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The value for carbohydrate content of foods given in compositional tables usually is ''carbohydrate by difference," i.e., the residual weight after subtracting amounts of water, protein, fat, and ash found by analysis; this moiety includes sugars, starches, fiber, and small amounts of other organic compounds.

DIGESTIBLE CARBOHYDRATES

In the United States, the average intake of carbohydrates by adults was 287 g for males (USDA, 1986) and 177 g for females in 1985 (USDA, 1987). Of the carbohydrates in individual diets, an average of 41% comes from grain products and 23% comes from fruits and vegetables (Anderson, 1982; Wotecki et al., 1982). About half of the total digestible carbohydrate intake is made up of monosaccharides and disaccharides. These are found in fruits (sucrose, glucose, fructose, pentoses) and milk (lactose). Sugars in soft drinks, candies, jams, jellies, and sweet desserts are mainly sucrose and high-fructose corn syrup. Complex carbohydrates, which constitute the other half of digestible carbohydrate intake, are starches found predominantly in cereal grains and their products (flour, bread, rice, corn, oats, and barley), potatoes, legumes, and a few other vegetables.

Sugars and starches together are the major source of energy in the diet. In 1985, they provided an average of 45.3% of the energy in the diet of adult men in the United States (USDA, 1986). The corresponding figures for adult women and children 1 to 5 years of age were 46.4 and 52.0%, respectively (USDA, 1987). Eleven percent of the total energy intake, representing almost one-quarter of total carbohydrate intake, is provided by added sweeteners, mostly sucrose and high-fructose corn syrup (Glinsmann et al., 1986).

Fructose intake in the United States increased after the introduction of high-fructose corn syrup into the food supply in 1970. The product is formed by the enzymatic conversion of some of the glucose in cornstarch to fructose. Its fructose content ranges from 40% to almost 100%. In 1985, high-fructose corn syrup accounted for 30% of the total sweetener supply in the United States (Glinsmann et al., 1986; IFT, 1986). In soft drinks, for example, the use of sucrose has been almost completely abandoned in favor of a high-fructose corn syrup product containing 55% fructose, approximately 40% glucose, and about 5% other sugars (Bailey et al., 1988; GAO, 1984). It is unknown whether this increased intake of free fructose has any health consequences (Reiser and Hallfrisch, 1987).

Sugar alcohols, except for xylitol, occur naturally in fruits. Because these sweet substances are slowly and incompletely absorbed from