BLOOD AMINO ACID STUDIES: IV. SOME FACTORS AFFECTING PLASMA AMINO ACID LEVELS IN HUMAN SUBJECTS

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Abstract
Free lysine, methionine, threonine, and tryptophan were determined in small samples of blood obtained by finger punch from human subjects. The levels of the four amino acids rose rapidly after the subjects consumed protein as baked halibut; the extent and duration of the increases were roughly proportional to the amount of protein eaten and to the amino acid composition of the protein. The increases of free methionine and threonine in plasma were somewhat less when butter was taken with fish but starch (as potato) or sucrose did not affect the values. Other foods tested at the 19.0-g level of protein included egg, a commercial breakfast cereal, and the same cereal plus milk. In general the increase or decrease of each amino acid tested was related to the amount of that amino acid in the test food. The plasma amino acid (PAA) ratio of Longenecker and Hause was calculated for each food and was useful in evaluating the increase or decrease of each specific amino acid. The present work appears to offer a practical procedure for studying the plasma amino acid response of groups of human subjects to variations in dietary protein.