Effects on metabolic and hormonal parameters of monosodium glutamate (umami taste) ingestion in the rat.

Abstract Umami taste appears to signal, at the gustatory level, the intake of proteins, therefore the working hypothesis was: does umami taste of a monosodium glutamate (MSG) solution elicit changes in both glucagon and insulin release, similar to those elicited by aminoacids, and consequently, changes in plasma glucose and in overall cellular metabolism? In a first experiment, rats were equipped with indwelling jugular and oral catheter and serial samplings were made in the free moving, undisturbed rat before and after an oral or IV infusion of MSG (0.05M). None of the plasma parameters showed any significant response. In a second experiment, energy expenditure was monitored by means of an original computer-based calorimeter capable of calculating, besides the classical parameters, resting metabolism in a moving animal (designated by background metabolism). The addition of MSG to a low calorie, low-protein meal did not modify background metabolism or respiratory quotient. Therefore MSG ingestion does not by itself affect plasma levels of hormones of glucose and protein metabolism, total metabolism rate, or nutrient utilization. However, examination of individual data and those from a pilot experiment for future work suggests that MSG becomes an efficient metabolic effector if added to a caloric diet, and so enhances proper thermogenesis of macronutrients.