Postprandial changes in small bowel water content in healthy subjects and patients with irritable bowel syndrome

Postprandial symptoms are common in patients with irritable bowel syndrome with diarrhea (IBS-D) and could be diet related. We studied postprandial changes in distribution of water in the upper gastrointestinal tract of healthy volunteers (HVs) and patients with IBS-D after contrasting meals.

In study 1, 11 HVs consumed 350-mL test meals with 5% mannitol (unabsorbable) or 5% glucose (readily absorbed). In study 2, 17 HVs consumed a 331-kcal meal, with or without 15 g bran. In study 3, 26 patients with IBS-D consumed the study 2 diet with bran meal. All subjects underwent serial magnetic resonance imaging analysis.

In study 1, subjects' small bowel water content (SBWC) increased after the mannitol but not glucose meals, reaching 381 mL (interquartile range, 343-491 mL) and 47 mL (18-78 mL), respectively, 40 minutes after eating (P < .001). In study 2, SBWC initially decreased after both meal types and then increased, plateauing at 180-405 minutes and was greater after the bran meal (P = .02). In study 3, fasting and postprandial SBWC was lower in IBS-D than in HVs (P < .05 and P < .0001, respectively). Patients with IBS-D had faster orocecal transit times (135 minutes; 90-180 minutes) compared with HVs (225 minutes; 203-293 minutes; P < .0001) and reduced terminal ileum diameter (P < .003).

Postprandial SBWC initially decreases, because of rapid, nutrient-driven fluid absorption, and then increases after a mixed liquid/solid meal. Patients with IBS-D have reduced fasting and postprandial SBWC with faster transit, possibly indicating increased small intestinal tone.