The effect of wheat bran particle size on laxation and colonic fermentation

Objective: Due to perceived inferior fecal bulking ability, finely ground w heat bran is not recommended for treatment of colonic disorders, despite po ssible short chain fatty acid generation with potential benefits for coloni c mucosal health. We therefore tested the effects of very fine particle siz e wheat bran on colonic function. Methods: Two studies, each with three phases, were undertaken in healthy su bjects in a randomized crossover design. In one study (metabolic, n=23) sub jects took three diets containing either an additional 19 g/d dietary fiber with mean particle size (MPS) 50 mu m or 758 mu m in bread or a control lo w fiber bread. In the other study where the supplement was provided as a br eakfast cereal (ad libitum, n=24) the respective wheat bran MPS were 692 mu m and 1158 mu m and the control was low fiber. Fecal collections were obta ined during the last week of each diet. In the metabolic study, fecal shea chain fatty acids were measured and 12-hour breath gas collections obtained . Results: In both studies, wheat bran supplements significantly increased fe cal bulk compared to the control (p<0.004), with no significant differences between brans of different particle size and no differences in fecal water content. However, higher fecal butyrate concentrations (p<0.007), butyrate output and breath CH, levels (p=0.025) were seen on the low MPS wheat bran compared to the other two treatments, suggesting increased bacterial ferme ntation. Conclusions: Fine MPS wheat bran is an effective fecal bulking agent and ma y have added advantages if increased butyrate concentrations promote coloni c mucosal integrity.