Fiber is a dietary material containing substances that are resistant to the action of digestive enzymes. Fiber adds bulk and texture to foods. As it passes through the body, fiber helps your system stay regular, and that’s why many doctors recommend fiber to help manage constipation. All fiber is not the same, and it doesn’t work in your system the same way, either. Fiber can be categorized by two distinct characteristics: Insoluble or soluble Insoluble fiber doesn’t absorb water; soluble fiber does. Both help material move through your digestive tract, but soluble fiber, like Citrucel, can help give stool a softer, bulkier consistency that’s easier to pass.