Evidence-based·Last reviewed May 31, 2026·How we grade evidence

Calcium hydroxymethylbutyrate

Amino-acidLeucine metaboliteBest with a meal

Calcium HMB is the dominant commercial form of β-hydroxy-β-methylbutyrate, a leucine metabolite that modestly suppresses muscle-protein breakdown. The strongest evidence is for preserving lean mass in catabolic states — elderly sarcopenia, bed rest, and clinical wasting — and the ISSN position stand supports 3 g/day for recovery and muscle damage attenuation. Effects in already-trained athletes are small.

Quick decision guide

May help most

Older adults at risk of sarcopenia (especially those with reduced protein intake or limited mobility); patients facing bed rest, surgery recovery, or clinical wasting; untrained adults starting resistance training.

Common dosing range

3 g/day (≈38 mg/kg), divided 2–3× daily; 1 g 30–60 minutes before exercise on training days.

When to expect effects

2 weeks to attenuate muscle damage; 4–12 weeks for lean-mass changes.

Watch out for

Few side effects at the standard 3 g/day dose. Provides ~440 mg elemental calcium per 3 g Ca-HMB — count toward your daily calcium total if you also take a calcium supplement.

Evidence snapshot

Lean-mass preservation in bed rest / sarcopeniaModerate

Recovery from intense exerciseModerate

Strength gains in untrained adultsEmerging

Strength gains in resistance-trained athletesLow (small effect)

What is it

Calcium beta-hydroxy-beta-methylbutyrate (calcium HMB) is the calcium salt of HMB, a metabolite of the essential branched-chain amino acid leucine. It is used as a supplement for muscle preservation, particularly in older adults, athletes, and clinical conditions involving muscle loss.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

You're an older adult (65+) at risk of sarcopenia and your protein intake is hard to optimise

You're facing planned bed rest (post-op recovery, immobilisation, hospitalisation) and want to limit muscle loss

You're a previously untrained adult starting a resistance-training programme and want to support early adaptation

You do high-volume eccentric or unaccustomed training and want to attenuate next-day soreness and damage markers

You have a clinical wasting condition (COPD, HIV, cancer cachexia) and your clinician suggests adjunct HMB

Probably skip if…

You're an experienced lifter or athlete with sustained training and a creatine + adequate protein routine already in place — added strength and hypertrophy benefit is small

Your daily protein is already at ~1.6 g/kg and you're consistently eating leucine-rich meals — endogenous HMB production from leucine is likely sufficient

You're hoping for fat loss — HMB has minimal effect on fat mass

You can't or won't take 3 doses per day — single bolus dosing of Ca-HMB is less effective than divided dosing

You're on a strict low-calcium diet for medical reasons (then use HMB-FA, which contains no calcium)

Evidence at a glance

Goal	Effect	Best fit	Time
Lean-mass preservation in bed rest / immobilisation Good Evidence	Prevented ~2 kg lean-mass loss vs placebo over 10 days of bed rest	Older adults (60+) facing planned or actual bed rest, immobilisation, or hospitalisation	Days — measurable preservation within the 10-day bed-rest window
Sarcopenia / lean-mass preservation in older adults Good Evidence	+0.35 kg lean body mass vs placebo at ≥4 weeks in adults ≥65 years	Adults ≥65 with documented or at-risk sarcopenia; clinical-wasting populations under medical care	4–12 weeks
Exercise-induced muscle damage attenuation Good Evidence	Significant reduction in CK and LDH rises after intense exercise; modest reduction in subjective soreness	Adults doing high-volume eccentric training, unaccustomed exercise, or competitive training blocks	2 weeks of consistent dosing before the muscle-damage-attenuation effect is consistent
Strength and hypertrophy gains in untrained adults starting resistance training Limited Evidence	Small: +1–2% strength, +0.3% lean mass over training-only controls; larger in untrained vs trained	Previously untrained adults beginning a structured resistance-training programme	8–12 weeks of consistent training + HMB dosing
Clinical muscle wasting (cachexia, COPD, HIV, cancer) Limited Evidence	Modest lean-mass preservation; inconsistent functional outcomes	Adults with COPD, HIV, cancer cachexia, or post-ICU under physician care, combined with rehabilitation	4–12 weeks

Lean-mass preservation in bed rest / immobilisation

Good Evidence

Effect: Prevented ~2 kg lean-mass loss vs placebo over 10 days of bed rest
Best fit: Older adults (60+) facing planned or actual bed rest, immobilisation, or hospitalisation
Time: Days — measurable preservation within the 10-day bed-rest window

Sarcopenia / lean-mass preservation in older adults

Good Evidence

Effect: +0.35 kg lean body mass vs placebo at ≥4 weeks in adults ≥65 years
Best fit: Adults ≥65 with documented or at-risk sarcopenia; clinical-wasting populations under medical care
Time: 4–12 weeks

Exercise-induced muscle damage attenuation

Good Evidence

Effect: Significant reduction in CK and LDH rises after intense exercise; modest reduction in subjective soreness
Best fit: Adults doing high-volume eccentric training, unaccustomed exercise, or competitive training blocks
Time: 2 weeks of consistent dosing before the muscle-damage-attenuation effect is consistent

Strength and hypertrophy gains in untrained adults starting resistance training

Limited Evidence

Effect: Small: +1–2% strength, +0.3% lean mass over training-only controls; larger in untrained vs trained
Best fit: Previously untrained adults beginning a structured resistance-training programme
Time: 8–12 weeks of consistent training + HMB dosing

Clinical muscle wasting (cachexia, COPD, HIV, cancer)

Limited Evidence

Effect: Modest lean-mass preservation; inconsistent functional outcomes
Best fit: Adults with COPD, HIV, cancer cachexia, or post-ICU under physician care, combined with rehabilitation
Time: 4–12 weeks

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Lean-mass preservation in bed rest / immobilisation

Supplement benefit

Good Evidence

The clearest single-trial result for HMB. In 24 older adults (60–76 years) undergoing 10 days of strict bed rest, Ca-HMB 3 g/day completely prevented the lean-mass loss seen in the placebo group (placebo lost ~2.05 kg lean mass; HMB maintained mass). The proposed mechanism is attenuation of ubiquitin-proteasome–mediated protein breakdown plus modest mTOR stimulation. Highly relevant for older patients facing planned surgery, hospitalisation, or immobilisation periods.

Effect size

Prevented ~2 kg lean-mass loss vs placebo over 10 days of bed rest

Time to effect

Days — measurable preservation within the 10-day bed-rest window

Best fit

Older adults (60+) facing planned or actual bed rest, immobilisation, or hospitalisation

Less likely

Healthy active younger adults not facing immobilisation

Bottom line: The single most-cited HMB result. Reasonable to start 1 week before planned bed rest and continue through the immobilisation period.

SourceDeutz et al., 2013 — Clinical Nutrition

Sarcopenia / lean-mass preservation in older adults

Supplement benefit

Good Evidence

A 2015 meta-analysis of 7 RCTs in adults aged 65+ found HMB (mostly 3 g/day for ≥4 weeks) preserved lean body mass by ~0.35 kg versus placebo with no significant effect on fat mass or strength scores. Effect was strongest in participants with sarcopenia or who were largely sedentary. A 2019 systematic review in clinical adult populations (COPD, HIV, cancer cachexia) confirmed a consistent signal for lean-mass preservation, particularly when combined with resistance exercise or rehabilitation programmes.

Effect size

+0.35 kg lean body mass vs placebo at ≥4 weeks in adults ≥65 years

Time to effect

4–12 weeks

Best fit

Adults ≥65 with documented or at-risk sarcopenia; clinical-wasting populations under medical care

Less likely

Robust older adults with adequate protein intake (≥1.2 g/kg/day) and regular resistance training — endogenous HMB likely sufficient

Bottom line: Real, modest benefit for muscle preservation in older adults — best paired with resistance exercise and adequate protein.

SourceWu et al., 2015 — Archives of Gerontology and Geriatrics Bear et al., 2019 — American Journal of Clinical Nutrition

Exercise-induced muscle damage attenuation

Supplement benefit

Good Evidence

The ISSN position stand summarises that HMB 3 g/day reduces markers of exercise-induced muscle damage (CK, LDH) and perceived muscle soreness after intense or unaccustomed training. Effect is more apparent with high-volume eccentric work or in those new to a training stimulus. The newer HMB free acid (HMB-FA) form reaches peak plasma concentration faster (~30 min vs ~120 min for Ca-HMB) with ~7× higher Cmax, and is positioned for pre-workout dosing.

Effect size

Significant reduction in CK and LDH rises after intense exercise; modest reduction in subjective soreness

Time to effect

2 weeks of consistent dosing before the muscle-damage-attenuation effect is consistent

Best fit

Adults doing high-volume eccentric training, unaccustomed exercise, or competitive training blocks

Less likely

Light-to-moderate exercisers with no soreness concerns

Bottom line: Sensible adjunct during high-volume or pre-competition training blocks; less compelling for casual training.

SourceWilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition Bear et al., 2019 — American Journal of Clinical Nutrition

Strength and hypertrophy gains in untrained adults starting resistance training

Supplement benefit

Limited Evidence

Meta-analysis of HMB in resistance-trained adults found small effect sizes — bench press ~+1.4%, leg press ~+1.7%, lean mass +0.28% — versus placebo. Effects were larger in untrained subjects starting a programme than in already-trained athletes. The ISSN position stand notes HMB is most useful at the beginning of a new training stimulus, when adaptation to the unaccustomed workload generates the most muscle protein breakdown for HMB to attenuate.

Effect size

Small: +1–2% strength, +0.3% lean mass over training-only controls; larger in untrained vs trained

Time to effect

8–12 weeks of consistent training + HMB dosing

Best fit

Previously untrained adults beginning a structured resistance-training programme

Less likely

Experienced lifters; competitive athletes whose adaptation gains are nearer ceiling

Bottom line: Useful in the first 8–12 weeks of starting a resistance programme; diminishing returns for experienced trainees.

Evidence is mixed

Effect magnitude in trained athletes is smaller than early HMB literature suggested. Magnitude is real but modest; expectations should reflect that.

SourceRowlands & Thomson, 2009 — Journal of Strength and Conditioning Research· conflicting

SourceRowlands & Thomson, 2009 — Journal of Strength and Conditioning Research Wilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition

Clinical muscle wasting (cachexia, COPD, HIV, cancer)

Disease adjunct

Limited Evidence

Systematic reviews of HMB in clinical adult populations (often as part of a HMB + arginine + glutamine cocktail) show consistent signals for lean-mass preservation, particularly when combined with rehabilitation programmes. Effects on mortality and functional strength are inconsistent. Generally used as an adjunct under physician supervision, not as primary therapy. Trials are smaller and more heterogeneous than in the sarcopenia and bed-rest literature.

Effect size

Modest lean-mass preservation; inconsistent functional outcomes

Time to effect

4–12 weeks

Best fit

Adults with COPD, HIV, cancer cachexia, or post-ICU under physician care, combined with rehabilitation

Less likely

Adults with advanced terminal cachexia — survival benefit not established

Bottom line: Reasonable adjunct under medical supervision in clinical wasting; don't expect dramatic effects on its own.

SourceBear et al., 2019 — American Journal of Clinical Nutrition

How it works

HMB is produced naturally in the body from leucine, with approximately 5% of dietary leucine being converted to HMB. HMB has anti-catabolic effects, reducing muscle protein breakdown through inhibition of the ubiquitin-proteasome pathway and reducing markers of muscle damage. It also has modest anabolic effects, supporting protein synthesis via mTOR pathway activation. Research suggests HMB is particularly effective at preserving lean muscle mass during periods of catabolic stress, including bed rest, illness, aging-related sarcopenia, and intense exercise training. It may reduce post-exercise muscle damage and accelerate recovery. The effects are most pronounced in untrained individuals, older adults, and clinical populations with muscle wasting. The ergogenic effects of HMB in trained athletes are debated, with some studies showing benefit and others showing no effect. In clinical nutrition, HMB has been incorporated into specialized formulas for cancer cachexia, COPD, AIDS-related wasting, and recovery from major illness. The calcium component contributes to total calcium intake.

How to take it

1. Typical dose

• 3 g/day total (≈38 mg/kg body mass) — the standard ISSN-supported dose • Split into 3 × 1 g doses across the day, OR 2 × 1.5 g • On training days: take one 1 g dose 30–60 min before exercise (longer lead with Ca-HMB, shorter with HMB-FA) • Bed-rest / surgery prep: start 5–7 days before planned bed rest at 3 g/day; continue through the immobilisation period

2. Higher studied dose

Doses up to 6 g/day have been used short-term in clinical wasting trials with no notable safety concerns; no clear added benefit over 3 g/day in most contexts. Doses below 1.5 g/day are likely too low for the lean-mass effect.

3. Timing

Divide across the day for steady plasma levels. Pre-exercise dose (1 g, 30–60 min before training) capitalises on attenuated muscle damage. With Ca-HMB, allow at least 60 minutes for peak; HMB-FA peaks within 30 minutes.

4. With food

With or without food. Taking with a protein-containing meal pairs well with the leucine pathway HMB acts on.

5. Split dosing

Yes — 3 × 1 g per day across the day is the standard protocol. Single bolus dosing is less effective for sustained lean-mass effects.

6. How long to try

4 weeks minimum to see lean-mass effects; 8–12 weeks for resistance-training adaptation. ISSN supports up to a year of continuous 3 g/day use in healthy adults; longer-term safety data is limited but the 1-year safety record is reassuring.

What to track

Body composition (DEXA or BIA) at baseline and 12 weeks for lean-mass response

Strength benchmarks (1RM or rep-out estimates) for resistance-training adaptation

Soreness / DOMS ratings around hard training blocks

Total daily protein intake — HMB doesn't replace adequate protein (~1.6 g/kg if training)

Total daily calcium intake — Ca-HMB contributes ~440 mg elemental Ca per 3 g; count toward your target

Bottom line: 3 g/day divided 3×, ideally with one dose pre-training. Pair with adequate protein (~1.6 g/kg) and progressive resistance training for the best response.

3 commercial forms

Compare the main delivery options and what they’re best suited for.

Calcium HMB (Ca-HMB monohydrate)

Most studied

Calcium salt of β-hydroxy-β-methylbutyrate; the form used in the vast majority of HMB clinical trials including ISSN's underlying evidence base. ~13% elemental calcium by weight (3 g Ca-HMB provides ~440 mg Ca). Bench durability, cheap, capsules and powders widely available. Peak plasma at ~120 minutes after oral dose.

Standard clinical-trial form; slower peak than HMB-FA.

HMB Free Acid (HMB-FA)

Faster kinetics

Newer free-acid form. Reaches peak plasma at ~30 minutes with ~7× higher Cmax and ~25% greater AUC than Ca-HMB. Positioned for pre-workout dosing where rapid plasma rise matters. Contains no calcium — preferable for people on calcium-restricted diets. Costlier and less widely tested in long-term clinical settings.

Faster, higher peak; useful pre-exercise; clinical-trial evidence base is smaller than Ca-HMB.

HMB in clinical wasting cocktails (HMB + arginine + glutamine)

Medical product

HMB combined with arginine and glutamine (often as Juven by Abbott or similar). Used as an adjunct in cancer cachexia, HIV-related wasting, and wound healing trials. Reasonable evidence base for these specific indications under medical supervision; not the right form for general sports use.

Medical-foods category; targeted at clinical wasting, not training.

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

mild GI upset (uncommon)occasional bad taste with the powder form

Serious risks

No serious adverse effects have been documented with HMB at 3 g/day in healthy adults or in clinical populations across multi-month and 1-year trials. Liver, kidney, and lipid panels have been unchanged in studied populations.
SourceWilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition Bear et al., 2019 — American Journal of Clinical Nutrition
Ca-HMB delivers ~440 mg elemental calcium per 3 g — when stacked with calcium supplements, dairy intake, and fortified foods you can exceed the 2,000–2,500 mg/day UL. Excess long-term calcium intake has been linked to cardiovascular concerns.
SourceHoleček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle

Who should avoid it

People with hypercalcaemia, parathyroid disorders, or kidney stones triggered by calcium — use HMB free acid (HMB-FA) instead to avoid the calcium load.
SourceHoleček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle
Children and adolescents — HMB has not been adequately studied in under-18s; supplementing during growth is unnecessary in the context of adequate protein intake.
SourceWilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition
People with significant renal impairment — protein-metabolite handling is altered; discuss with your nephrologist.
SourceHoleček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle

Pregnancy & breastfeeding

HMB has not been studied in pregnancy or breastfeeding. There's no clear indication for supplemental HMB during pregnancy — adequate dietary protein is the priority. Avoid supplementation unless your obstetrician specifically recommends it.

SourceWilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition

Bottom line: Very well tolerated at the standard 3 g/day in adults. Main practical caveat is the calcium load if you use Ca-HMB and already take calcium supplements.

Interactions

calcium supplements and high-dose calcium-fortified productsMinor

Ca-HMB adds ~440 mg elemental calcium per 3 g dose. Combined with other calcium sources you can exceed the 2,000–2,500 mg/day UL. Switch to HMB-FA if calcium intake is a concern.

SourceHoleček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle

leucine and branched-chain amino acid supplementsMinor

HMB is a leucine metabolite. Combining doesn't appear to cause harm but the synergy beyond either alone is not well-established. Adequate dietary leucine (from protein) is the foundation either way.

SourceHoleček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle

creatine monohydrateMinor

Combining HMB + creatine in resistance trainees has shown small additive effects in some trials; no negative interactions reported.

SourceWilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition

tetracycline antibiotics (with Ca-HMB)Minor

Calcium in Ca-HMB can chelate tetracyclines and reduce absorption. Separate by 2 hours, or use HMB-FA, or pause HMB during the antibiotic course.

SourceHoleček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle

Food sources

Food	Amount	%DV
Catfish, cooked	3 oz / 85 g (~0.1 g HMB; via leucine conversion)	—
Grapefruit	1 medium / ~250 g (~0.04 g HMB)	—
Asparagus, cooked	1 cup / ~180 g (~0.03 g HMB)	—
Alfalfa sprouts	1 cup / ~30 g (~0.005 g HMB)	—
Leucine-rich protein foods (dairy, meat, fish)	Per 20–25 g protein, ~5% of leucine becomes HMB (~0.1–0.2 g)	—

Catfish, cooked

Amount: 3 oz / 85 g (~0.1 g HMB; via leucine conversion)
%DV: —

Grapefruit

Amount: 1 medium / ~250 g (~0.04 g HMB)
%DV: —

Asparagus, cooked

Amount: 1 cup / ~180 g (~0.03 g HMB)
%DV: —

Alfalfa sprouts

Amount: 1 cup / ~30 g (~0.005 g HMB)
%DV: —

Leucine-rich protein foods (dairy, meat, fish)

Amount: Per 20–25 g protein, ~5% of leucine becomes HMB (~0.1–0.2 g)
%DV: —

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

'Calcium HMB' or 'CaHMB' clearly stated; per-serving HMB dose listed in grams (1 g per serving × 3 servings/day is the standard)

Capsule or powder format both fine; powder lets you split a 1 g pre-workout dose more cleanly

Third-party tested (USP, NSF Certified for Sport, Informed-Sport) — important for competitive athletes

Single-ingredient product if you're evaluating effect — combo 'muscle-builder' formulas obscure dosing

Consider HMB free acid (HMB-FA) if you want faster pre-workout kinetics, can't tolerate the calcium load, or take long-term high-dose protocols

Be skeptical of…

Mega-dose promises ('10× faster muscle growth') — meta-analysis effects in trained athletes are 1–2%

Fat-loss claims — HMB has minimal effect on fat mass

Pre-workout combos that hide the HMB dose behind a 'proprietary blend' — you need to know you're getting at least 1 g per serving

HMB-based 'natural anabolic' products marketed at adolescents — no need and not studied in under-18s

Combination products that ALSO contain undeclared calcium beyond what's in the Ca-HMB itself — easy to over-shoot calcium UL

Frequently asked questions

What is HMB?⌄

HMB (beta-hydroxy beta-methylbutyrate) is a metabolite of the amino acid leucine. About 5% of dietary leucine is converted to HMB in the body. It has anti-catabolic and modest anabolic effects on muscle.

How much HMB should I take?⌄

Standard dose is 3 grams per day of calcium HMB, divided into three 1-gram doses with meals. Free acid HMB doses are slightly lower (2-2.5 grams).

Does HMB build muscle?⌄

HMB primarily preserves muscle (reduces breakdown) rather than dramatically building muscle. Effects on muscle gains are modest and most pronounced in untrained individuals or those starting resistance training.

Is HMB worth it for athletes?⌄

For well-trained athletes, the ergogenic effects are modest and inconsistent. For untrained individuals, older adults, and those recovering from injury or illness, HMB has more robust benefits.

Is HMB safe to take daily?⌄

Yes, clinical trials lasting up to a year have shown excellent safety with daily HMB supplementation at standard doses.

References by claim

Exercise-induced muscle damage attenuation

Wilson et al. (ISSN position stand), 2013 — PMC — Journal of the International Society of Sports Nutrition (2013) link

Safety

Holeček, 2017 — PMC — Journal of Cachexia, Sarcopenia and Muscle (2017) link

Sarcopenia / lean-mass preservation in older adults

Wu et al., 2015 — Archives of Gerontology and Geriatrics (2015) link

Bear et al., 2019 — American Journal of Clinical Nutrition (2019) link

Lean-mass preservation in bed rest / immobilisation

Deutz et al., 2013 — Clinical Nutrition (2013) link

Strength and hypertrophy gains in untrained adults starting resistance training

Rowlands & Thomson, 2009 — Journal of Strength and Conditioning Research (2009) link

Other references

Fuller et al., 2011 — British Journal of Nutrition (2011) link

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Evidence-based·Last reviewed May 31, 2026·Evidence current as of May 31, 2026·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.