Postingestional effects of a high-protein diet on the regulation of food intake in monkeys.

Using a system in which the composition of an intragastric diet could be manipulated while oral factors were kept constant, we studied the effect of a high-protein diet on food intake. Four adult rhesus monkeys with chronically implanted intragastric cannulas were trained to use suction-activated food pumps that were monitored by computer so feeding pattern could be assessed over periods averaging 4 wk each. Each suck delivered the oral control diet while simultaneously activating a second pump, which delivered a second diet directly into the stomach, resulting in net diet compositions of either 14% or 50% protein. The calorie intake was consistently reduced by 24.7 +/- 1.6% when the high-protein diet was fed. The effect on intake was not due to increased diet osmolality. A doubling in plasma branched-chain amino acid concentration occurred when the high-protein diet was fed. These data indicate that feeding a high-protein diet results in a physiological appetite suppression, possibly mediated through branched-chain amino acids.