HMB (short for β-Hydroxy β-Methylbutyrate) is a metabolite of the amino acid, leucine. Roughly 5% of dietary leucine gets oxidised into HMB, which is thought to act as an anti-catabolic agent, reducing muscle breakdown (Van Koevering & Nissen, 1992).
Tests have been looking at leucine on its own and after a period of time, but it took a large dosage on a calorie restricted diet to see additional anti-catabolic improvements. It has since been suggested this is due to enough HMB being metabolised and reaching a level to help prevent muscle breakdown as opposed to the leucine on its own, which is known to benefit muscle protein synthesis. Further research has looked at the use of HMB as a dietary supplement on its own, with positive results.
What Are The Benefits?
Research has shown that HMB supplementation improves lean muscle mass, strength and body composition. However, some of this research is confusing and conflicting, making it hard to decipher the truth from the theory.
The main process in which HMB works is to prevent muscle breakdown, which has been seen from decreases in blood markers that are prevalent when muscle damage occurs (Nissen et al., 1996). Since then, HMB became a popular topic of research in mainly untrained or resistance-trained participants (Rowlands & Thomson, 2009), showing signs of improvements in strength, size and body composition. It is widely unknown the exact mechanisms which cause each of these outcomes, but have been linked to each in animal models and proposed biochemistry as well as indirect measures in human trials (Thomson et al., 2009).
While the research has pointed to many different measures. The fact that HMB is meant to reduce the effects of muscle damage and prevent muscle breakdown points to an increased level of recovery in a faster time so you can train harder, sooner. This will have the benefit of increasing muscle size and strength which will, in turn, increase your metabolism when moving, therefore increasing your fat burning potential.
Critically looking at some of the studies on well-trained athletes as well as those that also didn’t find an effect of HMB, the training and nutritional plan and requirements may not have been sufficiently stimulating between groups to utilise the main effects of the supplement (Rowlands & Thomas, 2009). This has also been suggested as a limitation in a study on elite rugby players with another limitation being the lack of knowledge of the direct human mechanism and the ideal subject characteristics for an effect to take place (O’Connor & Crowe, 2003).
While a few different dosages have been trialled, 3g per day seems to have the best benefit (additional dosages do not seem to have any additional benefits) and can be used alongside other supplements to further increase performance. Creatine monohydrate is a common supplement to use with HMB as they can have an additive effect when combined.
Who Is HMB Suitable For?
HMB has been found to have no known side effects at all and it is not on the WADA banned substance list, so there is no one who should avoid this supplementation. The greatest benefits of HMB from the research seems to be in the first 1-2 months of training from novice lifters (Rowlands & Thomson, 2009).
However, looking at the mechanisms and some of the key ways it can affect the human body, I would recommend it to anyone who is increasing training load to give your body a recovery boost and prevent muscle wastage, especially when on a calorie-controlled diet, or for vegetarians who struggle to get the leucine content in their diet.
While the research is still trying to work out the process that can cause promising levels of adaptation, it seems clear that in novel forms of training HMB has a positive effect. This will be during periods of high overload or during calorie restriction to aid improvements.
Van Koevering M, Nissen S Oxidation of leucine and alpha-ketoisocaproate to beta-hydroxy-beta-methylbutyrate in vivo . Am J Physiol. (1992)
Thomson, J., Watson, P. & Rowlands, D Effects of nine weeks of b-hydroxy-bmethylbutyrate supplementation on strength and body composition in resistance trained men. Journal of Strength and Conditioning Research. (2009)
Rowlands, D. & Thomson, J. Effects of b-hydroxy-b-methylbutyrate supplementation during resistance training on strength, body composition, and muscle damage in trained and untrained young men: a meta-analysis. Journal of Strength and Conditioning Research. (2009)
O’Connor, D. & Crowe, M. Effects of b-hydroxy-b-methylbutyrate and creatine monohydrate supplementation on the aerobic and anaerobic capacity of highly trained athletes. J Sports Med Phys Fitness. (2003)
Nissen, S. et al., Effect of leucine metabolite b-hydroxy-b-methylbutyrate on muscle metabolism during resistance-exercise training. J Appl. Physiology. (1996)