Modulating effect of Sustagen on plasma glutamate concentration in humans ingesting monosodium L-glutamate

It has been suggested that monosodium L-glutamate (MSG) addition to meals would significantly increase plasma glutamate concentrations compared to values noted after ingestion of protein-bound glutamate. To test this hypothesis, plasma amino acid concentrations were measured in six normal adults ingesting a ready-to-feed liquid meal (Sustagen) containing added MSG at 0, 100, and 150 mg/kg body weight (Latin square design), and compared to plasma values noted after ingestion of 150 mg/kg body weight MSG in water. The mean (+/- SD) peak plasma glutamate concentrations after ingestion of meals providing 0, 100, and 150 mg/kg body weight MSG were 6.64 +/- 1.99, 11.2 +/- 4.89 and 10.8 +/- 3.10 mumol/dl, respectively. Erythrocyte glutamate concentrations were unchanged after each meal. Peak plasma glutamate concentrations after ingestion of meals with added MSG were similar to those noted in normal adults ingesting a similar quantity of protein-bound glutamate. In contrast, ingestion of MSG in water (150 mg/kg body weight) markedly increased the mean (+/- SD) peak plasma glutamate concentration to 71.8 +/- 35.7 mumol/dl. Similarly, the area under the plasma glutamate concentration-time-curve was significantly higher. MSG ingestion with meals results in lower plasma glutamate concentrations than ingestion of equivalent doses in water.