HMB: What does the evidence say for Athletic Performance?

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• Can you explain the MTOR pathway, what's its significance and how does it work with Leucine and supposedly HMB?
  • That's a good question. Especially in early 2000's lots of studies of protein ingestion can activate protein synthesis. Eating protein promotes synthesis, but issues proving or showing it. Eating protein activates PI3K-Akt-mTORC1 pathway. mTORC1 has been know for years as a protein promoting synthesis. In muscle we are synthesizing protein all the time. This pathway can increase activity or decrease activity; can go up or down throughout the day depending on things you do, for example, eating protein promotes this pathway. Resistance exercise stimulates this pathway. Combine dietary and muscle contraction effect and see that they both stimulate protein synthesis. More protein activates pathway more, so does proper loading in resistance exercise. Now we now that there is a protein, Sestrin2, that is a negative regulator of mTORC1 pathway. Leucine binds Sestrin2 protein and releases inhibition of mTORC1 pathway. Every time we eat protein and leucine goes up, it is transported to your muscle. Benefits of leucine inside the muscle is going to release inhibition and increase protein synthesis. Problem with HMB is that we have data that it activates mTORC but we don't know the mechanism. We don't have many labs investigating this, which is the issue. More labs will lead to faster discovery.
• Are there more than 2 papers in humans that show increase in lean muscle mass?
  • Yes - especially the early 2000's studies. There are some positive effects of HMB. However, they demonstrate the difference between the HMB and placebo group as only being 1-2kg more difference compared to the 5kg gain study
• What is the recommended age at which this supplement could be administered?
  • Right now the product is marketed for all ages. Older adults marketed to help decrease lean muscle mass. Clinical used as immune regulator. Marketing is to prevent sarcopenia. Unclear if it is effective. Most reviews for older populations are low quality and those that show results they are negative.
• For HMB studies in humans assessing lean mass increase, do you think that genetics should be taken in account?
  • I think so yes. Especially in the last 5 years it has been shown that the response to resistance training can be variable. Most people are in the middle, they respond at some level. In the future we are going to need to know if they are high or low responders.