Beta-hydroxy beta-methylbutyrate, or HMB, is touted as a muscle-building supplement that many, according to anecdotal stories at least, athletes find advantageous.
Besides being used as a muscle-building supplement for fitness enthusiasts, HMB has been used to aid in the healing process of people suffering from wasting due to cancer, HIV/AIDS and trauma patients recovering from severe injury. It has also been used in animals to increase disease resistance and size of livestock.
HMB is a metabolite of the amino acid leucine and plays a part in protein synthesis - the process by which cells build proteins. Protein synthesis is an ongoing process and your muscles are always in flux as old proteins are being broken down while new ones are being made to replace them.
Strenuous exercise stimulates protein breakdown (also known as proteolysis) in muscles, and therefore stimulates protein synthesis as well. In order to build muscle, however, the rate at which muscle is built has to be greater than the rate at which it degrades. This is where HMB comes in.
HMB proponents say that it limits the amount of protein which is degraded during intense exercise, leading to an increase in muscle mass as new proteins are being built. This seems logical but there is some contention as to what HMB actually does as a training supplement.
Firstly, it appears that HMB is only effective during periods in which the body is exposed to severe trauma or stress . Therefore, HMB as a muscle-building supplement is only successful when used in conjunction with arduous exercise or heavy weightlifting.
The results of studies of HMB are mixed - some say that HMB has an effect on increasing muscle strength and weight; others find no discernible effect . One study found that HMB supplementation 'reduced signs and symptoms of exercise-induced muscle damage in non-resistance trained males following a single bout of eccentrically biased resistance exercise' .
Another study states 'that HMB may play an important role in reducing protein degradation and/or increasing recovery of damaged muscle cells. These actions could be advantageous to all individuals participating in exercise programs and improve the lives of many by overcoming weakness or frailty' . A third found that 'HMB may increase upper body strength and minimize muscle damage when combined with an exercise program' .
Finally, one study found that dietary supplementation of the leucine metabolite beta-hydroxy-beta-methylbutyrate (3 g/day) in people undertaking intensive resistance training exercise, resulted in an increased deposition of fat-free mass and an accompanying increase in strength. Muscle proteolysis was also decreased with HMB .
On the other side of the aisle, a study in which one group of collegiate football players were given HMB and a control group was given a placebo, 'no significant differences between the groups were seen. Results suggest that short duration HMB supplementation does not provide any ergogenic benefit in collegiate football players during preseason training camp' .
A similar study, again using collegiate football players, found similar results. This study found that 'there were no significant changes in muscular strength, including bench press, squats, and power cleans, among the subjects. There were also no significant changes in body composition, including body fat and body weight. They concluded that very little clinical evidence exists for supplementing HMB in athletic populations .
There also seems to be a link between average, untrained people and the positive effects of HMB. That is to say that untrained athletes seem to get better results with HMB than highly-trained athletes .
There have been no discernible side effects found with HMB supplementation to date. Even those studies that do not recommend it as a training supplement find no apparent side effects .
Since it is a new supplement however, it is recommended that women pregnant or nursing or those with severe kidney or liver disease refrain from using HMB without consulting a doctor. As with many modern supplements on the market, it's worth bearing in mind that no long term studies have been completed to measure the safety of HMB.
There is a lot of debate as to how effective HMB is as a muscle-building supplement. Some studies say that is has significant effects, yet others state that is has no noticeable effect at all.
For those who can afford this relatively expensive supplement, it may be best reserved for newcomers to resistance training, or during the first few weeks of a new training programme. At best you should expect only modest additional gains to proper diet and training alone.