Urea is a nitrogenous compound found in the urine and other fluid secretions as a waste product of protein metabolism, when enzymes in fatty acids convert proteins to usable nutrients. Ornithine plays a central role in this process, allowing for the removal of excess nitrogen.
The waste nitrogen in urea comes from ammonia and aspartate, but remains intact in ornithine and is recycled. Some research has studied the effect on the liver of an ornithine-aspartate compound and found it useful in the treatment of cirrhosis.
Ornithine is a popular supplement for athletes and body builders, as depleted nitrogen can lead to loss of muscle and tiredness. Research suggests that ornithine can combat fatigue during exercise by making energy consumption more efficient and stimulating ammonia excretion.
Ornithine is recommended as a nutritional supplement in cases of physical fatigue, or in the case of a protein-deficient diet, particularly for vegans. Most protein sources supply all of the nine essential amino acids, from which ornithine can be metabolised. These are particularly rich in meat, poultry, dairy products, eggs, fish, quinoa and soya beans, but body-builders and athletes use protein quickly as it converts into muscle strength, and so may need supplements.