Fiber refers to that portion of a plant that cannot be broken down by the human digestive tract. There are two methods used to measure fiber. One gives crude fiber and the other gives dietary fiber. Dietary fiber is a more accurate measure of the amount of undigestible fiber in foods. While crude fiber may be reported on some food labels, it will be less than the amount of dietary fiber available.
Foods vary in the type and components of fiber that they contain.
The components and their effects are described in the table. They appear to act in different ways in the body. For example, soluble fibers like pectins and guar gum can help lower serum cholesterol while insoluble fibers like cellulose may help prevent colon cancer. Both types absorb water and can combat constipation by softening the stool. The primary effects of fiber that occur in the gastrointestinal tract begin with the mouth, and progress through the stomach and intestines.