Wheat bran differs greatly from oat bran and the difference lies in the composition of its fibers. Unlike the highly soluble ones of oat bran, wheat bran fibers are insoluble. Thus, while oat bran fibers absorb water to the point of becoming a sponge-like substance soft to the touch and pliable throughout the digestive tract, wheat bran fibers remain hard and dry. In this way, wheat bran is more irritating to the lining of the colon, which allows it to speed up bowel function and fight constipation. But this benefit could backfire and cause damage to sensitive bowels or worse, irritable bowels. It's the high solubility of the fibers in oat bran, which are accountable for its absorption capacity and viscosity, that allow it to yield a rapid satiation, a long-lasting feeling of fullness and a loss of calories into the stools. This explains its valuable role in fighting excess weight, obesity and diabetes.