dietary fiber, a generic term for nondigestible carbohydrate substances found in plant cell walls and surrounding cellular material, each with a different effect on the various GI functions, such as colon transit time, water absorption, and lipid metabolism. Dietary fiber may be water soluble or insoluble. The soluble fibers include pectins, gums, mucilages, and algal products. They affect nutrient absorption and regulation. The insoluble fibers include cellulose, hemicellulose, and lignin and promote stool bulk and caloric motility. The main dietary fiber components are cellulose, lignin, hemicellulose, pectin, and plant gums. Foods high in dietary fiber are fruits; green, leafy vegetables, such as lettuce, spinach, celery, and cabbage; root vegetables, such as carrots, turnips, and potatoes; legumes; and whole-grain cereals and breads. The risk of development of constipation, hemorrhoids, diverticular disease, and colon cancer may be decreased by regular consumption of sufficient amounts of fiber. Most experts recommend intake of 20 to 30 g per day. Also called bulk, roughage.
