Dietary Glutamic Acid Increased Postprandial Leucine Availability in Protein Malnourished Rats

Abstract

Glutamic acid (Glu), the most abundant amino acid in food proteins, is major intestinal energy source. Recently we have found that Glu removal from foods reduced dietary leucine (Leu) availability by reducing its oxidation. The present study investigated roles of dietary Glu on Leu metabolism in details using protein malnourished rats.Fischer strain male rats were fed normal amino acid (AA) defined diet containing 4% Glu or low AA diet (50% reduction) for 1 week. Then, the rats in each dietary group were divided into two groups and given daily amount of experimental diets with or without Glu in which all the Leu was replaced with [1‐13C]Leu. After 24h collection of expired air samples, blood and tissue samples were harvested. Breath 13CO2 and [1‐13C]Leu incorporation in tissue proteins were analyzed by IRMS and GCMS, respectively.Feeding of low AA diet reduced dietary Leu oxidation markedly. Glu removal from low AA diet significantly enhanced dietary Leu oxidation and reduced its incorporation in liver protein and plasma albumin but not kidney or muscle proteins, indicating decrease in dietary Leu availability for hepatic protein synthesis in these animals presumably due to increase in its intestinal oxidation. Besides, the effects of Glu removal from normal AA diet were not apparent. These results suggest Leu‐sparing effects of dietary Glu by reducing postprandial Leu oxidation especially in protein malnutrition.