L-citrulline is one of the three dietary amino acids in the urea cycle, alongside L-arginine and L-Ornithine. Taking L-citrulline increases plasma levels of ornithine and arginine and improves the ammonia recycling process and nitric oxide metabolism. Consequently, it is used in areas where nitric oxide is relevant, namely athletic performance, and vascular health, and erectile dysfunction. There are very few foods that have notable amounts of citrulline, watermelon being a notable exception.