Comparison of ileal effluents, dietary fibers, and whole foods in predicting the physiological importance of colonic fermentation.

An in vitro fermentation system that simulates the human colon was used in conjunction with the human ileostomy model to determine whether whole foods or dietary fiber isolates from the same foods could be used in lieu of ileal effluent to estimate the daily colonic production of short chain fatty acids (SCFA). A basal diet and a test food were fed for 3 days to a healthy ileostomate, and the ileal effluent was collected. Dietary fiber intake significantly increased ileal dry matter, ash, protein, and available carbohydrate (total carbohydrate minus dietary fiber) (p less than 0.05). Basal diet, test foods, ileal effluents, and dietary fiber isolates then were fermented in vitro with mixed human fecal microflora for 24 h, and SCFA production (mmol SCFA/g organic matter) was measured. SCFA production from ileal effluent significantly correlated with that from dietary fiber isolates (r = 0.86, p less than 0.05), but not with that from whole foods. Therefore, dietary fiber isolates, rather than whole foods, can provide the closest estimates of colonic SCFA production when ileostomates are not available. Test foods significantly changed molar ratios of individual SCFA within the ileal effluent and dietary fiber isolate groupings (p less than 0.05). In view of the different ileal loads arriving in the colon, we conclude that large differences in SCFA production probably depend on the food consumed.