INTERACTIVE EFFECTS OF OAT BRAN AND WHEAT BRAN ON SERUM AND LIVER LIPIDS AND COLONIC PHYSIOLOGY

Studies in humans and rats show that oat bran lowers serum cholesterol whereas wheat bran does not. In contrast, wheat bran is more protective against experimentally induced colon cancer than is oat bran. The purpose of the present study was to determine whether a combination of oat bran and wheat bran could both lower serum cholesterol and positively affect colon physiology. Sixty male Sprague-Dawley rats (12 per group) were fed sufficient fiber from oat bran and wheat bran to result in the following amounts and combinations of dietary fiber in their diets: 1) 4% from oat bran + 4% from wheat bran (4 + 4); 2) 6% from oat bran + 2% from wheat bran (6 + 2); 3) 4% from oat bran only (4 OB); 4) 4% from wheat bran only (4 WB). Results were compared to a control supplemented with 8% cellulose. The diet with the highest amount of oat bran (6 + 2) resulted in the lowest serum cholesterol value (143 +/- 5 mg/100 ml), which was significantly lower than the control (180 +/- 17) and 4% from wheat bran only (4 WB) (230 +/- 10, [P < 0.01]). Similar amounts of oat bran resulted in similar cholesterol values despite the presence of wheat bran: 157 +/- 5 (4 + 4) compared to 161 +/- 5 (4 OB). In the colon, the addition of wheat bran to the oat bran diet did not mitigate the fermentative effects of oat bran, even though wheat bran was a better bulking agent, assessed by a greater fecal dry weight (4.29 +/- 0.21 g for 72 hr compared to 3.63 +/- 0.21 g, [P < 0.01]), probably due to a higher proportion of insoluble fiber. This study shows that adding wheat bran to oat bran does not negate the positive effects of the latter on serum lipids. However, neither does it overcome the negative effects of oat bran on colon physiology.