To determine whether the addition of an inulin and oligofructose mixture (FOS) to a diet containing oat bran lowered serum cholesterol more than oat bran or FOS alone, we conducted a randomized controlled crossover trial at a teaching hospital clinic. Twenty-six hypercholesterolemic adults each took three 4-week treatments: oat bran bread plus 10 grams FOS, oat bran bread plus 10 g maltodextrin, and 10 grams FOS plus wheat bran bread, with 1-week minimum washout between phases. Subjects followed an Adult Treatment Panel III step 2 diet. Serum lipids, colonic microflora, breath gases, and fecal short-chain fatty acids were measured. No treatment reduced serum lipids and no differences between treatments were seen. Changes from time zero in bifidobacteria did not relate to changes in LDL-Cholesterol (P≥0.408). In conclusion, we found no effects of FOS or oat bran on serum lipids. This may relate to beta-glucan hydrolysis by gluten added to the bread.