HMB is a metabolite that is naturally found in foods like dairy products, poultry, and other foods that contain protein. It’s also a dietary supplement that is frequently said to have benefits for muscles and body composition.
HMB stands for hydroxy-methylbutyrate (and sometimes beta-hydroxy-beta-methylbutyrate). It’s a metabolite of leucine, one of the essential amino acids.
Leucine comes from foods that contain complete proteins, like meat, seafood, poultry, and dairy products. It’s also found in some plant-based proteins, including soy, lentils, and navy beans. Of the leucine that’s typically consumed, only about 5% gets turned into HMB in the body. This amount isn’t enough to have muscle benefits on its own. That’s why it’s formulated as a dietary supplement, to allow for a concentrated intake.
HMB is not new—it’s been studied for several decades and has been the subject of more than a hundred clinical trials. But that doesn’t mean the level of evidence for every benefit is robust. The following are the most frequently discussed benefits.
Muscles are built from amino acids, which come from proteins. Since HMB is a metabolite of an amino acid, it’s been studied frequently for its possible impacts on muscle mass. Here’s what we know:
A study of 50 participants evaluated HMB’s impact on muscle wasting in people who spent extended time in the hospital. The results did not identify any definite benefits and notes that HMB’s impact on muscle mass remains uncertain.
A randomized controlled trial of 34 older adults evaluated the effects of HMB supplementation along with resistance training in a 12-week program. At the end of the study, the HMB group had better handgrip strength, gait speed, and muscle quality compared to the placebo group. There were no between group differences in skeletal muscle mass or other body composition measurements.
A study of 269 postmenopausal people compared the effects of HMB supplementation with various intervention combinations. After the 12-week study period, HMB showed no additional muscle quality benefits compared to resistance training. Researchers concluded that in this age and gender group, HMB was not useful for supporting muscle quality.
A study of 60 participants who had bariatric surgery, which has a high association with protein malabsorption and changes to muscle mass, compared HMB to both short-peptides and complex protein formulas. The interventional study sought to determine which of the formulas had the best outcome for preserving fat-free mass. The results found that short-peptides were more effective HMB or complex protein.
Overall, there are mixed results on how HMB affects muscle mass. While HMB is well tolerated, it is less proven for muscle mass support than protein supplements, which contain multiple amino acids.
There’s not as much data on how HMB directly affects weight or body fat composition.
A 12-week study of 62 older participants compared a high-protein nutrition shake that included HMB with nutritional counseling for protein balance. The results found that the shake had a significantly greater beneficial effect for body fat composition and muscle mass, as well as nutritional status and physical performance compared to the group who received only nutritional counseling. However, this does not mean that HMB was responsible for the difference in outcome, although it’s possible that it contributed. Larger studies that compare HMB directly with a placebo are needed to evaluate how HMB affects body fat and muscle balance.
A study of 20 postmenopausal people compared L-glutamine, L-arginine, HMB, and MCT oil to placebo. Study outcomes included laboratory markers, body composition measurements, and skin health. After 4 weeks, the group who received the supplement had statistically significant improvements in visceral adipose tissue, body fat composition, maintenance of muscle mass, and improved skin health, while the placebo group did not. However, it’s difficult to know whether HMB contributed to any or all of these outcomes since there were several nutrients involved. With a small sample size, larger studies are needed to evaluate the consistency of these benefits.
To truly understand how HMB may influence body composition or healthy weight balance, it needs to be studied on its own with a placebo control. It’s currently unclear whether HMB plays a direct role in body composition parameters.
HMB could potentially support exercise performance, since various amino acids have been shown to support stamina and athletic outcomes. But the evidence for HMB alone supporting exercise performance is sparse.
A 12-day study of 40 teenage athletes compared HMB, paired with L-arginine (an amino acid), to placebo. Those who took the supplements experienced a slight improvement in performance, but there were no differences between the groups on muscle markers or mood. It’s hard to determine whether HMB, L-arginine, or the combination, may have had the slight benefit. Larger, longer studies are needed with HMB alone to understand if it can impact exercise or training performance in young athletes.
A study of 53 people born male compared HMB with other supplements derived from leucine, as well as a placebo control. The study participants were all involved with resistance training and consumed a high protein diet. The results found that 8 weeks of HMB and other leucine derivatives had no effect on exercise performance, strength, or body composition under these circumstances.
Within the context of muscle repair after exercise strain or damage, though, HMB may have some potential benefits. A systematic review and meta-analysis of 18 studies found that HMB supported improvements in markers used to assess muscle damage (creatine kinase and lactate dehydrogenase), especially when consumed for longer than 6 weeks. Still, more research is needed to fully understand the effects on exercise performance and recovery.
There’s little research on HMB’s effect on cognitive health. A meta-analysis that looked at exercise with HMB for muscle health and cognition in aging adults didn’t have human data to support the benefits of HMB for cognition alone.
A study of 148 active duty military airmen found that 12 weeks of fitness and strength training, when paired with a nutritional beverage that included HMB, lutein, phospholipids, DHA, B12, and folic acid, improved working memory, intelligence reaction time, efficiency of information processing, and muscle and heart rate parameters. However, because of the multiple nutrients in this intervention, the study cannot be considered as proof that HMB supports cognition. This is especially true since nutrients that have known cognitive support, like DHA and B12, were part of the supplement.
HMB works by acting on mechanisms involved with cell growth and differentiation, leading to impacts on both muscle protein synthesis and muscle breakdown. Essentially, HMB has anti-catabolic properties. That might make it most useful under circumstances where catabolism might more directly affect the muscles, like aging, malnutrition, reduced mobility, and extended bed rest.
If someone isn’t in a prolonged catabolic state, or if they’re already getting plenty of amino acids from protein, HMB is less likely to have much of an impact.
HMB is generally well tolerated and isn’t known to have safety concerns when taken as directed.
Several studies on HMB report no side effects. One reported a few rare side effects of abdominal pain, constipation, or itching. These are not considered to be common and are not noted in most studies involving HMB.
Always consult your healthcare provider before starting HMB or any dietary supplements. Supplements can interact with other medications, supplements, or over-the-counter products.
If your doctor has suggested HMB or you’re ready to try it, there are some important things to consider when you’re comparing options.
HMB is naturally found in foods that contain protein, because it’s produced in the body after you eat leucine. However, your body doesn’t make much HMB from food-derived sources alone.
HMB has safely been paired with other amino acids, vitamins, and fatty acids in clinical trials. There are no indications that it has direct interactions with other supplements. However, only your medical provider can determine if you should take HMB with other supplements.
HMB is an amino-acid derived supplement that is mostly considered to have muscle-related benefits. Researchers have found mixed results, and HMB tends to show more possible benefits for people who aren’t already athletes or consuming higher protein diets.
If you’re interested in trying HMB to support healthy muscle mass or body composition, check with your doctor to make sure it’s the right option for you. There may be other options that are more effective, like increasing your protein intake with protein powder or focusing on a more nutrient-dense diet.