Fiber used in dietary nutrition is from plants. The part of plants that can not be digested and thus pushes food through the digestive system. Fiber plays a big role in how the digestive tract absorbs nutrients. Dietary fiber can be water-soluble and fat-soluble. The water-soluble fiber can not be digested but ferments due to bacteria. Water-soluble fiber also absorbs water to become thicker as it passes through the body. Fat-soluble fiber doesn't ferment like water-soluble fiber and is thicker. Both types of fiber can be found in all plant foods, although one type of fiber is usually more abundant than the other. Dietary fiber promotes health of the digestive tract by increasing bulk, softening stool, and shortening time in the intestinal tract.