Last Updated: November 2 2022

HMB is a metabolite of the essential amino acid leucine that plays an anticatabolic role in muscle tissue. In addition to preventing muscle protein breakdown, HMB may help improve strength and muscle mass in older adults, but evidence of a benefit for athletes is lacking.

HMB is most often used for

What is HMB?

HMB is short for hydroxymethylbutyrate or ꞵ-hydroxy ꞵ-methylbutyrate. It is an active metabolite of the essential amino acid leucine. All of the HMB present in the human body is derived from dietary sources of leucine, with about 5% of all dietary leucine being converted to HMB.[1] HMB is thought to help reduce muscle protein breakdown and may mediate some of the effects of leucine on muscle protein synthesis.

What are HMB’s main benefits?

HMB plays an anticatabolic role in muscle tissue. In other words, HMB prevents muscle protein breakdown and reduces the loss of fat-free mass. These effects seem to be most pronounced during catabolic states, including cancer cachexia,[2] acquired immunodeficiency syndrome (AIDS),[3] and aging.[4][5] HMB seems to be particularly effective for preventing the age-related loss of muscle mass and for preserving strength and body composition in bedridden or sedentary older adults.[4][5]

HMB stimulates muscle protein synthesis, but supplementation fails to increase fat-free mass, improve body composition, or increase measures of strength performance in athletes and trained individuals, and its use in these populations cannot be recommended.[6][7][8] HMB may be effective for reducing exercise-associated muscle damage after high-intensity exercise.[9]

What are HMB’s main drawbacks?

Supplementing with HMB at a dose of 3 grams per day appears to be well tolerated and is not associated with any adverse side effects.[10] This is the dose commonly used in research studies. Higher doses may be equally safe, but very few studies have investigated doses of HMB above 3 grams per day. One study found that 6 grams of HMB per day didn’t cause any concerning changes to cholesterol, blood glucose, red or white blood cells, and liver or kidney function.[11] HMB also appears to be safe when taken with other amino acids (i.e., arginine, lysine, and glutamine) or supplemented alongside creatine.[12][10][9]

How does HMB work?

HMB’s effects on skeletal muscle appear to be due to its actions on both muscle protein synthesis and muscle protein breakdown. HMB promotes muscle protein synthesis by stimulating mammalian target of rapamycin (mTOR), which regulates cell growth and differentiation.[13] HMB may also increase the activity of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis.[14]

HMB reduces protein degradation (protein breakdown) by inhibiting the activity of the body’s ubiquitin-proteasome system and caspases. These two pathways are responsible for breaking down proteins (proteolysis) under catabolic states such as fasting, immobilization, disuse, aging, and disease.[15][16][17] Inhibiting protein breakdown explains why HMB can minimize the loss of lean body mass in certain conditions.

What else is HMB known as?
Note that HMB is also known as:
  • Hydroxy-MethylButyrate
  • beta-hydroxy-beta-methylbutyrate
HMB should not be confused with:
Dosage information

Supplementation of HMB tends to be in the dosage range of 1-3g daily for the purpose of reducing muscle mass losses over time (anti-catabolic). As HMB is said to be 20-fold more potent than leucine for this purpose, it is seen as equivalent to 20-60g of leucine supplementation.

For the purpose of muscle protein synthesis, HMB and leucine are fairly equivalent if not the latter (leucine) being more potent on a gram basis. HMB is not advised for inducing muscle protein synthesis since leucine is likely more effective as well as cheaper.

Supplementation of HMB prior to an exercise session would require the usage of an HMB free acid rather than a calcium salt, and the above dosage range still holds. For this specific purpose, HMB is to be taken 30-45 minutes before a workout.

Supplements Demystified: Get Our Unbiased, Evidence-Based Guide

Examine Database: HMB
What works and what doesn't?

Unlock the full potential of Examine

Get started

Don't miss out on the latest research

1.^Nissen S, Sharp R, Ray M, Rathmacher JA, Rice D, Fuller JC, Connelly AS, Abumrad NEffect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training.J Appl Physiol (1985).(1996-Nov)
4.^Nicolas de Angelus Costa Riela, Maiara Moeme Alvim Guimarães, Daniela Oliveira de Almeida, Edilene Maria Queiroz AraujoEffects of Beta-Hydroxy-Beta-Methylbutyrate Supplementation on Elderly Body Composition and Muscle Strength: A Review of Clinical TrialsAnn Nutr Metab.(2021 Mar 12)
5.^Wu H, Xia Y, Jiang J, Du H, Guo X, Liu X, Li C, Huang G, Niu KEffect of beta-hydroxy-beta-methylbutyrate supplementation on muscle loss in older adults: a systematic review and meta-analysis.Arch Gerontol Geriatr.(2015)
6.^Josephine S Jakubowski, Everson A Nunes, Filipe J Teixeira, Victoria Vescio, Robert W Morton, Laura Banfield, Stuart M PhillipsSupplementation 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-AnalysisNutrients.(2020 May 23)
7.^Holland BM, Roberts BM, Krieger JW, Schoenfeld BJDoes HMB Enhance Body Composition in Athletes? A Systematic Review and Meta-analysis.J Strength Cond Res.(2022-Feb-01)
9.^Jacob M Wilson, Peter J Fitschen, Bill Campbell, Gabriel J Wilson, Nelo Zanchi, Lem Taylor, Colin Wilborn, Douglas S Kalman, Jeffrey R Stout, Jay R Hoffman, Tim N Ziegenfuss, Hector L Lopez, Richard B Kreider, Abbie E Smith-Ryan, Jose AntonioInternational Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB)J Int Soc Sports Nutr.(2013 Feb 2)
10.^Rathmacher JA, Nissen S, Panton L, Clark RH, Eubanks May P, Barber AE, D'Olimpio J, Abumrad NNSupplementation with a combination of beta-hydroxy-beta-methylbutyrate (HMB), arginine, and glutamine is safe and could improve hematological parameters.JPEN J Parenter Enteral Nutr.(2004)
11.^Gallagher PM, Carrithers JA, Godard MP, Schulze KE, Trappe SWBeta-hydroxy-beta-methylbutyrate ingestion, part II: effects on hematology, hepatic and renal function.Med Sci Sports Exerc.(2000-Dec)
15.^Lecker SH, Jagoe RT, Gilbert A, Gomes M, Baracos V, Bailey J, Price SR, Mitch WE, Goldberg ALMultiple types of skeletal muscle atrophy involve a common program of changes in gene expression.FASEB J.(2004-Jan)
20.^Nissen S, Sharp R, Ray M, Rathmacher JA, Rice D, Fuller JC Jr, Connelly AS, Abumrad NEffect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise trainingJ Appl Physiol.(1996 Nov)
22.^Vukovich MD, Slater G, Macchi MB, Turner MJ, Fallon K, Boston T, Rathmacher Jbeta-hydroxy-beta-methylbutyrate (HMB) kinetics and the influence of glucose ingestion in humansJ Nutr Biochem.(2001 Nov)
24.^Gallagher PM, Carrithers JA, Godard MP, Schulze KE, Trappe SWBeta-hydroxy-beta-methylbutyrate ingestion, Part I: effects on strength and fat free massMed Sci Sports Exerc.(2000 Dec)
25.^Wilson JM, Grant SC, Lee SR, Masad IS, Park YM, Henning PC, Stout JR, Loenneke JP, Arjmandi BH, Panton LB, Kim JSBeta-hydroxy-beta-methyl-butyrate blunts negative age-related changes in body composition, functionality and myofiber dimensions in ratsJ Int Soc Sports Nutr.(2012 Apr 18)
26.^Kim JS, Park YM, Lee SR, Masad IS, Khamoui AV, Jo E, Park BS, Arjmandi BH, Panton LB, Lee WJ, Grant SCβ-hydroxy-β-methylbutyrate did not enhance high intensity resistance training-induced improvements in myofiber dimensions and myogenic capacity in aged female ratsMol Cells.(2012 Nov)
29.^Fuller JC Jr, Baier S, Flakoll P, Nissen SL, Abumrad NN, Rathmacher JAVitamin D status affects strength gains in older adults supplemented with a combination of β-hydroxy-β-methylbutyrate, arginine, and lysine: a cohort studyJPEN J Parenter Enteral Nutr.(2011 Nov)
31.^Kornasio R, Riederer I, Butler-Browne G, Mouly V, Uni Z, Halevy OBeta-hydroxy-beta-methylbutyrate (HMB) stimulates myogenic cell proliferation, differentiation and survival via the MAPK/ERK and PI3K/Akt pathwaysBiochim Biophys Acta.(2009 May)
32.^Peterson AL, Qureshi MA, Ferket PR, Fuller JC JrIn vitro exposure with beta-hydroxy-beta-methylbutyrate enhances chicken macrophage growth and functionVet Immunol Immunopathol.(1999 Jan 4)
33.^Siwicki AK, Fuller JC Jr, Nissen S, Ostaszewski P, Studnicka MIn vitro effects of beta-hydroxy-beta-methylbutyrate (HMB) on cell-mediated immunity in fishVet Immunol Immunopathol.(2000 Oct 31)
36.^Pimentel GD, Rosa JC, Lira FS, Zanchi NE, Ropelle ER, Oyama LM, Oller do Nascimento CM, de Mello MT, Tufik S, Santos RVβ-Hydroxy-β-methylbutyrate (HMβ) supplementation stimulates skeletal muscle hypertrophy in rats via the mTOR pathwayNutr Metab (Lond).(2011 Feb 23)
38.^Krajnak K, Waugh S, Miller R, Baker B, Geronilla K, Alway SE, Cutlip RGProapoptotic factor Bax is increased in satellite cells in the tibialis anterior muscles of old ratsMuscle Nerve.(2006 Dec)
39.^Jejurikar SS, Henkelman EA, Cederna PS, Marcelo CL, Urbanchek MG, Kuzon WM JrAging increases the susceptibility of skeletal muscle derived satellite cells to apoptosisExp Gerontol.(2006 Sep)
40.^Tews DS, Goebel HHDNA-fragmentation and expression of apoptosis-related proteins in muscular dystrophiesNeuropathol Appl Neurobiol.(1997 Aug)
41.^Tidball JG, Albrecht DE, Lokensgard BE, Spencer MJApoptosis precedes necrosis of dystrophin-deficient muscleJ Cell Sci.(1995 Jun)
43.^Aversa Z, Bonetto A, Costelli P, Minero VG, Penna F, Baccino FM, Lucia S, Rossi Fanelli F, Muscaritoli Mβ-hydroxy-β-methylbutyrate (HMB) attenuates muscle and body weight loss in experimental cancer cachexiaInt J Oncol.(2011 Mar)
44.^Pugazhenthi S, Nesterova A, Sable C, Heidenreich KA, Boxer LM, Heasley LE, Reusch JEAkt/protein kinase B up-regulates Bcl-2 expression through cAMP-response element-binding proteinJ Biol Chem.(2000 Apr 14)
45.^Green DRApoptotic pathways: ten minutes to deadCell.(2005 Jun 3)
46.^Pinheiro CH, Gerlinger-Romero F, Guimarães-Ferreira L, de Souza-Jr AL, Vitzel KF, Nachbar RT, Nunes MT, Curi RMetabolic and functional effects of beta-hydroxy-beta-methylbutyrate (HMB) supplementation in skeletal muscleEur J Appl Physiol.(2012 Jul)
47.^Wilson JM, Kim JS, Lee SR, Rathmacher JA, Dalmau B, Kingsley JD, Koch H, Manninen AH, Saadat R, Panton LBAcute and timing effects of beta-hydroxy-beta-methylbutyrate (HMB) on indirect markers of skeletal muscle damageNutr Metab (Lond).(2009 Feb 4)
48.^Wilson JM, Lowery RP, Joy JM, Walters JA, Baier SM, Fuller JC, Stout JR, Norton LE, Sikorski EM, Wilson SM, Duncan NM, Zanchi NE, Rathmacher Jβ-Hydroxy-β-methylbutyrate free acid reduces markers of exercise-induced muscle damage and improves recovery in resistance-trained menBr J Nutr.(2013 Jan 3:1-7)
53.^Paddon-Jones D, Keech A, Jenkins DShort-term beta-hydroxy-beta-methylbutyrate supplementation does not reduce symptoms of eccentric muscle damageInt J Sport Nutr Exerc Metab.(2001 Dec)
57.^Wilkinson DJ, Hossain T, Hill DS, Phillips BE, Crossland H, Williams J, Loughna P, Churchward-Venne TA, Breen L, Phillips SM, Etheridge T, Rathmacher JA, Smith K, Szewczyk NJ, Atherton PJEffects of Leucine and its metabolite, β-hydroxy-β-methylbutyrate (HMB) on human skeletal muscle protein metabolismJ Physiol.(2013 Apr 8)
59.^Portal S, Zadik Z, Rabinowitz J, Pilz-Burstein R, Adler-Portal D, Meckel Y, Cooper DM, Eliakim A, Nemet DThe effect of HMB supplementation on body composition, fitness, hormonal and inflammatory mediators in elite adolescent volleyball players: a prospective randomized, double-blind, placebo-controlled studyEur J Appl Physiol.(2011 Sep)
60.^Slater G, Jenkins D, Logan P, Lee H, Vukovich M, Rathmacher JA, Hahn AGBeta-hydroxy-beta-methylbutyrate (HMB) supplementation does not affect changes in strength or body composition during resistance training in trained menInt J Sport Nutr Exerc Metab.(2001 Sep)
63.^Zanchi NE, Nicastro H, Lancha AH JrPotential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studiesNutr Metab (Lond).(2008 Jul 17)
64.^Dardevet D, Sornet C, Balage M, Grizard JStimulation of in vitro rat muscle protein synthesis by leucine decreases with ageJ Nutr.(2000 Nov)
69.^Aversa Z, Alamdari N, Castillero E, Muscaritoli M, Rossi Fanelli F, Hasselgren POβ-Hydroxy-β-methylbutyrate (HMB) prevents dexamethasone-induced myotube atrophyBiochem Biophys Res Commun.(2012 Jul 13)
70.^Jiang Y, Singh P, Yin H, Zhou YX, Gui Y, Wang DZ, Zheng XLOpposite roles of myocardin and atrogin-1 in L6 myoblast differentiationJ Cell Physiol.(2013 Mar 22)
73.^Deutz NE, Pereira SL, Hays NP, Oliver JS, Edens NK, Evans CM, Wolfe RREffect of β-hydroxy-β-methylbutyrate (HMB) on lean body mass during 10 days of bed rest in older adultsClin Nutr.(2013 Mar 4)
74.^Stein TP, Schluter MD, Leskiw MJ, Boden GAttenuation of the protein wasting associated with bed rest by branched-chain amino acidsNutrition.(1999 Sep)
75.^Stein TP, Donaldson MR, Leskiw MJ, Schluter MD, Baggett DW, Boden GBranched-chain amino acid supplementation during bed rest: effect on recoveryJ Appl Physiol.(2003 Apr)
80.^Jówko E, Ostaszewski P, Jank M, Sacharuk J, Zieniewicz A, Wilczak J, Nissen SCreatine and beta-hydroxy-beta-methylbutyrate (HMB) additively increase lean body mass and muscle strength during a weight-training programNutrition.(2001 Jul-Aug)
83.^Baxter JH, Carlos JL, Thurmond J, Rehani RN, Bultman J, Frost DDietary toxicity of calcium beta-hydroxy-beta-methyl butyrate (CaHMB)Food Chem Toxicol.(2005 Dec)
86.^Gallagher PM, Carrithers JA, Godard MP, Schulze KE, Trappe SWBeta-hydroxy-beta-methylbutyrate ingestion, part II: effects on hematology, hepatic and renal functionMed Sci Sports Exerc.(2000 Dec)
87.^Nissen S, Sharp RL, Panton L, Vukovich M, Trappe S, Fuller JC Jrbeta-hydroxy-beta-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factorsJ Nutr.(2000 Aug)
88.^Rathmacher JA, Nissen S, Panton L, Clark RH, Eubanks May P, Barber AE, D'Olimpio J, Abumrad NNSupplementation with a combination of beta-hydroxy-beta-methylbutyrate (HMB), arginine, and glutamine is safe and could improve hematological parametersJPEN J Parenter Enteral Nutr.(2004 Mar-Apr)