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VITAMINS & SUPPLEMENTS · GUIDE

HMB (Beta-Hydroxy-Beta-Methylbutyrate): Muscle Preservation Evidence

HMB is a leucine by-product sold for muscle. See what reviews and the sports-nutrition position statement found for older adults, training and illness, and the limits.

Content last updated . This page has not been medically reviewed.

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Quick answer
HMB (beta-hydroxy-beta-methylbutyrate) has been studied for keeping or building muscle. Reviews find small average gains in muscle mass or strength in some groups, but many trials have a high risk of bias and results differ by population and whether exercise is also done. It is not a substitute for strength training, enough food, or medical care for muscle loss. Talk to a clinician or pharmacist before use if you are older, ill, pregnant, have kidney or liver disease, or take medicines.

What it is

HMB is a metabolite (a by-product) of the amino acid leucine that humans and other animals make naturally. [1] It is not itself a protein-building amino acid. Two supplement forms have been studied: a calcium form and a free-acid form. [1] For leucine itself, see BCAAs.

What the research found

6 findings · 1 supported · 3 mixed · 2 limited or unclearThe colour follows the evidence label on each card.

  1. People with illness or muscle-wasting conditions

    Small effect; biased trials

    A meta-analysis of 15 trials (2,137 patients) found HMB, or supplements containing HMB, increased muscle mass and strength, although the effect size was small. No study had low risk of bias in all categories. [2]

  2. Older adults, body composition

    Mixed

    A review of 9 studies (448 people) found more fat-free mass with HMB, but no added change when HMB was combined with exercise. [3]

  3. Older adults doing resistance training

    Limited

    A 2025 review of 10 trials (596 people) found modest gains in handgrip strength and a physical performance score, but no significant effects on gait speed, lean mass, fat mass or body weight; half the trials were at high risk of bias. [4]

  4. Adults generally (summary of reviews)

    Mixed quality

    An umbrella review of 11 meta-analyses found increased muscle mass, and rated study quality as high for five, low for three and critically low for three. [5]

  5. Trained athletes

    Mixed

    The position statement says performance benefits in trained athletes are mixed. [1]

  6. HMB compared with leucine

    One small trial, young men only

    One 12-week trial in 26 resistance-trained young men gave whey protein plus either HMB or leucine and found no differences in muscle or strength gains; its authors concluded HMB was no more effective than leucine. [6]

Many HMB studies test products that also contain other nutrients, so the effect of HMB alone can be hard to separate. [2]

What the sports-nutrition position statement says

The International Society of Sports Nutrition (ISSN) published a 2025 position stand with 12 points. It says safety data suggest chronic use of the two forms is safe in humans for up to at least one year. [1] It says HMB may be important in non-exercising, sedentary and aging people for muscle strength, function and quality. [1] The position stand points to research using a daily amount based on body weight, together with exercise. [1] That is a study amount, not a personal recommendation, and we do not give one here.

Be aware of context: several authors disclosed current or past ties to a company that marketed HMB forms. [1] A position stand is expert opinion based on studies, and reviews above show smaller or mixed effects.

Muscle loss with age: what matters more

Muscle loss has many causes and is best assessed by a clinician. See Sarcopenia and muscle loss, strength training and protein for older adults and Protein for older adults. Unplanned weight loss needs a medical review: unintentional weight loss.

Label tips

Check which form (calcium or free acid), the amount per serving, and any added ingredients in blends. Do not combine several products with overlapping ingredients without advice.

Frequently asked questions

What is HMB?

It is a by-product of the amino acid leucine made in the body and also sold as a supplement. [1]

Does HMB build muscle?

Reviews found small increases in muscle mass or strength in some groups, mixed results in older adults who also exercise, and many trials at high risk of bias. [2][4]

Is HMB safe long term?

The ISSN position stand says available data suggest safety up to at least one year, but that comes from a body whose authors disclosed ties to HMB makers. [1] Data for kidney or liver disease, pregnancy and medicine interactions were not found in the sources we read.

Is HMB better than leucine or protein?

In one small trial in young men, HMB added to whey protein gave no more muscle or strength gain than leucine added to whey. [6] For older adults, other illness groups, or HMB against protein alone, proper evidence not found: we searched PubMed for head-to-head trials and did not read a review answering this.

Can HMB replace exercise for muscle loss?

No source we read says so. The older-adult review found extra benefit only modest when added to resistance training. [4]

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

Safety, interactions and cautions
  • The ISSN statement reports no negative effects of either form on glucose tolerance or insulin sensitivity in humans. [1] It is a position of an expert society, not a guarantee for any one person.
  • Medicine interactions, effects in pregnancy and breastfeeding, use in children, and effects in people with kidney or liver disease were not described in the sources we read. We therefore cannot say HMB is safe for these groups; ask a clinician or pharmacist.
  • People with diabetes who take glucose-lowering medicines should discuss any new supplement with their care team.
  • If you compete in tested sport, supplement quality matters: see sport certification and banned substances.
  • Before surgery, tell your surgical team about supplements (supplements before surgery).
References
  1. Rathmacher et al., International Society of Sports Nutrition position stand: beta-hydroxy-beta-methylbutyrate (HMB). J Int Soc Sports Nutr 2025 (online December 2024) (abstract) Read 2026-10-23.
  2. Bear et al., HMB and its impact on skeletal muscle mass and physical function in clinical practice: systematic review and meta-analysis. Am J Clin Nutr 2019 (abstract) Read 2026-10-23.
  3. Lin et al., Effects of oral administration of HMB on lean body mass in older adults: systematic review and meta-analysis. Eur Geriatr Med 2021 (abstract) Read 2026-10-23.
  4. Garcia-Alonso et al., The Role of HMB Supplementation in Enhancing the Effects of Resistance Training in Older Adults: systematic review and meta-analysis. Nutrients 2025 (abstract) Read 2026-10-23.
  5. Bideshki et al., Ergogenic Benefits of HMB Supplementation on Body Composition and Muscle Strength: umbrella review of meta-analyses. J Cachexia Sarcopenia Muscle 2025 (abstract) Read 2026-10-23.
  6. Jakubowski et al., Equivalent Hypertrophy and Strength Gains in HMB- or Leucine-supplemented Men. Med Sci Sports Exerc 2019 (abstract) Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.