What Is HMB (Hydroxymethylbutyrate) Good For, and Does It Have Side Effects?

Hydroxymethylbutyrate (HMB) is a product that occurs naturally in the human body and is also available as a supplement. HMB has gained popularity recently as a potential muscle builder and workout enhancer.

HMB has gained popularity recently as a potential muscle builder and workout enhancer. While evidence is still needed, studies show that it may offer a way to prevent muscle loss and aid in workout recovery.

Hydroxymethylbutyrate (HMB), sometimes written as hydroxymethyl butyrate, is a product that occurs naturally in the human body and is also available as a supplement.

HMB is a compound your body uses to break down an amino acid called leucine. Amino acids are the building blocks of protein. Leucine is an amino acid that helps your body:

• Grow and repair muscle tissue
• Heal injuries
• Make protein
• Make growth hormones
• Regulate blood sugar

Leucine is one of 20 amino acids your body needs to survive. It’s also one of the nine essential amino acids. Your body can’t make these amino acids, so you must get them from food. Foods like eggs, fish, milk, and poultry often provide leucine. Leucine is also available as a supplement.

HMB has multiple effects within the body, including: 

• Decreasing muscle breakdown
• Decreasing high cholesterol
• May reduce the amount of leucine the body needs

There are many different things people take HMB for, but athletes primarily use it to increase muscle mass, strength, and endurance. Other uses include avoiding muscle and weight loss in some populations.

HMB to increase exercise performance and results

Several studies have been done on whether or not HMB can boost exercise performance and results. Multiple studies have shown that HMB provided participants with the following benefits:

• Increasing aerobic performance
• Increasing lean body mass
• Increasing muscle mass
• Increasing physical capacity
• Increasing strength
• Improving recovery
• Reducing muscle damage

Multiple studies have also shown that the participants saw no benefits at all. An overview of the studies seems to show that HMB is most effective in those whose bodies have not already adapted to intense training, such as those who are untrained or those who are trained but are exerting themselves more than usual. The International Society of Sports Nutrition also noted that HMB seems most effective when used for two weeks before heavy training. More studies are needed.

HMB to prevent muscle loss in elderly patients

Up to 13% of people over 60 and 50% of people over 80 experience a condition called sarcopenia. Sarcopenia is a condition where your body gradually loses muscle mass and is thought to be caused by aging. This can lead to difficulty with:

• Balance, leading to falls
• Climbing stairs
• Daily tasks
• Stamina
• Walking

A handful of human studies have been done that show that for elderly patients, HMB can:

• Increase grip strength
• Increase lean tissue mass
• Increase muscle strength
• Increase physical performance
• Preserve muscle mass when the patient is on bed rest
• Reduce body fat

Some studies done on rats show that HMB also helped improve cognitive function for elderly rats. More trials are needed to prove that HMB has benefits for elderly patients.

HMB to prevent cachexia

Also called “wasting syndrome,” cachexia is when a patient loses a significant amount of weight and muscle. This is primarily due to diseases like HIV/AIDS, cancer, heart failure, or chronic obstructive pulmonary disease (COPD). This can lead to problems like decreased strength and fatigue. It can also be difficult for cachexia patients to regain their lost muscle protein.

Multiple studies have been done in labs, rodents, and humans on the effects of HMB on cachexia. In the lab, a handful of studies found that HMB was able to reduce the rate that proteins were destroyed or degraded.

In rats and mice, studies found that HBM was able to:

• Decrease muscle loss in mice with muscular dystrophy
• Decrease protein damage in mice with tumors
• Decrease weight loss in mice with tumors
• Increase grip strength in mice with muscular dystrophy
• Increase protein synthesis in mice with tumors
• Increase the survival time of rats with tumors
• Reduce tumor size in rats
• Slow the loss of body weight and muscle mass in rats with cancer

In humans, studies showed the following results of HMB:

• AIDS: HMB improved body mass, immunity, and strength in AIDS patients
• Cancer: HMB increased body weight and non-fat mass and increased strength in cancer patients
• COPD: HMB increased heart function in patients with COPD
• Chronic heart disease: HMB decreased deaths and improved nutrition, body composition, quality of life, and muscle strength in patients with chronic heart disease
• Critically ill patients: HMB improved the nitrogen balance of critically ill patients
• Hip fracture: HMB accelerated healing time and increased muscle strength in patients with hip fractures
• Knee replacements: HMB prevented strength loss in patients with knee replacements

Some studies, including studies on gastric bypass patients, patients with renal failure, and patients with rheumatoid arthritis, showed no benefits. It’s also important to note that the HMB was included with other supplements in many of the human trials. This makes it difficult to determine how much of the benefits the patients experienced were due to the HMB specifically. More studies are needed.

Currently, no conclusive evidence shows any negative side effects to HMB. There is speculation that excess HMB could lead to an imbalance of other amino acids, particularly the amino acid glutamine. 

Glutamine is an amino acid that your body can make itself, and it’s the amino acid that the human body has the most of. Glutamine is important because it removes excess ammonia from the body and helps your immune system, brain function, and digestion. Some studies have shown that glutamine levels were low in patients undergoing HMB treatment. More studies are needed.

Most manufacturers of HMB supplements recommend 3 grams per day to maintain or improve muscle function and muscle mass. HMB is mainly available in calcium salt tablets, but there is also research into whether a gel is better. Studies offer conflicting results, and more studies are needed.

Currently, there isn’t enough data to say for a fact whether or not HMB is beneficial. Some evidence shows that in certain situations, the potential benefits outweigh the potential side effects. If you have questions or concerns, consult with your doctor.