Role of Dietary Free Glutamate in Gastrointestinal Function

Glutamate is a non-essential amino acid that confers umami taste. Recently, several taste receptors for umami taste have been identified in the oral cavity as well as in the gastrointestinal tract. Gustatory stimulation of the tongue by glutamate activates vagal gastric, pancreatic, and hepatic efferent nerves. In the gastrointestinal tract, glutamate excites afferent fibers of the abdominal vagus nerve. Recent data suggest the possibility that a chemosensory system similar to that found in the mouth is also present in the stomach and small intestine and that this system aids in regulating gastrointestinal functions. In this review, we have summarized the known effects of dietary free glutamate on gastrointestinal functions such as gastric secretion and gastrointestinal motility, and we explore the possibility of application of glutamate as a medical food supplement. Fortification of protein or amino acid rich diets with free glutamate enhances gastric secretion and promotes gastric emptying. Current results indicate that free glutamate modulates gastrointestinal functions, especially gastric digestion, via cephalic or gastrointestinal phase responses. Dietary supplementation of enteral nutrition with free glutamate could help to prevent complications of these diets, especially diarrhea.