What is HMB? Uses, Benefits, Safety, and More

Over the past few years, the natural substance HMB has continued to rise in popularity in the sports and fitness world, at least in part, due to the important role it appears to play in muscle protein turnover.

Consequently, HMB can now be found in a variety of different pre-workout supplements and has gained traction amongst professional athletes ranging from hockey players to cross-fitters.

But what is HMB exactly, and is it really a safe and effective supplement? In order to shed light on questions like these, we're going everything from how HMB actually works to what kind of benefits have been associated with HMB supplementation in recent research. But before we get into any of that, let's first discuss what HMB actually is and where it comes from.

What is HMB?

HMB, which is short for β-hydroxy-β-methylbutyrate, is a metabolite of the branched-chain amino acid leucine. While they may have some overlapping functions,  HMB is not to be confused with leucine.  

Your body converts some of the leucine that comes in through your daily diet into HMB, although it’s a relatively small percentage.  While small amounts can be obtained through food sources, it’s also commonly consumed as a dietary supplement.  

How Does HMB Work?

⫸Prevents Muscle Protein Breakdown

The muscles throughout your entire body are actually going through a constant state of flux.  On a microscopic level, your muscles are made up of tiny proteins that are continuously being broken down and resynthesized -- this general process is referred to as muscle protein turnover.  

Your body breaks down muscle tissue because it is constantly in need of amino acids for use in building enzymes, hormones, and other proteins.  Your muscles act like a reservoir for this supply.

Muscle protein breakdown (MPB) is a process that also occurs during and after physical activity like exercise.  HMB works by alters your muscle’s metabolism, decreasing the presence of enzymes like lactate dehydrogenase (LDH), which contribute to the breakdown of muscle proteins. ⁽¹⁾⁽²⁾

⫸Promotes Muscle Protein Synthesis

On the other side of the protein turnover equation is Muscle protein synthesis (MPS). MPS is the process through which your body repairs and rebuilds damaged muscle tissues.  

Physical activity ranging from an intense workout to a leisurely walk can break down muscle proteins, causing microscopic damage to your muscles.  In response, your muscles rely on a set of signaling pathways, which once activated, help to transports the necessary supplies required to make repairs.

HMB has been shown to play an important part in this signaling process, helping to stimulate MPS through the activation of the mammalian target of rapamycin (mTOR) pathway. ⁽³⁾⁽⁴⁾

mTOR plays an important role in a variety of different cellular processes including protein synthesis. Once activated, mTOR helps to coordinate the delivery of nutrients and oxygen to damaged muscle tissues, facilitating the replacement of old, broken down proteins with fresh, new ones.

What Are the Benefits of Taking HMB?

⫸HMB Can Attenuate Muscle Loss

While muscle protein breakdown is a naturally occurring process, if your protein turnover rate is out of balance, it can lead to muscle loss.  In other words, if more muscle proteins are being broken down in your body than rebuilt, over time, your muscle mass will decrease.

Several studies on HMB, however, have found that it can help to attenuate muscle loss in everyone from competitive athletes to elderly folks, especially in combination with resistance training. ⁽⁵⁾

Sports and Muscle Loss

For athletes and anyone going through rigorous physical activity on a daily basis, muscle loss can be a very serious and very real risk, especially if you’re not getting enough rest.  

Supplementing with HMB, on the other hand, has been found to decrease the amount of muscle protein breakdown that occurs during and after exercise, improving recovery time and decreasing the risk of muscle loss for athletes. ⁽⁶⁾

Weight Loss and Body Recomposition

The risk of losing muscle also increases when you’re trying to lose weight.  During a weight loss diet, you’re taking in fewer calories than your body needs over the course of a day.  While this can be effective for shedding excess body fat, it also places your muscles in danger.

When your calorie intake has been restricted, your body will often start breaking down muscle tissue along with fat in order to meet its energy needs.

Multiple studies, however, have found that in combination with adequate protein intake and regular exercise, HMB supplementation helps to preserve lean muscle mass and promote more fat loss during a hypocaloric diet.        

Muscle Loss and Aging

Muscle loss also becomes an increasing risk as you age.  After somewhere around 30, most people naturally begin losing muscle mass.  It’s a relatively slow process, but over the course of a decade, you can lose as much as 5% of your lean body mass.  

By the time you get into your 70’s, those losses can really add up, impacting both your strength and mobility. However, researchers have found that supplementing with HMB can be an effective tool for mitigating age-related muscle loss. ⁽⁷⁾

For example, one study published in the International Journal of Nutrition examined the effects of HMB supplementation on 70-year-old men and women. (8)  

Some study participants were given HMB and others were given a placebo.  After an 8-week, 5-day a week exercise program, the researchers found that compared to the placebo group, the group that was given HMB, on average, not only lost more body fat but they also significantly greater increases in lean body mass.

⫸HMB Can Help You Build Size and Strength

Preventing protein breakdown isn't the only thing HMB is good for either. It also helps to promote muscle protein synthesis, which is the perfect equation for making your muscles bigger and stronger.  

When it comes to bulking up, your muscles only grow when more protein is synthesized than broken down. The only problem is: that's easier said than done, even with proper nutrition and training.

However, because HMB helps to both decrease protein breakdown and increase MPS, it puts your body in an excellent position to build muscle.

In fact, a number of studies have concluded that over time, those who supplemented with HMB saw significantly greater increases in size and strength compared to those who did not. ^(9)(10)

For instance, a study published in the Journal of Nutritional Biochemistry found that in human subjects who regularly participated in resistance training, HMB supplementation helped to increase lean mass gains by as much as 200%. ⁽¹¹⁾ The researchers also found that those who were given HMB saw significantly greater increases in strength as well.

Is HMB Safe?

There are no serious safety concerns associated with HMB supplementation.  Toxicologically speaking, research on both rats and humans illustrates that HMB appears to be tolerated well even at high dosages and over long durations of time.

In the numerous studies conducted on human subjects, no serious short or long-term side effects have been reported up to this point.^(12)(13)

HMB Dosage Recommendations

In the vast majority of HMB-related research, study participants received a dosage of 3g per day.

A position stand paper published by the International Society of Sports Nutrition concluded that 38 mg of HMB per kilogram(kg) of body weight was the ideal daily dose for maximal size and strength gains.⁽¹⁴⁾

So for example, if you weigh 180 lbs that’d be about 82 kgs. If we multiply 38 (mg of HMB) by 82 (kgs of body weight), we get 3116, or 3.1g of HMB per day.

Combining HMB With Creatine (and other supplements)

Due to its positive effects on muscle protein turn over, HMB has become a popular ingredient in pre-workout supplements.  It’s regularly combined with other substances like creatine and beta-alanine (BA) to amplify its effects on muscle protein turnover.  

Creatine helps to boost your body’s level of adenosine triphosphate (ATP), giving your muscles more available energy during physical activity.  BA helps your body produce carnosine, which blocks the build-up of lactic acid during intensive exercise.  

When mixed together with HMB, the combination has been shown to significantly increase both muscle mass and exercise performance in adults ranging from well-trained athletes to novice lifters. ⁽¹⁵⁾

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Wrap Up

HMB is a metabolite of the amino acid leucine which can be found in both food sources and dietary supplements like pre-workouts.  It plays an important role in a number of cellular processes, including protein turnover.

Multiple studies have demonstrated that HMB supplementation helps to both promote muscle protein synthesis and prevent protein breakdown, giving it a variety of applications.

Due to the fact that it aids in preventing muscle loss, HMB may be beneficial for weight loss and body recomposition.  Because it also helps to promote protein synthesis, it can be an effective tool for making size and strength gains as well.  

No serious side effects or health concerns have been found to be associated with HMB supplementation up to this point.  While it can be effective all on its own, HMB is popularly paired with other substances like creatine in order to further enhance its effects.  

• References
  1. “Effects of leucine and its metabolite β‐hydroxy‐β‐methylbutyrate on human skeletal muscle protein metabolism” Wilkinson, D.J., Hossain, T., Hill, D.S., Phillips, B.E., Crossland, H., Williams, J., Loughna, P., Churchward-Venne, T.A., Breen, L., Phillips, S.M., Etheridge, T., Ratchmacher, J.A., Smith, K., Szewczyk, N.J., Artherton, P.J. The Journal of Physiology. Apr. 2013.
  2. “Effect of leucine metabolite β-hydroxy-β-methylbutyrate on muscle metabolism during resistance-exercise training” Nissen, S., Sharp, R., Ray, M., Rathmacher, J.A., Rice, D., Fuller Jr., J.C., Connelly, A.S., Abumrad, N. Journal of Applied Physiology. Nov. 1996.
  3. “Signaling pathways initiated by β-hydroxy-β-methylbutyrate to attenuate the depression of protein synthesis in skeletal muscle in response to cachectic stimuli”Eley, H., Russell, S.T., Baxter, J.H. Mukerji, P., Tisdale, M.J. American Journal of Physiology. Oct. 2007.
  4. “Effects of leucine and its metabolite β‐hydroxy‐β‐methylbutyrate on human skeletal muscle protein metabolism” Wilkinson, D.J., Hossain, T., Hill, D.S., Phillips, B.E., Crossland, H., Williams, J., Loughna, P., Churchward-Venne, T.A., Breen, L., Phillips, S.M., Etheridge, T., Ratchmacher, J.A., Smith, K., Szewczyk, N.J., Artherton, P.J. The Journal of Physiology. Apr. 2013.
  5. “Mechanism of the Attenuation of Proteolysis-Inducing Factor Stimulated Protein Degradation in Muscle by β-Hydroxy-β-Methylbutyrate” Smith, H.J., Wyke, S.M., Tisdale, M.J. Cancer Research. Dec. 2004.
  6. “β-Hydroxy-β-methylbutyrate free acid reduces markers of exercise-induced muscle damage and improves recovery in resistance-trained men” Wilson, J.M., Lowery, R.P., Joy, J.M., Walter, J.A., Baier, S.M., Fuller, J.C., Stout, J.R., Norton, L.E., Sikorski, E.M., Wilson, S.M., Duncan, N.M., Zanchi, N.E., Rathmacher, J. British Journal of Nutrition. Aug. 2013.
  7. “Efficacy of β-hydroxy-β-methylbutyrate supplementation in elderly and clinical populations” Fitschen, P.J., Wilson, G.J., Wilson, J.M., Wilund, K.R. Nutrition. Oct. 2012.
  8. “Body Composition in 70-Year-Old Adults Responds to Dietary β-Hydroxy-β-Methylbutyrate Similarly to That of Young Adults” Vukovich, M.D., Stubbs, N.B., Bohlken, R.M. The Journal of Nutrition. Jul. 2001.
  9. “Nutritional supplementation of the leucine metabolite β-hydroxy-β-methylbutyrate (hmb) during resistance training” Panton, L.B., Rathmacher, J.A., Baier, S., Nissen, S. Nutrition. Sep. 2000.
  10. “The effects of 12 weeks of beta-hydroxy-beta-methylbutyrate free acid supplementation on muscle mass, strength, and power in resistance-trained individuals: a randomized, double-blind, placebo-controlled study” Wilson, J.M., Lowery, R.P., Joy, J.M., Anderson, J.C>, Wilson, S.M., Stout, J.R>, Duncan, N., Fuller, J.C., Baier, S.M., Naimo, M.A., Ratchmacher, J. European Journal of Applied Physiology. Mar. 2014.
  11. “Nutritional role of the leucine metabolite β-hydroxy β-methylbutyrate (HMB)” Nissen, S.L., Abumrad, N.N. The Journal of Nutritional Biochemistry. Jun. 1997.
  12. “β-Hydroxy-β-Methylbutyrate (HMB) Supplementation in Humans Is Safe and May Decrease Cardiovascular Risk Factors” Nissen, S., Sharp, R.L., Panton, L., Vovovich, M., Trappe, S., Fuller Jr., J.C. The Journal of Nutrition. Aug. 2000.
  13. “International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB)” Wilson, J.M., Fitschen, P.J., Campbell, B., Wilson, G.J., Zanchi, N., Taylor, L., Wilborn, C., Kalman, S., Stout, J.R>, Hoffman, J.R>, Ziegenfuss, T.N., Lopez, H.L., Krdider, R.B., Smith-Ryan, A.E., Antonio, J. Journal of the International Society of Sports Nutrition. Feb. 2013.
  14. “International Society of Sports Nutrition Position Stand: beta-hydroxy-beta-methylbutyrate (HMB)” Wilson, J.M., Fitschen, P.J., Campbell, B., Wilson, G.J., Zanchi, N., Taylor, L., Wilborn, C., Kalman, S., Stout, J.R>, Hoffman, J.R>, Ziegenfuss, T.N., Lopez, H.L., Krdider, R.B., Smith-Ryan, A.E., Antonio, J. Journal of the International Society of Sports Nutrition. Feb. 2013.
  15. “Creatine and β-hydroxy-β-methylbutyrate (HMB) additively increase lean body mass and muscle strength during a weight-training program” Jowko, E., Ostaszewski, P., Jank, M., Sacharuk, J., Zieniewicz, A., Wilczak, J., Nissen, S. Nutrition. Jul. 2001.