A good anti-catabolic agent—–HMB

HMB (short for β-Hydroxy β-Methylbutyrate) is a metabolite of the amino acid leucine that, along with KIC (α keto-isocaproate) and isovaleryl-CoA, mediate the effects of leucine. Approximately 5% of dietary leucine is oxidized into HMB, and HMB appears to be the main metabolite of leucine that more effectively prevents the breakdown of muscle protein.

When compared to leucine, HMB appears to be significantly more potent on a gram per gram basis at attenuating the rate of muscle protein breakdown but is less effective than leucine at inducing muscle protein synthesis. Due to this, HMB is marketed as an anti-catabolic agent (purposed to reduce the rate of muscle breakdown) rather than an anabolic agent (purposed to increase muscle mass).

Human trials don’t normally tend to be structured to properly assess the effects of HMB, as most of the studies are a standard diet paired with an exercise regimen investigating the role of HMB in promoting muscle protein synthesis (of which it is similar to leucine in the sense that there are positive results, but quite unreliably so); the limited evidence that assesses HMB during periods of muscle loss are either underpowered or not in athletes.

HMB, currently, appears to be a pretty interesting supplement for the purpose of reducing muscle wasting during periods where muscle atrophy is accelerated (cachexia, AIDS, bedrest) and should theoretically work in athletes on a calorie restricted diet but is not fully established for this role yet (which is a notable issue, since glutamine has a large dichotomy between clinical and healthy populations).

HMB is used for increasing the benefits from weight training and exercise; and for treating diseases of the heart and blood vessels (cardiovascular disease), high cholesterol, and high blood pressure. In combination with the amino acids arginine and glutamine, HMB is also used for treating weight loss, weakness, and diarrhea in people with AIDS (AIDS-related wasting).

One of the earliest studies conducted on HMB occurred in 2000. The study, published in the research journal Nutrition, recruited a group of 36 men and women, ages 20-40, and gave half the group 3g/day HMB while the other half received a placebo. Following a 4 week resistance training program, the HMB group increased upper body strength and fat free mass compared to the placebo group.

Another double-blind, placebo-controlled study, also published in Nutrition, investigated the effects of creatine, HMB, and a combination of the two compounds on individuals for a period of 3 weeks. Overall, all 3 groups gained strength and there was also a reduction in creatine phosphokinase (marker of muscle cell damage) compared to the placebo group.Researchers concluded both HMB and creatine induce strength gains, but via different physiological mechanisms.

HMB supplements are available in both tablet and powder forms. Some supplements use calcium-HMB for easier absorption by the body, while others use a free-acid form of HMB. Calcium-HMB is the much less costly version of this compound.

Supplementation of HMB tends to be in the dosage range of 1-3g daily for the purpose of reducing muscle mass losses over time (anti-catabolic). As HMB is said to be 20-fold more potent than leucine for this purpose, it is seen as equivalent to 20-60g of leucine supplementation.

For the purpose of muscle protein synthesis, HMB and leucine are fairly equivalent if not the latter (leucine) being more potent on a gram basis. HMB is not advised for inducing muscle protein synthesis since leucine is likely more effective as well as cheaper.