Aspartame is an artificial nonnutritive sweetener synthesized from two amino acids called phenylalanine and aspartic acid. It yields 4 calories per gram during digestion, which is the same amount as sucrose; however, aspartame is 200 times sweeter that sucrose, so only small amounts are used to sweeten foods and beverages.
Digestion in the Lumen
Aspartame is broken apart in the intestinal lumen by digestive enzymes called esterases that release methanol, and peptidases that release aspartic acid and phenylalanine. The three molecules enter the mucosal cells of the intestinal walls and are absorbed into the blood stream.
Digestion in Mucosal Cells
Methanol can be spilt from the aspartame in the lumen, while the aspartic acid and phenylalanine remain bonded together as a molecule called aspartylphenylalanine dipeptide. Intact aspartame molecules can also be absorbed into the mucosal cells. The dipeptides and aspartame molecules are digested by the same enzymes in the mucosal cells, then the individual components are absorbed into the blood.
Amino Acids
The two amino acids found in aspartame are also found in other dietary protein sources. A 2007 review study published in "Critical Reviews in Toxicology" says studies conducted on humans and animals using various dosages of aspartame indicated the absorption of the phenylalanine and aspartic acid had little effect on total plasma amino acid levels, or brain amino acid uptake. Aspartame has no effect on serum lipid or glucose levels, and doesn't change gastrointestinal secretions.
Methanol
Digestion of aspartame produces methanol, which is metabolized first to formaldehyde, then formic acid. According to the study mentioned earlier, consumption of one aspartame sweetened beverage generates 55 mg methanol/L; however, metabolism of fruit juice produces 680 mg/L. Formaldehyde is also found in many foods and produced normally in the body during demethylation reactions of many substances, including food and drugs. Aspartame provides a trivial amount of formaldehyde and formic acid.
References
- "Critical Reviews in Toxicology"; Aspartame: A Safety Evaluation Based on Current Use Levels, Regulations, and Toxicological and Epidemiological Studies; B.A. Magnuson; 2007
- "The American Journal of Clinical Nutrition"; The Aspartame Story: A Model for the Clinical Testing of a Food Additive; L.D. Stegink; July 1987
