Fibre is a term for the undigestible parts of food, of which roughage is the most important. Roughage and fibre are almost the same thing, but fibre refers mainly to undigestible carbohydrates in plants, especially cellulose. Whereas roughage refers just to the undigestible parts of grains and cereals, for example bran.
Roughage passes through the digestive system without being changed by the body, but it absorbs water as it passes through, so acts as a laxative. Without fibre in the diet, the digestive system slows down and constipation and other bowel disorders result. Such irritable bowel problems are typical of those with diets that contain too little fibre.
- Davidson, A. (1999) The Oxford Companion to Food, Oxford University Press. ISBN 0192115790.