Aspartic acid is a nonessential, natural amino acid widely distributed in proteins that plays a major role in the energy cycle of the body. It helps transport potassium and magnesium into cells and is found in high concentrations in the brain. Aspartic acid rids the body of excess ammonia and, in combination with other amino acids, absorbs and removes still other toxins from the blood stream. Low levels of this amino acid are thought to contribute to sluggishness and possibly chronic fatigue syndrome. Consequently, it is often recommended for alleviating fatigue and increasing stamina and endurance. When chemically combined with phenylalanine, it forms aspartame, a synthetic sweetener added to diet drinks and foods and found under the trade names Nutrasweet and Equal.