Repeated ingestion of aspartame-sweetened beverage: effect on plasma amino acid concentrations in normal adults.

Aspartame (APM) is a dipeptide sweetener (L-aspartyl-L-phenylalanine methyl ester). It has been suggested that excessive use of the product might elevate plasma aspartate and phenylalanine concentrations. Eight normal adults (four male, four female) ingested three successive 12-oz servings of APM-sweetened beverage at two-hour intervals. The study was carried out in two parts in a randomized cross-over design. In one study the beverage was not sweetened. In the other, the beverage provided 10 mg APM/kg body weight per serving. Plasma amino acid concentrations were measured throughout the six-hour study period. The addition of APM to the beverage had no significant effect on plasma aspartate concentration. APM addition did increase plasma phenylalanine levels 1.64 to 2.05 mumol/dL above baseline values (5.09 +/- 0.82 mumol/dL) 30 to 45 minutes after each dose. However, plasma phenylalanine levels did not exceed normal postprandial values at any time. The data indicate ready metabolism of APM's amino acid content when administered at levels likely to be ingested by individuals who are heavy users of such beverages.