Dietary poorly absorbed, short-chain carbohydrates increase delivery of water and fermentable substrates to the proximal colon

P>Background Functional gut symptoms are induced by inclusion and reduced by dietary restriction of poorly absorbed short-chain carbohydrates (FODMAPs), but the mechanisms of action remain untested. Aims To determine the effect of dietary FODMAPs on the content of water and fermentable substrates of ileal effluent. Methods Twelve ileostomates without evidence of small intestinal disease undertook two 4-day dietary periods, comprising diets differing only in FODMAP content in a randomized, cross-over, single-blinded intervention study. Daytime (14 h) ileal effluent was collected on day four of each diet. Patients rated effluent volume and consistency on a 10-cm visual analogue scale. The FODMAP content of the diet and effluent was measured. Results Ingested FODMAPs of 32% (range 6-73%) was recovered in the high FODMAP diet effluent. Effluent collection weight increased by a mean of 22% (95% CI, 5-39), water content by 20% (2-38%) and dry weight by 24% (4-43%) with the high compared to low FODMAP diet arm. Output increased by 95 (28-161) mL. Volunteers perceived effluent consistency was thicker (95% CI, 0.6-1.9) with the low FODMAP diet than with the high FODMAP diet (3.5-6.1; P = 0.006). Conclusions These data support the hypothetical mechanism; FODMAPs increase delivery of water and fermentable substrates to the proximal colon.