Leucine the Natural Anabolic: Roughly 10% Higher Strength Gains, Improved Body Composition and Fat Loss in Previously Untrained Men Receiving 4g of Supplemental Leucine a Day

These days it is hard to visit any bodybuilding or fitness related website without noticing a blogpost, news-item, article or product recommendation about leucine supplementation. The studies on its (in vitro) effect on mTOR-signaling, AKT-phosphorylation and all the other exotically named indicators of ongoing muscle protein syntheses appear to be ubiquitous. What is yet more important, i.e. the practical outcome of leucine supplementation, is much less talked about and thus I am happy to report the results of a study conducted by researchers at the Carnegie Faculty of Sport and Education of the Leeds Metropolitan University in the United Kingdom (Ispoglou. 2011).

Figure 1: Increase in 5-RM Strength by leucine supplementation in the course of a 12 weeks strength training program (adopted from Ispoglou. 2011).

Unfortunately, yet in view of costs and practicability expectedly, the 26 subjects (age 28.5 ± 8.2 y, body mass index 24.9 ± 4.2 kg/m²) of the 12-week study were previously untrained, but healthy males. This renders the study less significant in terms of the effects of leucine supplementation to professional athletes, of whom I expect to have a higher net protein and thus leucine intake, anyway. On the other hand, this type of study design does excludes effects of additional supplements and isolates the effect of leucine, as one may safely assume that the leucine content of British incarnation a standard westernized diet, which tends to leave out the fish under the fried, greasy breadcrumb coated "fish" in "fish & chips", is pretty low. Thus it does not really come as a surprise that...

the leucine group demonstrated significantly higher gains in total 5-RM strength (sum of 5-RM in eight exercises) and 5-RM strength in five out of the eight exercises (P < .05). The percentage total 5-RM strength gains were 40.8% (± 7.8) and 31.0% (± 4.6) for the leucine and placebo groups respectively. Significant differences did not exist between groups in either total percentage LTM gains or total percentage FM losses (LTM: 2.9% ± 2.5 vs 2.0% ± 2.1, FM: 1.6% ± 15.6 vs 1.1% ± 7.6).

You may now argue that the leucine group did gain more muscle mass and lose more fat - yeah that is right, but this difference is way lower than the standard-deviation (i.e. the statistical measure of the mean intra-group difference between the subjects), which renders these results scientifically "insignificant". It is, nevertheless interesting to see some quantifiable data on what I consider the optimal benefits, i.e. the benefit someone with an initially low leucine intake, can derive from a daily dose of 4g supplemental leucine.