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Fiber is a type of carbohydrate present in all foods derived from plants, including whole grains, fruits, vegetables, beans, nuts and seeds. It is not digested or absorbed into the bloodstream and does not add calories to a person’s diet or provide energy for the body. However, fiber provides numerous health benefits to the body.

Fiber is a key component of a healthy diet and contributes to digestive health and appetite control. It also helps reduce blood cholesterol and blood sugar levels in the body and has been linked to preventing or controlling chronic diseases such as heart disease, diabetes, obesity and possibly some forms of cancer.

Fiber is divided into two types, based on its solubility, or ability to dissolve in water:

• Soluble fiber. Forms a gel when mixed in a liquid. Soluble fiber slows digestion and helps the body absorb various nutrients.
  
  
• Insoluble fiber. Provides structure to plant cell walls and does not dissolve in liquids. Insoluble fiber adds bulk to stool, preventing constipation and allowing stool to pass more quickly.

Fiber also can be classified according to its chemical structure. Examples of fiber categorized in this way include cellulose, hemicelluloses, gums and mucilages, lignan, pectin, and restricted starches.

High-fiber foods are a rich source of vitamins and minerals, and are generally low in total fat, saturated fat, cholesterol and salt. Foods high in fiber are known to help promote regular bowel movements and generally have few calories. They also contribute to a feeling of fullness.

Fiber can be found in all plant foods. However, it is not found in any foods that come from animals, including meat, fish, poultry, milk, milk products and eggs. Most foods that contain fiber contain both soluble and insoluble fiber, although the balance leans toward one type or the other. Fiber also is available in supplement form. However, experts generally advise most people to use dietary sources of fiber rather then supplements.

To get adequate amounts of fiber, the U.S. Dietary Guidelines and the Dietary Reference Intakes (DRIs) indicate that people should eat a variety of fruits, vegetables and whole-grain products daily. Helpful tools to increase intake of dietary fiber can be found on food labels.