Circadian variations in plasma and erythrocytes glutamate concentrations in male adults on a diet with and without added monosodium glutamate.
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Date
2000-04-01
Authors
Po-Jung Tsai and Po-Chao Huang,
Journal Title
Journal ISSN
Volume Title
Publisher
American Society for Nutrition
Abstract
This study evaluated the effect of monosodium glutamate (MSG) ingestion as a component of the
diet on the 24-h variations in plasma and whole-blood glutamate (GLU) concentrations in healthy adult men. In the
first arm of the study, subjects were given test meals without added MSG for 3 d. Protein and energy intakes of
the subjects were 1.5 g and 40 kcal/(kg body weightzd), respectively. On d 3, blood samples were collected over
the 24-h period. One week later, the same protocol was repeated, except that 100 mg/(kg body weightzd) MSG was
added to the meals (15, 40 and 45 mg/kg body weight to breakfast, lunch and dinner, respectively). Both plasma
and whole-blood samples were analyzed for free amino acids. Unlike large neutral amino acids, which experienced
high peak plasma concentrations at 2100–2300 h, the circadian variations in plasma GLU concentrations were
small, varying between 33 and 48 mmol/L on days in which no MSG was fed, and between 32 and 53 mmol/L on
days in which MSG was added to the meals. In both trials, plasma GLU concentration increased (P , 0.01) after
lunch and dinner, and decreased early in the morning (P , 0.05). Calculated erythrocyte GLU concentrations varied
between 500 and 640 mmol/L, with or without MSG addition to the meals. The rather low plasma GLU concentrations over the 24-h period, despite high dietary intake of MSG, indicate that dietary MSG is metabolized very
rapidly.