What Is Fiber?

Fiber, or "bulk" or "roughage," is a substance found in plants. Dietary fiber -- the kind you eat -- is found in fruits, vegetables, and grains. It is an important part of a healthy diet. Dietary fiber adds bulk to your diet. Because it makes you feel full faster, it can be helpful in controlling weight. Additionally, fiber aids digestion, helps prevent constipation, and is sometimes used for the  treatment of diverticulosis, diabetes, and heart disease.

There are 2 forms of fiber: soluble and insoluble.

Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. Soluble fiber has been scientifically proven to lower cholesterol, which can help prevent heart disease.

Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It appears to speed the passage of foods through the stomach and intestines and adds bulk to the stool.

(Information on this page was adapted from the MedlinePlus Medical Encyclopedia, a service of the U.S. National Library of Medicine and the National Institutes of Health.)