FERMENTATION OF 13C-INULIN IS NOT AFFECTED BY A SINGLE ADMINISTRATION OF DIFFERENT WHEAT BRAN FRACTIONS IN HEALTHY SUBJECTS

Background and objectives: Wheat bran (WB) is a constituent of whole-grain products, which may be colonized by specific bacteria in the human colon and hereby stimulate cross feeding, leading to a more efficient carbohydrate fermentation and an increased butyrate production. We investigated to what extent WB fractions with different fermentation characteristics affect the fermentation of other carbohydrates (13C-inulin) in the colon. Methods: Ten healthy subjects performed four test days on which they consumed a standard breakfast, labelled with inulin- 14C-carboxylic acid, an oro-caecal transit time marker and supplemented with 10 g 13C-inulin and 20 g of a WB fraction (unmodified WB, WB with reduced particle size or destarched pericarp-enriched WB). On the control test day, no WB was consumed. Breath and blood samples were collected on regular time points for 14h to measure the start of fermentation and plasma 13C-labelled short chain fatty acid (SCFA; acetate, propionate, butyrate) concentrations, respectively. The relative proportions of acetate: propionate:butyrate were calculated to examine cross-feeding. Results: The amount of 13CO2 in the breath samples started to increase before the breakfast reached the colon (14CO2 increase in breath) (208.5 ± 29 min and 219 ± 24.2 min after the breakfast, respectively), indicating that the fermentation of 13C-inulin already started in the terminal ileum. In addition, fermentation of inulin resulted in higher plasma 13C-SCFA concentrations for approximately 8h, with maximal concentrations reached 6h after the breakfast, but compared to the control, SCFA levels were not further increased by WB (Wilcoxon signed ranks test; All p>0.1). Relative proportions of acetate:propionate:butyrate in plasma amounted 89:4:7, 89:4:7, 90:4:6 and 83:5:12 with unmodified WB, WB RPS, PE WB and the control, respectively, but were not changed by any WB fraction compared to the control, indicating that WB did not stimulate cross-feeding (Wilcoxon signed rank test; All p>0.1). Conclusions: Fermentation of 13C-inulin resulted in increased plasma SCFA for about 8h, suggesting that a sustained increase in plasma SCFA can be achieved by administering a moderate dose of carbohydrates three times per day. However, addition of a single dose of a WB fraction did not further increase the 13C-SCFA concentrations in plasma, nor stimulated cross-feeding between the gut bacteria.