Three major companies (Twinlab, MetRx, and EAS) currently market the nutritional supplement HMB, or beta-hydroxy beta-methylbutyrate (http://www.sports-nutrition.org/mesomorphosis/3022645.html). HMB has been highly acclaimed since itís recent market debut by EAS (http://www.eas.com/research/hmb/mindex.html). Many critics have compared it to the wonder-product Creatine Monohydrate. Such a comparison undoubtedly harbors both positive and negative aspects. But nevertheless, HMB products continue to thrive in nutritional stores worldwide.
I. What is HMB?
"HMB (hydroxy-methylbutraye) is a metabolite of the amino acid Leucine and is produced naturally by the human body. HMB is produced from a metabolite of leucine, called ketoisocaproate (KIC), by the enzyme KIC-dioxygenase. And, at least in the pig, HMB is produced exclusively from leucine"(Nissen p.2095).
II. How does HMB work?
Steven Nissen and his colleagues have performed the only study to date of HMB on humans. The researchers agree that the mechanism by which HMB impacts muscle proteolysis and function is not currently known. Nevertheless there are a number of postulations. "The high substrate concentration required by the dioxygenase enzyme compared with the liver concentration of KIC suggests that HMB production in the body may be a first-order reaction controlled by enzyme and KIC concentrations. It has been calculated that, under normal conditions, about 5% of leucine oxidation proceeds via this pathway. Therefore, if humans are assumed to have enzyme actions similar to those seen in pigs, a 70-kg human would produce from .2 to .4 g HMB/day depending on the level of dietary leucine. At leucine intakes of 20-50 g/day (which are used therapeutically), the concentrations of leucine and KIC in the liver increase and could result in HMB production reaching gram quantities per day"(Nissen p.2095). Some studies involving HMB supplementation to the diet of steers and pigs have been shown to improve caracass quality. Based on these findings, it has been hypothesized that supplementing the diet with HMB may inhibit protein degradation during periods of increased proteolysis such as resistance training.
III. What are the Claims?
The three companies that currently market the product recommend 1.5-3.0 grams of HMB/day as a dietary supplement. Although the science behind the productís effectiveness is rather unclear, all three companies show few distinctions between dosages and manufacturing. Most people who have noticed the product often see HMB advertised as a protein breakdown suppressor. Researchers claim that such an advantage actually enhances the gains in muscle strength and lean mass associated with resistance training. Companies who promote the product claim that humans neither produce enough HMB in their bodies, nor do they eat such HMB-containing foods (e.g. catfish and grapefruit) regularly enough to provide the full benefits of HMB. Researchers claim that when we input extra amounts of HMB into our bodies the metabolite acts as a performance enhancer for such activities as weight lifting and sprinting. In effect, companies claim that HMB boosts strength levels, enhances gains in muscle size and strength, and prevents post-workout muscle tissue breakdown. The marketing companies do not make exactly clear how the product works, but they have formulated a few widely accepted ideas which are seen on the advertisement postings in many nutritional stores. Many of them believe that excess amounts of HMB in the body cause an interference with the bodyís natural process of protein breakdown (particularly after a workout). In doing so, HMB allows athletes to retain more protein in their system, resulting in increased energy levels and faster recovery. Of course the companies claim that this product is only beneficial to those who workout in addition to HMB supplementation. Internet advertisements claim that there are countless experiments involving placebos and HMB supplements, which have resulted in substantial performance increases in the many groups of athletes who have taken HMB along with their training regimen.
IV. First Impressions
In my search for information about HMB, I found that most of the claims and information were fairly similar. Since so few companies actually market the product such a common thread is expected. I did find it interesting however that none of the companies recognized any side effects whatsoever throughout all of the experiments and research of the product. This concern has become all too familiar in the recent explosion of nutritional products. Perhaps there is more to be discovered about HMB in cases of long-term usage.
V. What is the Research Evidence?
As I began searching for information on the 'countless studies' involving HMB and its connection to athletic performance, I noticed that it was rather difficult to pinpoint any studies involving humans. And even the studies on animals were limited. This is more than likely due to the fact that HMB is a relatively new product on the market. The one primary research report on humans that I found was a very popular one. I noticed that many of the review papers used it is a reference tool. The study was conducted by Steven Nissen, and a number of his colleagues in November 1996.
A. Nissen Study
In the second study Nissen took another random sample of 28 individuals and divided them randomly into two levels of HMB supplementation (0 and 3 g HMB/day). In both groups, the subjects lifted weights for 2-3 hours and 6 days per week for 7 weeks.
B. Papet Study (Papet, et al. June 1997)
C. Van Koevering Study (Van Koevering, et al. August 1994)
VI. Primary Research Wrap-Up
Due to the fact that a limited number of HMB studies have been performed on humans, we must also consider the results of the tests on animals. Perhaps there is a connection between the noted improvements in the two animal tests and those of humans. This data alone, however, is insufficient. Since HMB is a relatively new product, one must take into consideration the possible side effects or other negative aspects of upsetting a natural balance within the body. There were a few review papers that I found expressing both skepticism and praise of HMB as a dietary supplement.
VII. Review Paper Reactions to HMB Studies/Claims
VIII. Are There Any Confounding Variables in the HMB Study on Humans?
Since there is only one concrete study of the effects of HMB on the athletic performance of human beings, confounding variables are of great importance. If a lurking variable were to skew the results of Nissen's study then the base of support for the companies claims would be unsubstantiated. Therefore I proceeded with caution when formulating a final opinion on the effectiveness of HMB. In reading through Kreider's review paper on Nissen's study, I found a possible lurking variable. Kreider realized that in the one study that reported significant gains in fat-free mass in resistance-trained athletes, "HMB was added to a popular carbohydrate/protein vitamin/mineral fortified meal replacement supplement"(Kreider p.107). Therefore it is unclear whether HMB supplementation and/or some other combination of nutrients was responsible for the gains in fat-free mass observed. This is undoubtedly an important consideration in reviewing the study, which has the potential to be the basis for a concerned consumer's opinion.
IX. Final Impression
After reviewing the sparse and conflicting information regarding the effectiveness, I came to the conclusion that there is simply not enough concrete evidence to support the claim that HMB promotes the growth of lean muscle mass and reduces proteolysis. This is not to say that the product is unsafe, especially since, to my knowledge, there have been no contradicting studies or documented side effects from the product. I did, however, discover a few of the underhanded marketing techniques used by the companies. They claimed that there were countless research studies, which proved HMB's validity as an effective nutritional supplement. This was not nearly the case. The simple fact that a resourceful university library produced only one study involving HMB on humans, is evidence enough to argue that the promoters are over-generalizing the facts behind the study of the product. The companies backing HMB have made a number of claims that their product is beneficial to resistance-trained athletes. So far there have been no concrete indications suggesting otherwise.
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