Repeated ingestion of aspartame-sweetened beverage: effect on plasma amino acid concentrations in individuals heterozygous for phenylketonuria.

It has been suggested that excessive use of aspartame (APM) (N-L-alpha-aspartyl-L-phenylalanine methyl ester) might grossly elevate plasma aspartate and phenylalanine concentrations in individuals heterozygous for phenylketonuria (PKUH). In study 1 six adult PKUH (three males; three females) ingested three successive 12-oz servings of beverage at 2-h intervals. The study was carried out in two parts in a randomized crossover design. In one arm the beverage was not sweetened. In the other the beverage provided 10 mg APM/kg body weight per serving. The addition of APM to the beverage did not significantly increase plasma aspartate concentration but did increase plasma phenylalanine levels 2.3 to 4.1 mumol/dL above baseline values 30 to 45 min after each dose. The high mean plasma phenylalanine level after repeated APM dosing (13.9 +/- 2.15 mumol/dL) was slightly, but not significantly, above the normal postprandial range for PKUH (12.6 +/- 2.11 mumol/dL). In study 2 six different adult PKUH ingested beverage providing 30 mg APM/kg body weight as a single bolus. The high mean plasma phenylalanine concentration and the phenylalanine to large neutral amino acid ratio were significantly higher when APM was ingested as a single bolus than when ingested as a divided dose.