A general term for dietary fibre; that part of food which cannot be digested in the gastrointestinal tract, although it can be metabolised in the colon by the micro-organisms there. Roughage falls into four groups: cellulose, hemicelluloses, lignins and pectins, found in unrefined foods such as wholemeal cereals and flour, root vegetables, nuts and fruit. It has long been known to affect bowel function, probably because of its capacity to hold water in a gel-like form. It plays an important role in the prevention of CONSTIPATION, DIVERTICULOSIS, IRRITABLE BOWEL SYNDROME (IBS), APPENDICITIS, DIABETES MELLITUS and possibly cancer of the colon (see INTESTINE).