Protein absorption depends on load-dependent inhibition of intestinal transit in dogs.

Ileal perfusion of protein slows intestinal transit. Because optimal absorption of nutrients requires adequate time in contact with the mucosa, slowed intestinal transit may increase protein absorption by increasing the residence time of nutrients in the small intestine. Although protein supplements are routinely added to enteral feeding to correct protein malnutrition, little information is available on the effect of increasing the load of protein on intestinal transit and the efficiency of protein absorption. In six dogs equipped with duodenal and midintestinal fistulas, intestinal transit and the efficiency of protein absorption (percentage protein absorbed as estimated from the output of midintestinal fistula) were compared during intestinal perfusion with 0-, 50-, 100-, and 200-g/L solutions of a whey-based protein supplement. We found that intestinal transit slowed in a load-dependent fashion (P < 0.05); the amount of protein absorbed within the proximal one-half of the small intestine increased in a load-dependent fashion (P < 0.05) as intestinal transit slowed, and the percentage protein absorbed (reflecting the efficiency of protein absorption) was maintained at a high and nearly constant value of 66.5-72.5% across protein loads of 9-36 g. We conclude that enhanced protein absorption is associated with a load-dependent inhibition of intestinal transit.