Monosodium L-glutamate added to a high-energy, high-protein liquid diet promotes gastric emptying

Background: Free glutamate activates taste receptors on nerves in the oral cavity to elicit a unique taste known as umami. Recently, umami taste receptors were also found in the gastric mucosa. Although reports suggest that mucosal receptors may respond to free glutamate to modulate gastric function, no evidence of any effect on gastric emptying has been documented. Objective: We hypothesized that glutamate may act as a modulator of gastric function. We studied the effects of L-glutamate enrichment of a protein-rich liquid meal, and similar enrichment of an equicaloric carbohydrate meal or noncaloric water, on gastric emptying. Design: Ten healthy men were enrolled. Nine of the 10 subjects included in the study ingested all test meals with and without monosodium L-glutamate ( MSG), and the remaining subject ingested only the protein-rich meals with and without MSG. All experimental and control liquid meals included [1-C-13] sodium acetate as a tracer. After a test meal or water was ingested, C-13 breath tests were performed to estimate gastric emptying. Results: MSG enrichment not only resulted in a significant decrease in the mathematically simulated half-excretion ( emptying) time of a protein-rich meal, but also increased the area under the curve (%dose/h) significantly. In contrast, MSG had no significant effect on the gastric emptying of a carbohydrate meal or a noncaloric water meal. Conclusions: Enrichment with MSG facilitated gastric emptying of a protein-rich meal exclusively, which suggests that free glutamate is important for protein digestion and may be helpful in the management of delayed gastric emptying. Am J Clin Nutr 2009; 89: 431-5.