L-arginine has recently emerged as the superstar amino acid, displacing such previous favorites as glutamine and leucine. That’s particularly interesting because L-arginine isn’t even considered an essential amino acid, meaning one that must be provided in food. Like glutamine, it’s a conditionally essential amino: one that’s required in greater amounts during times of growth and stress.
Although arginine has been largely associated with promoting growth hormone release, its present popularity stems from its position as the immediate dietary precursor of nitric oxide. NO is both a gas and a free radical that is short-lived in the body but that performs myriad vital functions.
A recent study featured the Zucker rat, a genetically altered animal that exhibits the same effects of type 2 diabetes and obesity as humans’elevated blood glucose; elevated blood lipids, such as cholesterol and triglycerides; elevated resting insulin levels; and dysfunction of the lining of blood vessels that leads to atherosclerosis, high blood pressure and cardiovascular disease.1 Researchers gave the fat, diabetic rats arginine because of the relationship between NO and fat metabolism. NO increases the expression of a chemical that leads to increased activity of mitochondria in cells. Fat is oxidized in the mitochondria. When the genes of rats are manipulated so that they don’t produce NO, they always show higher bodyfat levels than ordinary rats, even though they eat the same amount of food. Inhibiting NO in rats also increases blood levels of triglyceride, or fat.
Since NO stimulates fat oxidation in fat cells, the experimenters hypothesized that giving the Zucker diabetic rats, as they’re known, arginine would increase NO production and possibly decrease bodyfat levels. Some rats got arginine as 1.25 percent of their overall caloric intake in drinking water for 10 weeks. Other rats got no additional arginine.
In the arginine rats, blood arginine levels rose 261 percent, and NO was elevated by 70 percent. The bodyweights of the arginine-treated rats were 6, 10 and 16 percent lower than the control rats at weeks four, seven and 10. Abdominal fat dropped by 45 percent. Serum levels of glucose dropped 25 percent; triglycerides dropped 23 percent; free fatty acids dropped 27 percent; homocysteine dropped 26 percent. By the 10th week of the study, NO production had increased in the arginine-treated rats by 71 to 85 percent, fat oxidation had increased 24 percent, and glucose oxidation was boosted by 34 to 36 percent. The genes related to fat oxidation increased considerably in the arginine rats, with two animals showing increases as high as 789 and 500 percent.
The arginine treatment didn’t increase insulin or growth hormone release. No side effects occurred, nor was the uptake or metabolism of any other amino acid adversely affected. Arginine did, however, increase the weight of the rats’ skeletal muscles, heart and brain. Other animal studies also show that arginine benefits protein synthesis, but it doesn’t affect muscle protein breakdown, or catabolism.
One of the substances increased by arginine reduces the availability of malonyl coenzyme-A, which is a primary inhibitor of fat oxidation in the mitochondria. That substance increases in the presence of carbohydrates, which explains why eating carbs just before training blunts fat burning during the workout. Specifically, malonyl coenzyme-A blocks the enzyme that works with L-carnitine in shuttling fat into the mitochondria for oxidation purposes.
Another recent study showed that dietary arginine lowered levels of C-reactive protein in the body.2 CRP is a general measure of inflammation in the body, and inflammation is the cornerstone of most serious diseases, including cancer and cardiovascular disease. Most supplements, even potent antioxidants such as vitamins C and E, have little or no effect on CRP. The effect on CRP may explain why eating nuts and fish protects the cardiovascular system; both foods are rich sources of arginine. Eating 3.6 ounces, or 100 grams, of walnuts provides 2.5 grams of arginine.
Arginine is thought to lower CRP levels through several possible mechanisms. Its antioxidant activity is independent of its role as a NO precursor, since NO itself is an oxidant. Arginine also positively affects immune function, which helps to reduce the inflammation characteristic of high CRP levels. IM
1 Fu, W.J., et al. (2005). Dietary L-arginine supplementation reduces fat mass in Zucker diabetic fatty rats. J. Nutr. 135: 714-721.
2 Wells, B.J., et al. (2005). Association between dietary arginine and C-reactive protein. Nutrition. 21:125-30.