Aspartame-Sweetened Beverage: Effect on Plasma Amino Acid Concentrations in Normal Adults and Adults Heterozygous for Phenylketonuria

Twelve normal subjects ingested either unsweetened beverage (n = 6) or beverage providing 4 mg/kg body weight as aspartame (APM) (n = 6). Neither beverage had any significant effect on plasma aspartate or phenylalanine concentrations. After this study, eight normal and six obligate phenylketonuric (PKU) heterozygous adults each ingested a 354-mL (12-oz) beverage serving on two occasions in a randomized cross-over design. On one occasion the beverage was not sweetened; on the other occasion, the beverage provided 10 mg APM/kg body weight. Plasma amino acid concentrations were measured throughout the 2-h study period. The addition of 10 mg APM/kg body weight to the beverage had no significant effect on plasma aspartate concentration. APM ingestion increased plasma phenylalanine levels of normal subjects from a mean ± SD baseline value of 5.09 ± 0.82 µmol/dL to a high mean value of 6.73 ± 0.75 µmol/dL. In PKU heterozygous subjects the plasma phenylalanine level increased from a mean ± SD of 9.04 ± 1.71 to a high mean value of 12.1 ± 2.08 µmol/dL. The data indicate ready metabolism of the aspartate and phenylalanine portion of APM when administered at levels likely to be ingested by individuals who drink diet beverages.