Fiber is the material that gives plants texture and support. Dietary fiber is found in many plant foods, including fruits, vegetables, beans, nuts, and whole grains. Although fiber is primarily made up of carbohydrates, it does not have a lot of calories and usually is not broken down by the body for energy. Fiber is sometimes called roughage.
There are two types of fiber: soluble and insoluble. Insoluble fiber, as the name implies, does not dissolve in water because it contains high amounts of cellulose. Insoluble fiber is found in grain brans, fruit pulp, and vegetable peels or skins. Soluble fiber is the type of fiber that dissolves in water. It can be found in a variety of such fruits, grains, and vegetables as apples, oatmeal and oat bran, rye flour and dried beans.
Although the two types of fiber share some common characteristics such as being partially digested in the stomach and intestines and being low in calories, each type has its own specific health benefits. Insoluble fiber speeds up the movement of foods through the digestive system and adds bulk to the stools; it helps to treat constipation or diarrhea and prevents colon cancer. On the other hand, only soluble fiber can lower blood cholesterol levels. This type of fiber works by attaching itself to the cholesterol so that it can be eliminated from the body. This process prevents cholesterol from recirculating and being reabsorbed into the bloodstream.
Mai Tran, Teresa G. Odle, The Gale Group Inc., Gale, Detroit,