Hydroxymethylbutyrate (HMB) is a dietary supplement that may help increase muscle strength and exercise performance. It also may help prevent muscle loss and protect the heart. Read below to learn if this supplement is worth the hype.
HMB, also known as β-Hydroxy β-Methylbutyrate or hydroxymethylbutyrate, is a popular bodybuilding supplement. Since the 1990s, athletes and bodybuilders have used HMB to build muscle and improve recovery from exercise .
- May improve exercise performance
- May improve muscle growth
- May prevent muscle loss due to aging and disease
- May lower cholesterol
- Not effective without exercise
- Less effective in trained athletes
HMB is commonly sold as a dietary supplement that is purported to help build muscle mass, improve exercise performance, and improve recovery from exercise.
One systematic review searched through hundreds of HMB-related studies and identified 18 clinical trials that focused on exercise and muscle growth. According to the review, the potential benefits of HMB include :
- Increases in muscle mass
- Increases in strength
- Reduction of muscle damage
- Increases in anaerobic and aerobic performance
- Increases in lean body mass
The International Society of Sports Nutrition (ISSN) has also performed a critical analysis of the scientific literature. The ISSN concluded that HMB :
- Enhances muscle recovery after exercise in trained and untrained individuals
- Works when taken close to a workout
- Is most effective when taken for 2 weeks before heavy exercise
- Increases lean body mass and functionality in the elderly
However, both of these reviews also identified important caveats.
Research suggests that healthy people who do not exercise may see no benefit. This means that non-exercising individuals saw no changes to body composition or exercise performance .
Some studies also show that HMB has little effect on athletes who are already strength-trained. However, trained individuals may see some benefit if the exercise intensity is high enough .
A number of clinical trials have found that supplementation with HMB may help prevent muscle loss caused by various conditions.
For example, age-related muscle loss (also called sarcopenia) affects up to 10% of elderly people. This loss of muscle can lead to weakness and an increased risk of falls .
A systematic review of 7 trials including 287 older adults found that HMB may help preserve muscle in the elderly, while also potentially increasing leg and handgrip strength .
The same review suggests that HMB supplements may prevent muscle loss caused by long periods of bed rest as well .
Based on a systematic review of 13 clinical trials, HMB may help with cachexia in several ways, including :
- Increases lean body mass
- Improves immune status
- Decreases risk of death
- Reduces the feeling of weakness
This review also suggests that HMB may be especially effective for cachexia caused by cancer, steroids, and immobility .
However, there are a few points to note about the studies included in this review.
Many of these studies used other supplements as well, including proteins and amino acids .
Also, these results were not universal – some clinical trials found no benefit compared to placebo .
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of HMB for any of the below-listed uses. Remember to speak with a doctor before taking HMB supplements, and never use them in place of something a doctor recommends or prescribes.
As mentioned previously, HMB may help lower cholesterol. This has led some researchers to explore HMB’s effect on the risk factors for heart disease.
One review concluded that chronic supplementation with HMB with resistance training does not reduce cardiovascular risk factors more than resistance training alone. In other words, the heart-protective effects of HMB may be due to an increase in exercise activity rather than the supplement itself .
However, researchers also state that the amount of clinical research is limited .
The human body is constantly building and breaking down proteins in the muscles. This continual process is how the body maintains its metabolism and energy .
When the body is in a state of building it’s referred to as anabolism. On the other hand, when the body breaks down molecules it’s called catabolism. When anabolism is greater than catabolism there is a net gain in muscle protein [9, 5].
HMB may reduce catabolism by blocking proteasomes (proteins that break down other proteins). This may explain why HMB appears to be especially effective in catabolic states, such as fasting, aging, and disease [11, 10, 12].
HMB also may have anabolic effects, to a lesser extent.
HMB supplements are considered possibly safe.
According to the International Society of Sports Nutrition, long-term use of HMB is safe for young and old patients .
A long-term study in the elderly also did not find any safety concerns after taking HMB for a year .
However, there is some evidence that HMB’s effects on muscle may decrease the availability of certain amino acids .
Research on HMB is not clear-cut. While many clinical trials are promising, a good number of studies have found conflicting results.
For example, one review identified 9 separate studies that show HMB has no effect in trained or untrained people .
It’s also important to note that the majority of studies use the calcium form of HMB (as opposed to the free acid form). Studies sometimes combine HMB with other types of supplements as well.
Supplements generally combine HMB with calcium (Ca) to add chemical stability .
Usually, when we talk about HMB, we are actually referring to the HMB-Ca form. This is because, for a while, HMB-Ca was the only form of HMB available .
However, HMB in its free acid form (HMB-FA) has recently become commercially available and there are potentially important differences.
- HMB-FA may work faster than HMB-Ca. In the study, HMB-FA reached peak blood levels in 30 minutes vs HMB-Ca which takes about 120 minutes.
- HMB-FA may reach higher levels in the blood. Peak blood levels of HMB-FA were near twice the amount seen with HMB-Ca.
- The half-life of HMB-FA may be slightly longer. HMB-FA half-life appears to be 3 hours while HMB-Ca is 2.5 hours.
- The plasma clearance of HMB-FA may be greater than HMB-CA. Plasma clearance may indicate how fast the body is using up HMB, which implies that the body may use HMB-FA more quickly and effectively.
However, the vast majority of clinical trials focus on HMB-Ca. The safety and effectiveness of HMB-FA are not as clear.
Clear Muscle is a popular supplement marketed as a muscle and strength builder.
The active ingredient in Clear Muscle is a compound called BetaTOR, which is a brand name for the free acid form of HMB, also known as HMB-FA.
As mentioned previously with HMB-FA, there is far less research on BetaTOR compared to HMB-Ca. It’s unknown if the two forms have the same effectiveness and safety.
HMB is available as a combination product with creatine, another popular workout supplement.
One randomized placebo-controlled trial of 40 people found that this combination may increase lean body mass and strength more than when either supplement is used alone .
A variety of other HMB combination products are commercially available. This includes combos with BCAA, glutamine, L-Carnitine, and HICA.
Little to no research has been done on these combinations so it’s unclear if there’s a benefit to mixing these supplements.
HMB supplements are available as a capsule or powder.
Conveniently, supplements are typically available as 1 gram (1000 mg) capsules, to be taken 3 times a day.
HMB-Ca should be taken at least 60 minutes before exercise .
HMB-FA should be taken 30-60 minutes before exercise .
Supplements should be taken at least 2 weeks before increasing workout intensity or starting a new training period .
The opinions expressed in this section are solely those of HMB, who may or may not have medical or scientific training. Their reviews do not represent the opinions of SelfHacked. SelfHacked does not endorse any specific product, service, or treatment.
Do not consider user experiences as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare providers because of something you have read on SelfHacked. We understand that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified healthcare provider.
Online reviews of HMB supplements (including all forms and combinations) are generally positive.
Many users report seeing better muscle growth and recovery time after workouts. Some users report seeing benefits after just one week. Others have also seen great results when stacking with other workout supplements.
Negative reviews primarily consist of people who saw little to no benefit. Some users also report experiencing side effects including nausea, stomach pain, and diarrhea, especially from HMB-FA products.
Research suggests that HMB is possibly effective for helping build muscle and improving exercise performance. However, it appears that HMB is most effective for untrained individuals. Trained athletes may still see some benefit, but only during intense exercise. HMB also seems to be ineffective without exercise.