Carbohydrates have the general formula (CH2O)n. The main dietary carbohydrates (Figure 10.3) are mono- and disaccharide sugars, for example fructose, glucose, lactose and sucrose, and polysaccharides, mainly starch, and these are usually the major suppliers of energy. Current recommendations from the WHO suggest that 55% of dietary energy should be in the form of carbohydrates. Most of the carbohydrates should be in the form of starch with no more than 10–15% of energy intake in the form of sugars. However, dietary fiber or roughage largely consists of cellulose, a polysaccharide that cannot be digested and absorbed, although it may be metabolized by bacteria in the large intestine . Foods rich in fiber include wholemeal cereals, flour, root vegetables, nuts and fruits. Dietary fiber stimulates peristalsis and protects against constipation and is known to reduce blood cholesterol and glucose and the incidence of colorectal cancers . Communities that consume high fiber diets have relatively low incidences of these cancers.