Also many will tell you that the bran scours the intestinal system of flora and tho it will assit elimination it actually causes dependence because its not fiber that we need for healthy elimination its intestinal flora.
Oat bran is considered a "soft" fiber, not a hard fiber like wheat bran. So it is not hard on the intestines. And the cellulose of the oat bran provides a food sources to feed the flora. The flora ferment the fibers to break down the cellulose, a long chain sugar molecule, in to simpler sugars they can feed on. So we need fibers to keep the flora healthy, and so the flora can generate their beneficial acids. They do not cause a dependence though like anthraquinone stimulant laxatives (senna, cascara sagrada, rhubarb root, cape aloe).