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the digestive tract and are less cariogenic than many other sugars, sugar alcohols such as sorbitol are useful in products intended for special diets and are often found in dietetic candies and chewing gum. In some people, however, sugar alcohols create a laxative effect due to their slow and incomplete absorption. Consumption of products containing an ounce or more of sorbitol, for example, may result in soft stools and diarrhea (IFT, 1986).

Pathophysiological Significance

Glucose absorbed in the intestine or produced by the liver is an important energy source for most tissues. Other dietary hexoses (fructose and the galactose moiety of the disaccharide lactose) are converted to glucose in the liver. Most amino acids, the glycerol component of fat, and some organic acids can be converted to glucose. Therefore, there is no absolute dietary requirement for carbohydrates, at least under most circumstances. In the absence of dietary carbohydrates, however, lipolysis of stored triglycerides and the oxidation of fatty acids increase and ketone bodies accumulate. A carbohydrate-free diet also is generally associated with an accelerated breakdown of dietary and tissue protein, loss of cations (especially sodium), and dehydration. These effects produced by low-carbohydrate diets or by fasting can be prevented by the daily ingestion of 50 to 100 g of carbohydrates (Calloway, 1971). Because of the desirability of limiting the intake of fat (see Chapter 5) and perhaps of protein (Chapter 6), the subcommittee recommends that more than half the energy requirement beyond infancy be provided by carbohydrates. One gram of carbohydrate yields 4 kcal. Thus, for people consuming as little as 2,000 kcal/day, the recommended intake would be at least 250 g. Similar recommendations, which emphasize an increased intake of complex carbohydrates rather than added sugars, have been made by other groups (see NRC, 1989).

Sugars, including sucrose in foods, provide the substrate for the microorganisms in the mouth that are responsible for tooth decay, particularly in children. Caries-producing potential depends on the ability of the carbohydrates to adhere to the tooth surface and the frequency of consumption, both of which affect the length of time carbohydrates are available as a bacterial substrate. Ingestion of other foods may inhibit the increase in oral hydrogen ion concentration associated with ingestion of sucrose and, hence, its cariogenicity. Thus, snacks of candies and other sweets may be more cariogenic than sugars consumed as part of a meal. An adequate intake of fluoride also inhibits tooth decay produced by dietary sugars.