The carbohydrates are a vast and diverse group of nutrients found in most foods. This group includes simple sugars (like the sugar you add to your morning coffee) and complex forms such as starches (contained in pasta, bread, cereal, and in some fruits and vegetables), which are broken down during digestion to produce simple sugars. The main function of the simple sugars and starches in the foods we eat is to deliver calories for energy. The simple sugar glucose is required to satisfy the energy needs of the brain, whereas our muscles use glucose for short-term bouts of activity. The liver and muscles also convert small amounts of the sugar and starch that we eat into a storage form called glycogen. After a long workout, muscle glycogen stores must be replenished. Both simple sugars and starches provide about 4 calories per gram (a gram is about the weight of a paper clip). Because carbohydrates serve primarily as sources of calories (and we can get calories from other macronutrients), no specific requirement has been set for them (see Chapter 1, The Dietary Reference Intakes [DRIs], page 5). But health experts agree that we should obtain most of our calories (about 60 percent) from carbohydrates. Our individual requirements depend on age, sex, size, and activity level.
In contrast to the other carbohydrates, fiber (a substance contained in bran, fruits, vegetables, and legumes) is a type of complex carbohydrate that cannot be readily digested by our bodies. Even though it isn't digested, fiber is essential to our health. Nutrition professionals recommend 25 to 30 grams of fiber daily.
Simple sugars make foods sweet. They are small molecules found in many foods and in many forms. Some simple sugars occur naturally in foods. For example, fructose is the sugar that naturally gives some fruits their sweet flavor.
Table sugar, the sugar that we spoon onto our cereal and add to the cookies we bake, also called sucrose, is the most familiar simple sugar. A ring-shaped molecule of sucrose actually consists of a molecule of fructose chemically linked to a molecule of another simple sugar called glucose. Sugars such as fructose and glucose are known as monosaccharides, because of their single (mono) ring structure, whereas two-ringed sugars such as sucrose are known as disaccharides. Another disaccharide, lactose, the sugar that gives milk its slightly sweet taste, consists of glucose linked to yet another simple sugar called galactose. The inability to digest lactose to its constituent sugars is the cause of lactose intolerance, a condition common to adults of Asian, Mediterranean, and African ancestry.
The table sugar that we purchase is processed from sugar cane or sugar beets. As an additive to many different types of prepared or processed foods, sucrose adds nutritive value (in the form of calories only), flavor, texture, and structure, while helping to retain moisture. Today, sucrose is most often used to sweeten (nondietetic) carbonated beverages and fruit drinks (other than juice), candy, pastries, cakes, cookies, and frozen desserts. One of the most commonly consumed forms of sugar is called high-fructose corn syrup. High-fructose corn syrup is also commonly used to sweeten sodas, fruit drinks (not juices), some ice creams, and some manufactured pastries and cookies. Other forms of sucrose include brown sugar, maple syrup, molasses, and turbinado (raw) sugar.
Foods that are high in added sugar are often low in essential nutrients such as vitamins and minerals. Unfortunately, these foods are often eaten in place of more nutrient-rich foods such as fruits, vegetables, and low-fat whole-grain products, and they may prevent us from obtaining essential nutrients and lead to weight gain.
Nutritionists are concerned by the enormous increase in sugar consumption by Americans during the past 30 years, particularly because much of this sugar is in the form of soft drinks. On average, teens today drink twice as much soda as milk, and young adults drink three times as much soda as milk. As a result, their intake of calcium-rich foods is low, a factor that is thought to contribute to lower bone
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