Fibre

Fibre a term for the undigestible constituents of food. Among the most important of these is what is called roughage. This term is almost synonymous with fibre but refers particularly to undigestible carbohydrate material, for example cellulose, in plant foods. The bran in cereals is roughage.

Roughage passes through the system unchanged, but absorbs and holds water, so acts as a laxative (see digestion). Delivering roughage in palatable form was one of the successes of some types of breakfast cereal (though many failed to do it at all). The importance of roughage to regularity in the digestive process, and comparison of its relative beneficence as opposed to the ravages wreaked (as some thought) by processed foods, underlay much of the thinking of the modern vegetarian movement and that of supporters of whole wheat breads and other whole foods (see vegetarianism; bread).