Chapter 2. Carbohydrates

Glucose is a moderately sweet, simple sugar found in commercially prepared corn syrup and sweet fruits such as grapes and berries. It is also the chief end product of starch digestion and glycogen hydrolysis in the body. Glucose is the form of carbohydrate found circulating in the bloodstream and is the primary carbohydrate used by the body’s cells for energy. Fructose, commonly referred to as fruit sugar, is a very sweet sugar found in honey, ripe fruits, and some vegetables. It is also formed from the digestion or acid hydrolysis of the disaccharide sucrose. Galactose is not found in a free form in foods. However, it makes up 50% of the disaccharide lactose, which is present in the milk of all mammalian species. Like fructose, galactose is released during digestion. Within the body, galactose is converted to glucose by the liver and eventually enters the circulation in the form of glucose.

Disaccharides are made up of two monosaccharide units linked together. Lactose, the sugar found in the milk of all mammals, contains a molecule of glucose and a molecule of galactose. It is the only carbohydrate of animal origin that is of any significance in the diet. Sucrose, commonly recognized as table sugar, contains a molecule of glucose linked to a molecule of fructose. It is found in cane, beets, and maple syrup. Maltose is made up of two glucose molecules linked together. This disaccharide is not commonly found in most foods, but it is formed as an intermediate product in the body during the digestion of starch.

Although the exact definition of dietary fiber continues to be debated, dietary fiber (also referred to as nonstarch polysaccharides) comprises several forms of plant carbohydrate. The major carbohydrate components of dietary fiber include cellulose, hemicellulose, pectin, and the plant gums and mucilages. Lignin, a large phenylpropane polymer, is the only noncarbohydrate component of fiber. Plant fiber differs from starch and glycogen in that its monosaccharide units have a beta-configuration and are linked together by beta-bonds. These bonds resist digestion by the endogenous enzymes of the gastrointestinal tract. As a result, dietary fiber cannot be broken down by enzymes of the intestinal tract to monosaccharide units for absorption in the small intestine.

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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Carbohydrates
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