Fiber, a form of carbohydrate that is not digestible, is a non-nutritive but essential component of a healthy diet. Fiber is not a single compound, but a mixture of several components found in complex carbohydrates: cellulose, hemicelluloses, and lignin. These substances make up the structural building materials in the plant cell wall. The other components of fiber, pectin and gums, are involved with plant cell structure and metabolism. The proportion of these fiber components varies from food to food. Fiber is divided into two basic types: soluble and insoluble. Soluble fiber dissolves in water. Good sources include beans, fruits, vegetables, oats, and barley. Soluble fiber plays a role in lowering high serum cholesterol level and reducing the risk of heart attack by binding with cholesterol-rich bile acids in the intestinal tract. When the fiber and bile are excreted, cholesterol molecules are eliminated as well. Soluble fiber also helps to regulate the body's use of sugars, slow