Of 20 plasma amino acids measured, valine, leucine, isoleucine, tyrosine and phenylalanine were increased, and glycine decreased, in obese subjects compared with age- and sex-matched controls. The concentration of each of the amino acids elevated in obesity correlated directly with serum insulin. In addition, these were the amino acids most sensitive to the action of insulin in lowering plasma amino acid levels, as evidenced by a diminution in concentration after glucose infusion. Despite a significantly greater increment in serum insulin in the obese group, the magnitude of the decline in amino acids after glucose administration was identical in the two groups.

Hyperaminoacidemia appears to be a manifestation of the insulin ineffectiveness characteristic of obesity. Furthermore, hyperaminoacidemia may provide the feedback signal to the beta cell through which insulin resistance is accompanied by an appropriately augmented secretory rate of insulin.