Repeated ingestion of aspartame-sweetened beverages: further observations in individuals heterozygous for phenylketonuria.

Six adults heterozygous for phenylketonuria (PKU) ingested eight successive servings of unsweetened and aspartame (APM)-sweetened beverage at 1-hour intervals in a randomized, balanced, crossover design. In one part, the eight beverage servings were not sweetened. In the other, each of the eight beverage servings provided 600 mg of APM, a dose equivalent to the amount provided by 36 oz of an APM-sweetened diet beverage. Plasma aspartate concentration was not significantly increased after ingestion of unsweetened or APM-sweetened beverage. Similarly, ingestion of the unsweetened beverage had no significant effect on plasma phenylalanine concentration. However, ingestion of APM-sweetened beverage significantly increased plasma phenylalanine concentrations 2.35 to 4.03 mumol/dL above baseline 30 minutes after ingestion. Plasma phenylalanine values reached a steady-state after administration of five servings of APM-sweetened beverage and were slightly, but significantly higher than usual postprandial values for adults heterozygous for PKU. Similarly, the ratio of the plasma phenylalanine concentration to the sum of the concentration of the large neutral amino acids was significantly higher than usual postprandial values. Blood methanol and formate concentrations remained within normal limits. These data indicate that a fasting adult heterozygous for PKU could consume the equivalent of 24 12-oz servings of APM-sweetened beverage over an 8-hour period and only increase plasma phenylalanine concentration to a modest degree.