Cellulose and lignin; indigestible substances found in many food products.
The residue of plant food left after extraction by dilute acid and alkali. The term crude fiber does not include all the undigested material, which may prove to have nutritional value to man. While cellulose, plant fibers, and other so-called non-digestible carbohydrates are not digestible by the enzymes located in the upper portion of the intestine, the intestine contains flora which can partially degrade some of these food components. This degradation provides fatty acids and other useful compounds which are then absorbed by the lower small intestine and colon.