Emerging aspects of dietary glutamate metabolism in the developing gut.

Glutamate is a major constituent of dietary protein and is also consumed in many prepared foods as a flavour additive in the form of monosodium glutamate (MSG). Evidence from human and animal studies indicates that glutamate is the major oxidative fuel for the gut and that dietary glutamate is extensively metabolized in first-pass by the intestinal enterocytes. Glutamate also is an important precursor for bioactive molecules, including glutathione, and functions as a key neurotransmitter. The central importance of glutamate as an oxidative fuel may have therapeutic potential for improving function of the infant gut, which exhibits a high rate of epithelial cell turnover. Our recent studies in infant pigs show that when MSG is fed at higher (4-fold) than normal dietary quantities, the majority (approximately 70%) of glutamate molecule is either oxidized as energy or metabolized by the mucosa into other nonessential amino acids. Our results also showed that at high dietary intakes the rate of MSG absorption is higher when given via the intragastric compared to intraduodenal route. This intriguing finding implies that gastric glutamate transport may be physiologically significant and warrants further research into the role of MSG in gastric development and function during infancy.