Carbohydrates, often simply referred to as sugars, are the major source of energy for the body. Approximately half of your total caloric intake is in the form of carbohydrates. The three classes of carbohydrates include monosaccharides, oligosaccharides and polysaccharides. The majority of dietary carbohydrate is in the form of polysaccharides found in grains and vegetables. The remaining comes from the simple sugars.
Monosaccharides
Monosaccharides are structurally the simplest form of carbohydrate and are referred to as the "simple sugars." The three single unit sugars are glucose, fructose and galactose. The simple sugars do not require digestion as they are quickly absorbed in the intestines and transported to the liver for energy needs. Glucose, also known as dextrose, is the basic sugar that fuels the body for energy. Fructose is the sweetest of the simple sugars and is found primarily in fruits and honey. Galactose is generally produced from the digestion of milk sugar.
Oligosaccharides and Disaccharides
Oligosaccharides are short-chain compounds of two to 10 monosaccharide units. Of the oligosaccharides, the disaccharides are the most abundant. Disaccharides are two sugar units linked together. The three disaccharides are sucrose, lactose and maltose. Sucrose is common table sugar. Sucrose is a glucose-fructose compound made from sugar cane or sugar beets. Lactose is a glucose-galactose compound and is the only sugar not found in plants. Formed in the mammary glands, it constitutes 40 percent of milk solids and aids in the absorption of calcium and phosphorus. Maltose is a glucose-glucose compound formed in the intermediate breakdown of starch.
Polysaccharides
Polysaccharides are complex carbohydrates consisting of many single sugar units. Starch, glycogen and dietary fiber are the nutritionally important polysaccharides. Starch is the most commonly digestible polysaccharide and exists as amylose and amylopectin. Glycogen is similar in structure to starch and is the major form of stored carbohydrate in the body. Formed within the body tissue, it is vital to metabolism and energy balance.
Dietary Fiber
Several polysaccharides are considered dietary fiber because humans lack the enzyme to break these sugars down and they do not have a direct energy value. Cellulose is the major component of cell walls in plants. It is necessary in the diet for its role as a bulking agent and energy source for intestinal bacteria. Hemicellulose, pectins, gums and mucilages are other dietary fibers that absorb water and create bulk, slowing the emptying of the stomach and prevents spastic colon pressure.
References
- "Advanced Nutrition and Human Metabolism, Third Edition"; James L. Groff, Sareen S. Gropper; 1999
- "Basic Nutrition and Diet Therapy"; Sue Rodwell Williams; 2000
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