HMB: Effects, Benefits and Safety

Key Points:

HMB is a byproduct of the amino acid leucine that reduces muscle breakdown and stimulates muscle protein synthesis.
It is often marketed towards athletes and bodybuilders looking to gain muscle and strength, but research does not support it’s effectiveness in trained individuals.
A typical daily of dosage of HMB is 3 grams per day, and it is a well-tolerated supplement without any apparent side-effects.

After reading this article, you’ll know what HMB is and how it affects your muscles and performance. Also, you’ll know if claims that HMB supplements help you get stronger and build muscle have any scientific basis.

Table of Contents

What Is HMB?

HMB stands for beta-hydroxy-beta-methylbutyrate and is a by-product of the amino acid leucine. When you eat or drink any kind of protein that gives you leucine, your body converts some of it to HMB through a series of advanced processes. Around 5% of the leucine you get from the food you eat ends up as HMB.¹

Leucine, one of the three BCAAs or branched-chain amino acids, is critical when it comes to controlling your muscle tissue. It’s involved in muscle protein synthesis, muscle protein breakdown, and insulin- and blood glucose control. Leucine is also a well-known trigger for muscle protein synthesis. In addition, it reduces muscle breakdown under certain conditions. HMB mainly works by reducing muscle breakdown, although it also stimulates muscle protein synthesis to a degree.²

Because your body only creates small amounts of HMB, you can also get HMB as a dietary supplement. A typical dosage in studies is 3 grams of HMB per day. To get that much from your food, you’d need to eat enough protein to get 60 grams of leucine, and that would be quite a challenge. Eating 100 grams of a quality protein source like eggs, fish, or meat gives you between 1 to 2 grams of leucine.

The Effects of HMB on Strength and Body Composition

Numerous studies look at the effects of HMB supplements on muscle strength and body composition, both in trained and untrained individuals. Some find positive outcomes, while others conclude that HMB doesn’t add anything to the effects of the training itself.

Single Studies

In an early study from 1999, 40 experienced strength athletes supplemented their diet with either 0, 3, or 6 grams of HMB during 28 days of regular resistance training.

Research Reviews and Meta-Analyses

To date, one review article and four meta-analyses compile the available HMB research looking for scientific evidence supporting changes in performance and body composition. The review article is quite old, from a time where there were only two peer-reviewed articles available.³ It’s likely not very relevant or valuable anymore.

The 2009 Meta-Analysis

The first of the meta-analyses came out in 2009. It gathers data from nine studies looking at the effects of HMB on strength, fat-free mass, body fat, and markers of muscle breakdown in trained and untrained men.⁴

The researchers found small but significant gains in lower body strength when previously untrained men supplemented with HMB. However, they only saw a trivial effect on upper body strength, and HMB had a minimal impact on both upper- and lower body strength in trained lifters.

The meta-analysis concluded the average strength gains from using HMB to be 3.7±2.4%, which the researchers deemed trivial. They found that the effects of HMB on muscle mass are also insignificant at best, regardless of training experience.

The 2018 Meta-Analysis

In 2018, another meta-analysis saw the light of day and examined if HMB is effective in improving strength and body composition in trained and competitive athletes.⁵ The researchers gathered data from randomized controlled trials measuring leg press or bench press strength, body mass, fat-free mass, and body fat. In the end, six studies with 193 participants qualified for inclusion.

The results of the meta-analysis indicates that HMB does not significantly improve leg press or bench press performance in trained athletes. Also, the researchers did not find any changes in total body mass, fat-free mass, or body fat attributed to HMB. They then looked at HMB dosage, training experience, and the duration of the supplementation. Still, the results didn’t change: HMB did not affect strength or body composition in any significant way.

hmb supplement — _{J Sci Med Sport. 2018 Jul;21(7):727-735. Effects of beta-hydroxy-beta-methylbutyrate supplementation on strength and body composition in trained and competitive athletes: A meta-analysis of randomized controlled trials.}

Looking at the forest plot above you can see that HMB does not affect bench press strength, leg press strength, fat-free mass, body mass, and body fat. The diamonds at the bottom of the forest plots show the combined average result of all included studies. As you can see, the “no effect”-line in the middle passes through the diamond every time.

The First 2019 Meta-Analysis

Right before Christmas of 2019, another meta-analysis showed up.⁶ It examined the effects of HMB on body composition, meaning body fat and fat-free mass, in athletes.

After eliminating several studies failing to meet the inclusion criteria, seven studies looking at total body mass, five looking at fat-free mass, and five looking at body fat remained. Some of them overlapped, looking at more than one thing. The studies lasted at least four weeks, and every participant was considered an athlete.

Like the previous meta-analysis, this one found no effects of HMB on body fat or total body mass. However, the researchers found a small but significant impact on fat-free mass. Compiling all the data showed that athletes might improve their fat-free mass a little by supplementing with HMB.

Importantly, this positive effect of HMB disappeared entirely when the participants ate 1.6 grams of protein per kilogram of body weight per day. That suggests that you only benefit from HMB if you don’t eat a high-protein diet. And since athletes looking to build muscle should probably eat that amount of protein per day anyway, the benefits of HMB for gaining muscle remain dubious.

The Second 2019 Meta-Analysis

In 2019, we did not get just one meta-analysis of HMB, but two. The second one looked at combining HMB and physical exercise on body composition, strength, and muscle mass in older people.⁷ It compiled data from randomized controlled trials with 384 participants between the ages of 50 and 80. The results show trivial or no effects at all from supplementing with HMB at an older age.

The 2020 Meta-Analysis

Lastly, a 2020 systematic review and meta-analysis investigated the efficacy of HMB supplementation in augmenting fat-free mass and strength gains during weight training in young adults.⁸ It did not find any significant effects of HMB on lean muscle mass, fat mass, or strength. The researchers conclude that there is no reason for young athletes who want to build muscle and gain strength to use an HMB supplement.

In summary, a few studies show positive effects and improvements in strength and muscle mass from HMB supplements, especially in untrained individuals. However, the scientific evidence as a whole suggests that those effects are trivial at best. Meta-analysis compiling the results of all available research shows that any effects of HMB in trained individuals and athletes are so minor as to be non-existent or only evident when eating a low-protein diet.

The Wilson Study

In 2014, HMB went from being a promising dietary supplement to a white-hot one. That year, the study The effects of 12 weeks of ß-Hydroxy-ß-methylbutyrate free acid supplementation on muscle mass, strength, and power in resistance-trained individuals: a randomized, double-blind, placebo-controlled study, was published.⁹ The participants experienced extremely impressive gains in strength and muscle mass after 12 weeks of HMB supplementation in combination with strength training. They gained as much muscle mass as previously shown in strength-training men injecting 600 mg of testosterone per week.

Two years later, in 2016, the same researchers published another study on HMB. This time, the combination of HMB and ATP resulted in trained athletes gaining 12.7% muscle in 12 weeks while simultaneously improving strength and peak power tremendously.¹⁰

I could dissect these two studies and speculate why their results are superior to every other published HMB study. However, such speculation would only be hearsay and rumors without substantial evidence, and I don’t want to engage in such things. Let’s just say that other experts do not accept these studies in the field. Also, the latest HMB meta-analyses do not include them.

In 2017, other scientists published a letter discussing the limitations and strange results of the studies.¹¹ The researcher responsible for the HMB studies responded to that letter, but the reply didn’t clarify things satisfactorily.¹²

The International Society of Sports Nutrition Position Stand from 2013

In 2013, the International Society of Sports Nutrition published a position stand on the use of HMB as a nutritional supplement.¹³ They concluded that HMB enhances muscle hypertrophy, strength, and power in untrained and trained individuals.

It should be noted that all later meta-analyses fail to come the same conclusion, and that the ISSN position stand was headed by the researcher behind the dubious 2014 and 2016 studies mentioned above.

Effects of HMB on Exercise-Induced Muscle Damage

According to the available research, HMB might not be beneficial for building muscle, but many athletes also use it to reduce muscle breakdown from exercise and speed up recovery.

Another recent meta-analysis gathers data from studies documenting these effects, looking at creatine kinase and lactate dehydrogenase in particular.¹⁴ Those are two markers for muscle damage and muscle breakdown. There is no easy way to measure muscle breakdown during and after exercise, so researchers have to look at indirect markers instead.

For the meta-analysis, the researchers found ten relevant studies measuring creatine kinase levels and eight studies measuring lactate dehydrogenase after a strength-training session in healthy individuals using HMB.

They found that randomized controlled trials with a total of 324 participants showed that HMB significantly lowers the levels of both creatine kinase and lactate dehydrogenase. That suggests reduced muscle breakdown after training and that HMB might help restore optimal muscle function after a workout.

HMB in Clinical Trials

Let’s look outside the gym for a moment. Supplementing with HMB might reduce muscle loss and muscle weakness in several medical conditions.

A recent meta-analysis found that supplementing with HMB led to a significant increase in muscle mass and strength in patients with HIV, cancer cachexia, rheumatoid arthritis, chronic obstructive pulmonary disease, and people on hemodialysis.¹⁵ The effect size, both for body composition and functional capacity, was pretty small, but even minor improvements might mean a lot for patients with these diseases. Even if they are barely measurable in healthy athletes, they might benefit individuals suffering from severe medical conditions.

Do You Benefit from HMB during Calorie Restriction?

HMB is often promoted as a supplement for building muscle, but can it help your weight loss during a cut as well?

In a 2010 study, eight female judo athletes split into two smaller groups, one of which received 3 grams of HMB per day while the other received placebo pills containing cellulose.¹⁶ After three days of calorie restriction, the HMB group lost significant body weight and fat, and the control group did not lose any fat. Muscle mass and performance remained the same in both groups.

In other words, supplementing with HMB during energy restriction might help you lose body fat. If better studies replicate these results, that is. The 2010 study is way too short with too few participants, dramatically limiting the evidence’s quality.

Hormonal Effects of HMB

Does HMB affect your hormones? Let’s take a look at the evidence?

In one study, elite youth volleyball players between the age of 13.5 to 18 received 3 grams of HMB per day for seven weeks. There were no noticeable hormonal changes.

In summary, HMB supplements do not seem to influence anabolic or catabolic hormones in any significant way in adolescents or adults. The one exception might be the growth hormone response to exercise, as demonstrated in one study, but it was likely small enough to make little difference in practice. Also, previous research shows that minor to moderate elevations in growth hormone levels do not lead to muscle growth.¹⁷

Different Types of HMB

The two significant types of HMB supplements on the market are calcium salt forms and free acid forms. Most studies on HMB use calcium HMB. HMB levels in the blood increase a lot faster with the free acid form of HMB than the calcium-bound version. Also, the time it takes for HMB to leave your blood is shorter with the free form. That suggests a more rapid uptake and availability compared to calcium HMB.¹⁸

The notorious 2014 study that found dramatic increases in strength and muscle mass due to HMB supplementation used free HMB. That made many people think that free HMB might be superior to calcium HMB and explain why previous studies hadn’t found HMB valuable for gaining strength and mass.

However, a 2017 study showed that both calcium HMB and free HMB activate anabolic pathways and stimulate muscle protein synthesis similarly in young, healthy individuals, despite differences in bioavailability.¹⁹ That suggests that calcium HMB is just as potent (or non-potent) as free HMB.

Dosage and Timing of HMB

How much HMB should you take, and when should you take it?

Dosage

The most common HMB dosage in studies is 3 grams per day. That amount is not scientifically proven to be the optimal dose, but studies using 6 grams instead haven’t found a dose-dependent effect where more is better.²⁰ ²¹

Timing

If you want o to synchronize any immediate effects that HMB might have with your muscle protein turnover during a workout, a pre-workout supplement might be a good idea.

You absorb free HMB and calcium HMB at different speeds. Therefore, you could take free HMB 30–60 minutes ahead of a workout, but with calcium HMB, you’d have to wait at least an hour between taking the supplement and working out. If you ingest carbs along with the HMB supplement, you probably have to extend that to two hours.²²

How HMB Interacts With Other Supplements

Do you increase the effects of HMB if you take it with other supplements? A couple of studies suggests you do; others don’t.

Creatine

Two studies investigate the effects of combining HMB with creatine during strength training.

The first of these is from 2001.²³ Untrained subjects engaged in strength training for three weeks while using either placebo, HMB, creatine, or the combination of HMB and creatine in a randomized manner.

According to the results, creatine supplementation alone increased strength and muscle mass more effectively than HMB. However, the effects of combining creatine and HMB were additive, suggesting the supplements work through different mechanisms.

In the second study, researchers gave highly trained rugby athletes three grams of HMB or three grams of HMB plus three grams of creatine per day during a six-week- strength-training program.²⁴

This study found that neither creatine nor the combination of HMB and creatine had any effects on strength, power, or endurance.

ATP

Two studies also look at the combination of HMB and adenosine triphosphate (ATP) on muscle mass, strength, and power, in trained individuals.

ATP is your primary energy source when you exercise, and ATP supplements are designed to increase ATP concentrations, supposedly helping you perform better.

The first study is from 2013.²⁵ Trained subjects followed a strength-training program for 12 weeks while receiving 3 grams per day of free-form HMB, 400 mg per day of ATP, or a combination of both. A fourth group acted as controls and received a placebo.

After 12 weeks, both the HMB and the ATP groups showed impressive gains compared to the placebo group, but the group combining the supplements increased their strength and muscle mass even more.

This study is not peer-reviewed and is still, after almost a decade, only available as a poster presentation.

The second study is the Wilson study described earlier in the article, meaning it’s one of the two HMB studies with incredible results that are not accepted in later scientific reviews.²⁶

The poster presentation from 2013 is also from the same team and the same laboratory, casting doubts about those results.

Safety of HMB

HMB supplements are not associated with any adverse effects. Human studies find no side effects of HMB in healthy individuals or people with any medical condition, including cancer and AIDS. Also, combining HMB with other amino acid supplements seems safe as well.²⁷

Animal studies come to the same conclusion. One study gave male and female rats 3.49 and 4.16 grams of HMB per kilogram of body weight per day, respectively, for 90 days.²⁸ It looked for any toxic effects of calcium HMB but found nothing. It didn’t affect the weight, the food intake, the blood work, or the organ weights of the rats. The amount of HMB given to the rats would mean a human using 38–45 grams daily, compared to the typical dosage of 3 grams per day.

A recent study looked at bacterial mutations and chromosomal aberrations in test-tube trials and experiments on living mice, looking for any genotoxic effects of HMB.²⁹ The researchers found no such issues at all.

In Summary

In healthy, untrained individuals, supplementing with HMB might help increase lower body strength a bit, but any positive results on body composition are trivial at best.
Trained athletes do not seem to benefit from using HMB at all. If there are any effects, they are so small that controlled studies can’t find them.
Meta-analyses looking at all the available research can’t find any significant effects of HMB on strength, skeletal muscle mass, or body composition in athletes and trained individuals.
Scientific evidence suggests that HMB has small but significant effects in clinical settings with muscle proteolysis and wasting.
HMB might help you recover from training and improve markers of muscle damage after intense workouts. However, these potential benefits do not translate into more significant gains in muscle mass or strength over time.

In conclusion, we don’t find HMB to be a supplement worth your money for muscle-building purposes. The scientific evidence does not support the use of HMB if you’re looking to build muscle and get stronger.

Want to learn more about dietary supplements? Which ones are worth your money, and which are questionable or useless? Check our StrengthLog’s Supplement Guide, our free guide where I review 26 of the most popular supplements.