7.5g Additional Leucine per Day Alone Do Not Seem To Do the Trick. No Effect on Glycemic Control or Body Composition in 6 Month Trial

The beneficial effects of leucine on the protein synthesis signaling cascade have been a recurring topic in the past months. A recent study from the Top Institute Food and Nutrition in the Netherlands (Leenders. 2011), which is going to be published in the upcoming issue of the Journal of Nutrition, took up on findings from rodent studies, which showed distinct effects of leucine supplementation on both insulin secretion and body composition and investigated the effect of 6 month supplementation with 3 x 2.5g supplemental leucine (with meals) on body composition, muscle fiber characteristics, muscle strength, glucose homeostasis, and basal plasma amino acid and lipid concentrations in a group of 60 elderly males with type 2 diabetes (age, 71 ± 1 y; BMI, 27.3 ± 0.4 kg/m(2)).

Figure 1: Chemical structure of leucine.

Other than they had expected, Leenders et al. did not find any significant influence (positive or negative) of leucine supplementation on the parameters they evaluated:

Lean tissue mass did not change or differ between groups and at 0, 3, and 6 mo were 61.9 ± 1.1, 62.2 ± 1.1, and 62.0 ± 1.0 kg, respectively, in the leucine group and 62.2 ± 1.3, 62.2 ± 1.3, and 62.2 ± 1.3 kg in the placebo group. There also were no changes in body fat percentage, muscle strength, and muscle fiber type characteristics. Blood glycosylated hemoglobin did not change or differ between groups and was 7.1 ± 0.1% in the leucine group and 7.2 ± 0.2% in the placebo group. Consistent with this, oral glucose insulin sensitivity and plasma lipid concentrations did not change or differ between groups.

These results, derived from a study in diabetic patients and via supplementation of only one of the three BCAAs (leucine, isoleucine, valin) stands in contrast to findings of Zhang et al. (Zhang. 2011) who showed only very recently, that supplementation with only 5g of BCAAs

[...]temporarily increased plasma insulin levels and affected plasma concentrations of FFAs, but had almost no effect on glucose or urea nitrogen. 

Against the background that the Zhang study was conducted with healthy, normo-insulinemic subjects, it is most likely that the absence of measurable effects on glucose measurements Leenders et al. describe, must be attributed to the fundamental inability of the type II diabetics' pancreases to respond to the leucine-induced stimulus. A possible synergy (beyond the action of leucine, alone) of leucine, isoleucine and valine, the three BCAAs administered in the Zhang study would yet be another point to consider, before discarding leucine and/or BCAAs as a treatment strategy for two of the major symptoms of the metabolic syndrome: Obesity (body composition) and diabetes (glucose homeostasis).