Abstract
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.
Highlights
Glutamate is the most abundant amino acid and is widely distributed in vegetables, meats, and fish
We examine the evidence for effects of dietary free glutamate on gastrointestinal functions such as gastric secretion and gastrointestinal motility, and the possibility of application of free glutamate to promote digestion of medical diets
We reported that when free glutamate is co-applied with a liquid diet, its effect on gastric emptying does not support its activity as a prokinetic agent and glutamate addition does not cause a discomfort sensation due to enhanced gastric emptying
Summary
Hiroaki Zai1, Shinji Somekawa2, Hisayuki Uneyama2 and Motoyasu Kusano3* 1Department of Gastroenterology, Hotaka Hospital, 378-0133 Gunma, Japan 2Institute for Innovation, Ajinomoto Company, Inc., 210-8681 Kanagawa, Japan 3Department of Endoscopy and Endoscopic Surgery, Gunma University Hospital, 371-0044, Gunma, Japan
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