Both the medical and athletic communities have taken interest in arginine for its potential protein anabolic effects.
However, arginine is heavily metabolized in the splanchnic region, resulting in low bioavailability.
Researchers from France studied the effects of the arginine precursor citrulline.
Citrulline is an amino acid that can be found in watermelons.
It escapes splanchnic uptake and is converted to arginine by the kidney. Therefore, citrulline supplementation might be more effective to raise arginine levels and than arginine supplementation itself.
Earlier research showed protein anabolic effects of citrulline, but mostly in animal models with citrulline deficiency or protein restriction.
The researchers wanted to study the effects of citrulline in healthy subjects. They conducted a cross-over study in which the subjects received both:
- a dose of 0.18 g/kg/d citrulline for 7 days
- a placebo for 7 days
The 7d supplementation of citrulline resulted in 11-fold increase in citrulline and a 2-fold increase in arginine in the blood.
However, they did not find an effect on nitrogen or protein balance. This appears in contrast with earlier findings of the researchers, who found that citrulline increased nitrogen balance in the fed state.
Athletes who are familiar with citrulline probably know it for its potential performance enhancing effects. You might be pleased to hear that as long as you eat, citrulline may also contribute to muscle growth and recovery!