Does HMB work or not?

It depends on who for. The ISSN position stand supports it at 38 mg per kilo a day and describes increases in lean mass and function in sedentary older adults. A later meta-analysis focused only on trained and competitive athletes finds no effect on any strength or body composition variable. If you already train seriously, the second body of evidence is the one that applies to you.

Calcium HMB or free acid?

Free acid may be absorbed and retained better, but the ISSN position stand itself says research on that form is early and there is not enough data to call it superior. Paying more for it is paying for a hypothesis.

Does HMB help keep muscle when cutting?

It is its most plausible argument: protecting muscle in situations of loss. Where it is described most clearly is in sedentary older adults. In trained athletes dieting, the specific meta-analysis does not find the effect.

How much leucine do you need to get HMB?

HMB is produced in the body from dietary leucine, although only a small fraction of leucine ends up converted. That is why you cannot reach study doses by eating protein, and also why it makes no sense to buy it before your daily protein is covered.

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HMB · Weak evidence

What HMB is for and what the evidence says

The short answer. HMB is a leucine metabolite sold as a muscle protector. Here two bodies of evidence clash and both are worth seeing. The ISSN position stand supports it at 38 mg per kilo a day for recovery, strength and mass. A later meta-analysis, restricted to trained and competitive athletes, finds no effect at all: not on bench press, leg press, lean mass or fat. The reasonable reading is that where it may make sense is in people who do not train or are losing muscle, not in those who already train seriously.

Reviews find no consistent effect. It is listed because it sells, not because it works. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of HMB with their source
Effect	How much	Detail
Bench press strength (trained)	ES 0.00	Zero. The meta-analysis of six trials with 193 trained and competitive participants finds nothing, with zero heterogeneity, meaning the studies agree in finding nothing. [2]
Leg press strength (trained)	ES 0.09	Trivial and not significant, like the rest of the variables in the same analysis. [2]
Fat-free mass (trained)	ES 0.16	Not significant either. The result held when split by dose, duration, training level and diet. [2]
Position stand dose	38 mg/kg/day	About 2.7 g a day for 70 kg. It is the dose at which the ISSN describes improvements in hypertrophy, strength and power in trained and untrained populations with an adequate training stimulus. [1]
Sedentary older adults	increase in lean mass	The position stand reports increased lean mass and function in older, sedentary people. It is the scenario that makes the most sense: protecting muscle, not adding it on top of training that already works. [1]

02 How to take it

Dose. 38 mg per kilo a day, about 3 g for a 70 kg person, split into several servings.
When. The position stand suggests taking it close to training and starting about two weeks before the demanding period.
How long before you notice it. Around two weeks of prior use, according to the position stand. In trained athletes the meta-analysis finds no effect, short or long term.

Details that change the result

There are two forms: calcium HMB and free acid HMB. The free acid may be absorbed better, but the position stand itself says there is not enough research to declare one superior.
It is expensive for what it offers. For the same money, protein and creatine have a different level of support.
If you already eat enough protein, dietary leucine is already there, and HMB is a metabolite of that leucine.
Safety is not the issue: chronic use is described as safe in young and older people.

03 When it makes sense and when it does not

Worth it if

Sedentary older people or those at risk of losing muscle mass, where the position stand describes gains in lean mass and function.
Periods of forced rest or aggressive weight loss, where the goal is to keep muscle rather than gain it.

Not worth it if

Trained or competitive athletes: the specific meta-analysis in that group finds no effect on strength or body composition.
As a substitute for eating enough protein, which is where the leucine HMB derives from comes from.
Before you have creatine and protein covered, which cost less and have more support.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Wilson JM et al. International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB). J Int Soc Sports Nutr. 2013;10:6. 38 mg/kg de peso corporal al dia; consumo durante 2 semanas antes del esfuerzo; aumento de masa magra y funcionalidad en poblacion mayor sedentaria; sin datos suficientes para preferir HMB calcico o acido libre. doi:10.1186/1550-2783-10-6
Sanchez-Martinez J, Santos-Lozano A, Garcia-Hermoso A, Sadarangani KP, Cristi-Montero C. 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;21(7):727-735. Seis estudios, 193 participantes: efectos triviales y no significativos en press de banca (0,00), prensa de piernas (0,09), peso (-0,01), masa libre de grasa (0,16) y masa grasa (-0,20). doi:10.1016/j.jsams.2017.11.003

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about HMB

Answered with the data on this page

Does HMB work or not?: It depends on who for. The ISSN position stand supports it at 38 mg per kilo a day and describes increases in lean mass and function in sedentary older adults. A later meta-analysis focused only on trained and competitive athletes finds no effect on any strength or body composition variable. If you already train seriously, the second body of evidence is the one that applies to you.
Calcium HMB or free acid?: Free acid may be absorbed and retained better, but the ISSN position stand itself says research on that form is early and there is not enough data to call it superior. Paying more for it is paying for a hypothesis.
Does HMB help keep muscle when cutting?: It is its most plausible argument: protecting muscle in situations of loss. Where it is described most clearly is in sedentary older adults. In trained athletes dieting, the specific meta-analysis does not find the effect.
How much leucine do you need to get HMB?: HMB is produced in the body from dietary leucine, although only a small fraction of leucine ends up converted. That is why you cannot reach study doses by eating protein, and also why it makes no sense to buy it before your daily protein is covered.

And now, which to buy

Prices, kept apart from the evidence

This page explains what HMB does and deliberately names no brand. The comparison is the other half: 13 products from 4 stores from €0.131 per capsule, sorted by price and by how verifiable their certification is.

See the hmb comparison

Other guides

What each supplement does, with its sources