L-Arginine Promotes Muscle

COLLEGE STATION, Texas—According to a recent study published in the Journal of Nutrition, dietary L-arginine supplementation promotes muscle over fat gain and may provide a useful treatment for improving the metabolic profile and reducing body white fat in diet-induced obese rats (2009;139(2):230-37) (DOI:10.3945/jn.108.096362). Male Sprague-Dawley rats were fed for 15 weeks a high-fat (HF) or low-fat (LF) diet beginning at four weeks of age, resulting in 18-percent higher body weight gains and 74-percent higher weights of major white fat pads in HF than in LF fed rats. Starting at 19 weeks of age, rats in each dietary group were supplemented for 12 weeks with 1.51 percent L-arginine-HCl or 2.55 percent L-alanine (isonitrogenous control) (n=8 per treatment) in drinking water and arginine groups were individually pair-fed to alanine controls. Despite similar energy intake, absolute weights of white fat pads increased by 98 percent in control rats over a 12-week period, but only by 35 percent in arginine-supplemented rats. The arginine treatment reduced the relative weights of white fat pads by 30 percent and enhanced those of soleus muscle by 13 percent, extensor digitorum longus muscle by 11 percent, and brown fat by 34 percent compared with control rats. Serum concentrations of insulin, adiponectin, growth hormone, corticosterone, triiodothyronine and thyroxine did not differ between control and arginine-supplemented rats. However, arginine treatment resulted in lower serum concentrations of leptin, glucose, triglycerides, urea, glutamine and branched-chain amino acids, higher serum concentrations of nitric oxide metabolites, and improvement in glucose tolerance.