HMB, or beta-hydroxy-beta-methylbutyrate, is a popular bodybuilding supplement that should be included in any supplement catalog , bacuse it can help you gain and maintain more lean mass. It does this by helping prevent the protein breakdown normally associated with training and other stressors. Less muscle loss can mean more net muscle over the long haul.
Not surprisingly, these effects have been enough to spur scientific interest in HMB and especially into just how it might spare protein in the body.
Let’s take a look at what studies have found out about the mechanisms of HMB’s actions on your muscles.
What Is HMB?
Leucine is a branched-chain amino acid that was found in the 1980s to boost the rate of protein synthesis in mammals and also, at least under certain circumstances, to slow down proteolysis — muscle breakdown. However, the proteolysis effect was found to require more leucine than did the increase in synthesis rate. Researchers speculated, then, that proteolysis suppression was due mainly to one or more metabolites of leucine rather than to the amino itself.
Later studies confirmed that one of those metabolites, HMB, does show proteolysis-suppressing tendencies. A 2008 literature review from researchers at the University of Illinois found that, while HMB did not produce lean gains for all users, most of those undergoing heavy muscle trauma did experience gains when using HMB.
These results were interesting, but the exact mechanism of how HMB dampens proteolysis is not fully understood. There are some theories, though.
How Does It Work?
In that same 2008 review, the researchers ran down two leading theories for HMB’s anti-catabolic actions. They are:
Cholesterol Synthesis Hypothesis
This theory states that damaged cells might have a compromised ability to produce new cholesterol, which is vital for proper cell function and the repair of various cellular structures. This may be especially true for muscle cells damaged or traumatized by heavy weight training. The limiting factor in the production of new cholesterol in muscle cells is the formation of HMG co-enzyme A, or HMG-CoA, which forms the cholesterol precursor mevalonic acid. As it turns out, the majority of HMB available to your muscles is converted into HMG-CoA, so having more HMB available during times of cell repair may limit the amount of protein turnover. Less protein turnover should lead to more muscle mass over time.
Ubiquitin-Proteasome Proteolysis Pathway Effects
There are three major pathways, or mechanisms, through which proteolysis occurs: lysosomal, calcium activated calpain, and Ub-pathways — ubiquitin-proteasome pathways. Of these, the Ub-pathways have been shown to be involved in the breakdown of muscle associated with wasting diseases like cancer, limb immobilization, starvation, and extreme exercise applications. As it turns out, studies have demonstrated these same populations to be the ones most positively affected by HMB supplementation, which provides at least indirect evidence that HMB may interfere with the UB-pathways responsible for proteolysis.
While more detailed chemical studies focused directly on uncovering the proteolysis-limiting mechanisms of HMB usage — rather than its gross effects on protein turnover — are needed to give a definitive answer to how it works, these two theories provide some promising leads and food for thought.
Should You Use HMB?
If you train hard enough on a consistent basis to cause significant muscle damage, scientific evidence shows that HMB has the potential to help you limit your rate of protein breakdown and build new mass over the long haul. If, on the other hand, you are very advanced and train in more of a maintenance mode, then HMB may not yield significant results.
If you do decide to try HMB, make sure that your doctor knows what you’re planning and checks you out first to make sure that the supplement won’t cause you any trouble. After all, while bigger muscles are great, nothing is as important as your health!
