Quick Answer: Dietary fiber, or roughage, is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition and can be grouped generally by their solubility, viscosity and fermentability, which affect how fibers are processed in the body. Dietary fiber has two main subtypes: soluble and insoluble. They are components of many foods from plants, such as legumes, whole grains, cereals, vegetables, fruits, nuts, and seeds. Regularly consuming substantial dietary fiber is generally associated with supporting health and lowering the risks of several diseases. Dietary fiber consists of non-starch polysaccharides and other plant components, such as cellulose, resistant starch, resistant dextrins, inulins, lignins, chitins, pectins, beta-glucans, and oligosaccharides. Food sources of dietary fiber have traditionally been divided according to proportion of soluble vs. insoluble fiber.