Postprandial Plasma Free Methionine as an Indicator of Dietary Methionine Adequacy in the Human Infant

Abstract

Fasting plasma free methionine (Met) levels were not different in infants consuming Met-deficient and Met-adequate diets. We have now measured plasma free amino acids (AA) just before and 1, 2, 3 and 4 hours after consumption of a single meal which was either limiting in Met, limiting in another AA (lysine or threonine), or probably not limiting in any AA. In the first group postprandial plasma Met was almost invariably below fasting, particularly at 3 and 4 hours. In the second group postprandial Met was almost invariably above fasting, while in the third group (balanced diets) it was generally close to the fasting level, but with wider variation. When plasma Met is expressed as its molar fraction of total essential and semiessential AA, it discriminates more sharply between the different diets, notably at 4 hours.