Insoluble fiber adds bulk to your stool, helping the stool pass more quickly through the intestines. Most plant foods contain some of each kind of fiber. Foods containing high levels of soluble fiber include dried beans, oats, oat bran, rice bran, barley, citrus fruits, apples, strawberries, peas, and potatoes. Foods high in insoluble fiber include wheat bran, whole grains, cereals, seeds, and the skins of many fruits and vegetables.