Plasma Amino Acid Concentrations in Normal Adults Fed Meals with Added Monosodium L-Glutamate and Aspartame

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Abstract
Aspartame is a dipeptide sweetener containing aspartate. It has been suggested that aspartame addition to meals containing large amounts of monosodium L-glutamate (MSG) would result in a rapid rise in plasma glutamate and/or aspartate concentrations and increase the potential for dicarboxylic amino acid-induced toxicity. Six normal adult subjects were fed three hamburger and milk shake meals providing protein at 1 g/kg body weight in a Latin square design. One meal had no additions, the second provided MSG at 150 mg/kg body weight, and the third provided MSG at 150 mg/kg body weight and aspartame at 23 mg/kg body weight. The addition of MSG alone significantly increased plasma glutamate + aspartate concentration above values noted after ingestion of the meal alone. Aspartame addition to meals already containing MSG did not further significantly increase plasma glutamate + aspartate concentration above values noted when only MSG was added. However, aspartate addition did significantly increase the mean plasma phenylalanine concentration above values noted after ingestion of the meal alone or the meal with added MSG, reflecting aspartame's phenylalanine content. The data do not support the suggestion that aspartame addition to high protein meals already containing large amounts of MSG, will promote a rapid and dangerous rise in plasma glutamate and aspartate concentrations.