Summary of Chapter 3 - Carbohydrates Carbohydrate is the body’s preferred energy source. Six simple sugars are important in nutrition: the three monosaccharides (glucose, fructose, and galactose) and the three disaccharides (sucrose, lactose, and maltose). The three disaccharides are pairs of monosaccharides; each contains glucose paired with one of the three monosaccharides. The polysaccharides (chains of monosaccharides) are glycogen, starches, and dietary fibers. Both glycogen and starch are storage forms of glucose—glycogen in the body and starch in plants—and both yield energy for human use. The dietary fibers also contain glucose (and other monosaccharides), but their bonds cannot be broken by human digestive enzymes, so they yield little, if any, energy. Sugars pose no major health threat except for an increased risk of dental caries. Excessive sugar intakes may displace needed nutrients and fiber and may contribute to obesity. A person deciding to limit daily sugar intake should recognize that not all sugars need to be restricted, just concentrated sweets with added sugars, which are high in kcalories and relatively lacking in other nutrients. Sugars that occur naturally in fruits, vegetables, and milk are acceptable. Two types of alternative sweeteners are sugar alcohols and artificial sweeteners. Sugar alcohols are carbohydrates, but they yield slightly less energy than sucrose. Sugar alcohols do not contribute to dental caries. The artificial sweeteners are not carbohydrates and yield no energy. Like the sugar alcohols, artificial sweeteners do not promote tooth decay. A diet rich in starches and dietary fibers helps prevent heart disease, diabetes, GI disorders, and possibly some types of cancer. It also supports efforts to manage body weight. For these reasons, recommendations urge people to eat plenty of whole grains, vegetables, legumes, and fruits—enough to provide 45 to 65 percent of the daily energy from carbohydrate. Grains, vegetables, fruits, and legumes contribute dietary fiber to the diet and, like milk, also contribute energy-yielding starches and dilute sugars. Food labels list grams of total carbohydrate and also provide separate listings of grams of fiber and sugar.
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