Quick Navigation


HMB is an active metabolite of leucine that reduces muscle protein breakdown. It appears to have an anticatabolic role for muscle, but fails to be more effective than its parent amino acid for inducing muscle protein synthesis.

Our evidence-based analysis on hmb features 72 unique references to scientific papers.

Research analysis led by .
Reviewed by
Examine.com Team
Last Updated:

Summary of HMB

Primary information, health benefits, side effects, usage, and other important details

HMB (short for β-Hydroxy β-Methylbutyrate) is a metabolite of the amino acid leucine that, along with KIC (α keto-isocaproate) and isovaleryl-CoA, mediate the effects of leucine. Approximately 5% of dietary leucine is oxidized into HMB, and HMB appears to be the main metabolite of leucine that more effectively prevents the breakdown of muscle protein.

When compared to leucine, HMB appears to be significantly more potent on a gram per gram basis at attenuating the rate of muscle protein breakdown but is less effective than leucine at inducing muscle protein synthesis. Due to this, HMB is marketed as an anti-catabolic agent (purposed to reduce the rate of muscle breakdown) rather than an anabolic agent (purposed to increase muscle mass).

Human trials don't normally tend to be structured to properly assess the effects of HMB, as most of the studies are a standard diet paired with an exercise regimen investigating the role of HMB in promoting muscle protein synthesis (of which it is similar to leucine in the sense that there are positive results, but quite unreliably so); the limited evidence that assesses HMB during periods of muscle loss are either underpowered or not in athletes.

HMB, currently, appears to be a pretty interesting supplement for the purpose of reducing muscle wasting during periods where muscle atrophy is accelerated (cachexia, AIDS, bedrest) and should theoretically work in athletes on a calorie restricted diet but is not fully established for this role yet (which is a notable issue, since glutamine has a large dichotomy between clinical and healthy populations).

Want the unbiased truth on building muscle?

Our free muscle building mini-course teaches you what works, what's a waste of time, and advanced tips.

We cover bottlenecks, supplements that actually work, a surprising way you could be limiting your muscle gains, and what you need to do to maximize muscle building.

How to Take

Recommended dosage, active amounts, other details

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.

Easily stay on top of nutrition research

Become an Examine.com member to get access to the latest research. 150+ studies summarized across 25 different categories every month.

Becoming a member also unlocks our study database of 400+ supplements and their effects on 600+ health outcomes.

Already a member? Click here to log in.

Make informed decisions about your health

Human Effect Matrix

Unlocked for Examine members

The Human Effect Matrix summarizes human studies to tell you what effects HMB has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-a - Moderate See all 12 studies
Limited evidence supports the increase in power output, which may be due to chance; more often than not, there is no significant influence
grade-b Notable High See all 3 studies
Decrease creatine kinase exists following acute supplementation (15-30 minutes before a workout) of HMB free acid to about a third of control, and is effective in trained individuals
grade-b Minor Low See all 7 studies
There may be a decrease in fat mass associated with HMB supplementation when combined with resistance training, but this reduction is not a large magnitude and usually does not occur; quite unreliable
grade-b - Very High See all 3 studies
No significant influence on cortisol levels following acute ingestion
grade-b - High See all 4 studies
Although there are sporadic alterations seen in food intake in studies using HMB supplementation, they are not reliable and the exact change observed changes. It is likely that there is no significant effect per se and this is due to the study population
grade-b - High See all 8 studies
No significant influences on lean body mass associated with HMB supplementation
grade-b - Very High See all 3 studies
No significant influence of acute usage on testosterone levels
grade-b - Very High See all 3 studies
No significant influence on training volume when used acutely
grade-c Minor - See 2 studies
One underpowered study noted an increase in total cholesterol while another suggested no significant effect. The exact effect of HMB on total cholesterol is not currently known and required replication
grade-c - - See study
No significant improvement in sprint capacity in trained persons supplementing HMB
grade-c - Very High See 2 studies
Studies that assess bone mineral density via DEXA, albeit short in duration and in athletes rather than populations at risk for osteoporosis, fail to find significant alterations in bone mineral density.
grade-c - - See study
No significant influence on C-reactive protein
grade-c - Very High See 2 studies
No significant reduction in exercise-induced fatigue associated with HMB supplementation in athletes
grade-c - - See study
Serum growth hormone is not significantly altered with HMB supplementation in athletes
grade-c - Very High See 2 studies
No significant influence on HDL cholesterol levels
grade-c - - See study
No significant alterations in circulating IGF-1 concentrations
grade-c - - See study
No significant alterations in circulating IL-6 concentrations
grade-c - Very High See 2 studies
No significant influence on LDL cholesterol levels
grade-c - Very High See 2 studies
No significant alterations in serum liver enzymes are noted with HMB supplementation
grade-c - Very High See 2 studies
No significant influence on perceived muscle soreness following exercise with HMB supplementation
grade-c - - See study
No significant influence on range of motion (impaired in both groups due to soreness post workout)
grade-d Minor - See study
A lone study that is underpowered suggest a decrease in blood glucose (measured by chance during a blood panel); not enough robust evidence supports a reduction in blood glucose but it cannot be ruled out
grade-d Minor - See study
A slight increase in urea has been noted, requires replication
grade-d - - See study
No significant influence on triglycerides
grade-d - - See study
No significant influence on VO2 max in trained athletes

Studies Excluded from Consideration

Stay on top of the latest research

Become an Examine Personalized member to access the latest nutrition research on over 400 supplements across more than 600 different health goals, outcomes, conditions, and more. Information tailored to you, updated every month.

Bonus: unlock the supplement Human Effect Matrix and all health topics on Examine.com.

Frequently Asked Questions and Articles on HMB

Four Testosterone Boosters and Sketchy Research

Things to Note

Primary Function:

Also Known As

Hydroxy-MethylButyrate, beta-hydroxy-beta-methylbutyrate

Do Not Confuse With

Leucine (parent amino acid)

Are you tired of all the misinformation pushed by supplement companies?

We've developed a free muscle building mini-course based on nutrition research to help you understand how to build muscle better. Learn about:

  • What supplements work
  • What supplements are a waste of time and money
  • How antioxidants could be messing up your muscle growth
  • How to maximize muscle growth
Click here to see all 72 references.