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

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.