up to 12 weeks; some trials in adults over 50 lasted longer than 12 weeks.[1][4]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- Teens
- HMB's safety and efficacy have not been studied in adolescents (ODS).[1]
- Long-term use
- Short-term use of 3 g/day appears safe in adults, but there is no expert consensus on taking HMB for several months or longer.[1][7]
- Calcium intake
- Calcium HMB at 3 g/day adds about 400 mg of calcium; the free acid form is calcium-free.[1]
- Before you start
- Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Articles about HMB (beta-hydroxy-beta-methylbutyrate)
Plain-English answers to common questions, built on the evidence above.
Frequently asked questions
Does HMB build muscle?
In young adults doing resistance training, a 2020 meta-analysis found no significant effect on fat-free mass or strength, and a 2018 meta-analysis in trained athletes found trivial effects. Small strength gains were seen in previously untrained men in an older analysis.[2][3][5]
Does HMB help older adults?
A 2025 meta-analysis of 21 trials in adults over 50 found small gains in muscle mass, grip strength, chair-stand time and walking speed, mainly at 3 g/day for more than 12 weeks.[4]
Calcium HMB or free acid?
Free acid gel raises blood HMB faster and higher than calcium HMB, but ODS notes more studies are needed to compare the forms' effects. Calcium HMB at 3 g/day adds about 400 mg calcium.[6][1]
Sources
- [1]Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024. fact-sheet
- [2]Supplementation with the Leucine Metabolite β-hydroxy-β-methylbutyrate (HMB) does not Improve Resistance Exercise-Induced Changes in Body Composition or Strength in Young Subjects: A Systematic Review and Meta-Analysis.. Nutrients, 2020. meta-analysis
- [3]Effects of beta-hydroxy-beta-methylbutyrate supplementation on strength and body composition in trained and competitive athletes: A meta-analysis of randomized controlled trials.. J Sci Med Sport, 2018. meta-analysis
- [4]Effects of oral supplementation of β -hydroxy-β -methylbutyrate on muscle mass and strength in individuals over the age of 50: a meta-analysis.. Front Nutr, 2025. meta-analysis
- [5]Effects of beta-hydroxy-beta-methylbutyrate supplementation during resistance training on strength, body composition, and muscle damage in trained and untrained young men: a meta-analysis.. J Strength Cond Res, 2009. meta-analysis
- [6]Free acid gel form of β-hydroxy-β-methylbutyrate (HMB) improves HMB clearance from plasma in human subjects compared with the calcium HMB salt.. Br J Nutr, 2011. PK-study
- [7]beta-hydroxy-beta-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factors.. J Nutr, 2000. review
- [8]Beta-hydroxy-beta-methylbutyrate ingestion, part II: effects on hematology, hepatic and renal function.. Med Sci Sports Exerc, 2000. RCT
- [9]Ergogenic Benefits of β-Hydroxy-β-Methyl Butyrate (HMB) Supplementation on Body Composition and Muscle Strength: An Umbrella Review of Meta-Analyses.. J Cachexia Sarcopenia Muscle, 2025. meta-analysis
What changed
- First draft. Every evidence-row PMID checked with NCBI E-utilities (esummary + efetch abstract) and re-read in an independent adversarial pass.