An oral amino acid loading test before and after intestinal bypass operation for morbid obesity

Blood samples were taken from six overweight women after an overnight fast on three different occasions, before an jejunoileal bypass operation and 1 and 6 months after the operation. The preoperative levels of several plasma free amino acids were significantly elevated, e.g. leucine, isoleucine, valine, lysine, phenylalanine, tyrosine, proline and glutamic acid. One month after the operation all indispensable plasma amino acid concentrations had fallen, in particular the levels of the branched-chain amino acids (BCAA), lysine and tryptophan. Among the dispensable amino acids, plasma tyrosine, arginine and ornithine concentrations were significantly reduced. No further changes of significance were observed in samples taken 5 months later. A close correlation was observed between the plasma levels of retinol-binding protein (RBP) and thyroxine-binding prealbumin (TBPA). One month after the operation the levels of RBP and TBPA had fallen slightly in two subjects and substantially in one subject. A test diet, containing crystalline amino acids, glucose and fat emulsion was given before operation and twice after the operation. Plasma amino acid changes were studied for a period of 2 hours after the meal. The increases in plasma levels following the test meal were lower for many amino acids after the operation. A linear correlation was found between the postprandial increases in BCAA concentrations and the levels of RBP and TBPA. By using complete, carefully defined diets in loading tests, it should be possible to screen for glucose tolerance and amino acid and lipid malabsorption.