Wheat bran consists of the outer coats of the wheat grain, which can be separated from the germ and various grades of flour during the milling process. The National Research Council’s 1989 volume on diet and health also discusses wheat bran consumption and cancer risk. The animal studies overwhelmingly support the proposition that wheat bran has a protective effect against colorectal carcinogenesis. A number of studies have sought to quantify and measure changes in bile acid concentrations brought about by wheat bran intake. The increase in fecal bile acid excretion accompanying a significant decrease in fecal bile acid concentrations has been explained as due to increased stool bulk from wheat bran fiber. Wheat bran is able to increase fecal bulk because it traps water, increases the amount of undigested material, and increases the bacterial cell mass in the stool.