Fiber-supplemented enteral formula slows intestinal transit by intensifying inhibitory feedback from the distal gut

Because an increase in flow rate accelerates intestinal transit, a reduction in the flow rate of formula delivery is recommended frequently for treatment of diarrhea that develops during enteral feeding. Because intestinal transit is slowed by nutrient-triggered inhibitory feedback, the rate of intestinal transit during enteral feeding may depend on a balance between the accelerating effect of flow and the inhibiting effect of the nutrient load. The addition of fiber to a formula may alter this balance. By delaying absorption of nutrients, fiber may extend the length of small intestine exposed to nutrients and thereby trigger more intense inhibitory feedback. To determine whether the addition of fiber favors nutrient-triggered inhibition over flow-driven acceleration, we studied intestinal transit after perfusion of a low-residue enteral formula compared with a fiber-supplemented formula at two perfusion rates (50 or 100 mL/h for 2 h) into the duodenum of dogs each with both a duodenal and midgut fistula. With the low-residue formula, intestinal transit accelerated when the flow rate increased from 50 to 100 mL/h (P < 0.05). With the fiber-supplemented formula, however, intestinal transit was inhibited regardless of the flow rate. To determine whether the fiber-supplemented formula inhibited intestinal transit by displacing nutrients distally, we compared intestinal transit when the two formulas, delivered at 100 mL/h, were diverted completely at the midgut fistula. Intestinal transit of the fiber-supplemented formula increased by 400%, eliminating the difference in intestinal transit speed between the two formulas. We concluded that the fiber-supplemented formula slowed intestinal transit by intensifying inhibitory feedback from the distal gut.