Abstract
The effect of varying the concentration of wheat bran in the diet on the plasma and liver lipid levels, and bile acid metabolism of the rat was studied. Groups of male and female rats were maintained on a starch control, high bran, low bran, high fat and stock diet for periods of up to seventy-two weeks. The results of this study indicate that wheat bran supplementation had no overall effect on lipid or bile acid metabolism in these animals. Feeding a chemically standardised coarse wheat bran at a dose of 0.3 g/kg body weight per day over a period of six weeks to young healthy volunteers did not significantly alter plasma cholesterol and triglyceride concentrations in these subjects. However, plasma high-density lipoprotein cholesterol concentrations were significantly increased, while low-density lipoprotein cholesterol levels decreased during the six weeks of bran consumption. Plasma glucose concentrations were unaffected by the wheat bran supplementation, however, the concentration of glycosylated haemoglobin decreased in all subjects throughout the study; indicating that wheat bran might be effective in altering the rate of glucose absorption. Under in vitro conditions, wheat bran bound the carcinogens safrole and benzo(a)pyrene at the pH of the colon; indicating that bran may decrease the availability of these carcinogens for contact with the colon mucosa, and thus absorption at colonic pH. Binding occurred at acidic, neutral and basic pH values, although the percentage of carcinogen bound decreased as the pH became more basic. However, the in vivo studies are equivocal, and do not fully support the in vitro observations, and may be due to the metabolic alteration of the wheat bran by the intestinal microflora. Wheat bran supplementation had no effect on the plasma mineral concentration in the rat, although a complete mineral balance study was not performed. Both dephytinised and whole wheat bran bound inorganic iron in vitro, the amount bound depended on pH, the quantity of fibre, and the presence or absence of inhibitors of binding. Binding was minimal below pH 2 but rose rapidly above pH 3, to a maximum near pH 7.