HMB has been rising in popularity in the fitness world over the past few years and can now be found in a variety of different pre-workout supplements.  That’s primarily due to the growing cache of research demonstrating that it plays an important role in muscle protein turnover.

The studies suggest that HMB supplementation may be advantageous to everyone from top-level athletes to casual gym-goer.  Before we get too far into the benefits however, let’s first discuss what HMB actually is and what roles it plays in your body.

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’s consumed through your daily diet into HMB, although it’s a pretty meager 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)

Promote Muscle Protein Synthesis

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

While exercise certainly breakdowns lots of muscle proteins, even the tasks you perform throughout your everyday life cause microscopic damage to your muscle tissues which requires repair.  

In order to rebuild, your muscles rely on a set of signaling pathways, which once activated, help to provide your muscles with the supplies they need to be repaired.

 HMB helps to stimulate MPS through the activation of mammalian target of rapamycin (mTOR) pathways. (3)(4)

mTOR plays an important role in a variety of different cellular process 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 new ones.

What Are the Benefits of Taking HMB?

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. (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 is effective for shedding excess body fat, it also places your muscles in danger.

When your calorie intake has been heavily 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 an 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.  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, some research has found HMB supplementation to be an effective tool for addressing 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.  

Some study participants were given HMB and others were given a placebo.  After an 8-week exercise program consisting of 5 days a week of training, the researchers found that compared to the placebo group, the group that was given HMB on average lost more body fat and saw significantly greater increases in lean body mass. (8)

Build Size and Strength

HMB doesn’t only prevent protein breakdown (MPB), it also helps to promote muscle protein synthesis (MPS), which is the perfect equation for making your muscles bigger and stronger.  When it comes to protein turnover, 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 both decrease protein breakdown and increase MPS, it helps create the necessary conditions for muscle growth.  

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 undergoing resistance training, HMB supplementation helped to increase lean mass gains by as much as 200%. (11) The researchers all 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 taking HMB.  Toxicologically, 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 found up to this point.(12)(13)

HMB Dosage Recommendations

Study participants received a daily dosage of 3g per day in the vast majority of HMB-related research on human subjects. A position stand paper published by the International Society of Sports Nutrition concluded that 38 mg of HMB per kilogram(kg) of bodyweight 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 (mgs of HMB) by 82 (kgs of body weight), we get 3116, or 3.1g of HMB per day.

Combining HMB With Creatine (and other ingredients)  

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 MPS and MPB during and after resistance exercise.  

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)

the ultimate HMB stack:

HMB + creatine + beta-alanine + HICA + phosphatidic acid

Learn More

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 wide variety of applications.  

Because it helps to prevent muscle loss, it may be beneficial for weight loss and body recomposition.  Because it also helps to promote protein synthesis, it can also be an effective tool for making size and strength gains.  

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.  

No matter whether you’re trying to shed fat, build muscle, or just maintain what you’ve already got, HMB can help you perform your best inside the gym and look your best outside of it.