|Dr. Jekyll & Mr. Hyde - Is HMB have another janus-faced supplement ?|
Some details on the experimental protocol
The scientists started out with a total of 61 animals that were initially divided into three groups. The animals in the groups were either sedentary, had to exercise for 1h (endurance) 3x/week or followed the same exercise protocol, yet with an addition of 0.5g/kg body of HMB in their diets (the human equivalent dose would be 6-7g/day depending on your body weight).
After a four-week run-in phase there was an additional differentiation for the non-sedentary rats which leaves us with the following four groups:
- ALT: ad libitum fed fed + exercise (1h/d for 3d/wk)
- ALTH: same as ALT + HMB (0.5 g/kg BW/day)
- C: 30% energy restriction + exercise (6h/d for 6d/wk)
- CH: same as C + HMB (0.5 g/kg BW/day)
|Table 1: Ingredients of the diets in the four groups.(Parks. 2013)|
Without giving away too much, I can say that the results were not what you'd probably expect
As you can see in figure 1 part of the results are probably not like most people would expect them to be. While the provision of HMB did work its body recompositioning magic in the rodents that could eat as much as they wanted, it compromised the fat loss and increased the total loss of lean body mass in the rodents that were fed the -30% calorically reduced diet.
|Figure 1: Changes in body composition (left), strength & motor function (right). Note that the effects of HMB depend on the energy content of the baseline diet (Park. 2013)|
|Figure 2: Dr. Jeckyll & Mr. Hyde effects of HMB ingestion during a caloric deficit; gastrocnemius CSA on the left, mTOR and p-AKT levels on the right of the central illustration (based on data from Park. 2013)|
Devils advocate: "Why are the potential downsides not mentioned in the abstract?"
In view of the previously described observations, and the undeniable negative effect of HMB in the overtraining + undereating scenario (CH group), I'd like to disagree with the researchers' imho unwarranted hypothesis that
"[...]net protein synthesis may have been greater with HMB during the catabolic condition due to its greater inhibitory effect on the protein degradation pathway" (Park. 2013)It's a neat ad-hoc hypothesis which is yet not, as the context would suggest, "based on [the scientists'] mRNA data", of which I already told you that both AKT and mTOR are lower in the gastrocnemius and soleus (fast & slow twitch) muscle of the HMB rodents in the CH group. And, this is certainly more important it stands in contrast with the overall effects on lean mass - so if anything, this argument could be made for the gastrocnemius, only. The overall net protein synthesis on the other hand, must clearly have been lower and not as Park et al. suggest higher.
HMB improves body composition and sensorimotor function during normal training", but follow that up with an at least questionable statement about how it also "attenuates muscle mass [...] loss during catabolic conditions" (Park. 2013) is odd.
Playing advocatus diaboli (lat. for "devil's advocate), I could argue this was a concession to Metabolic Technologies, Inc. who do not just happen to have the exclusive license for the patent on HMB (learn more), but are also among the sponsors of the study.
|The beneficial effects of HMB that have been observed in previous human studies never dealt with a scenario like the one in the study at hand. The training load was usually low or easily manageable and the food intake sufficient just as it was in a recent study that was conducted on elite canoeists (read more)|
Based on the study at hand, of which we will obviously have to see, whether its results can be replicated in human beings, it does therefore not appear advisable to use HMB on a highly restrictive diet, if you do not happen to compete in weight classes and are more concerned about a loss of strength than negative effects a highly restrictive dietary regimen could have on your body composition.
It should go without saying, though that the overtraining + undereating approach to cutting body fat is a no-go with or without HMB, so in essence, all you need to do is to avoid following this path towards misery and you don't have to care much about the relevance of the results of this study.
- Park BS, Henning PC, Grant SC, Lee WJ, Lee SR, Arjmandi BH, Kim JS. HMB attenuates muscle loss during sustained energy deficit induced by calorie restriction and endurance exercise. Metabolism. 2013 Jul 19. doi:pii: S0026-0495(13)00186-8.