Aspartic acid, readily available in protein foods, is very active in many body processes, including the formation of ammonia and urea and their disposal from the body. It is found in high levels throughout the human body, especially in the brain, where it performs an excitatory function. Aspartic acid has been found in increased levels in people with epilepsy and in decreased amounts in some cases of depression. Aspartic acid also can help form the ribonucleotides that assist production of DNA and RNA and aids energy production from carbohydrate metabolism.
Aspartic acid can help protect the liver from some drug toxicity and the body from radiation; it may also increase resistance to fatigue. Aspartic acid is employed to form mineral salts, such as potassium, calcium, or magnesium aspartate. Since aspartates are easily absorbed, they can actively transport these minerals across the intestinal lining into the blood and cells where they can be used for their particular functions, such as energy production or bone metabolism.
Asparagine, formed from aspartic acid, aids the metabolic function of the cells of the brain and nervous system by releasing energy as it reverts back to aspartic acid.
Clinically, aspartic acid may be used to treat fatigue or depression. Its effect on the thymus gland lets it be used as a mild immunostimulant. A current popular use is in the sweetener, aspartame (see Chapter 11, Environmental Aspects of Nutrition), which is a combination of aspartic acid and phenylalanine. Aspartic acid is basically nontoxic.