Carbohydrates are a group of compounds containing molecules of glucose, or sugar. There are three main forms of carbohydrates, each containing varying amounts of sugar molecules linked together in a chain containing carbon, hydrogen and oxygen. Different foods are made up of different carbohydrate structures, ranging from simple to complex. The more complex the carbohydrate structure, the more sugar molecules it contains.
Monosaccharides
Monosaccharides are the simplest form of carbohydrates and contain only one molecule of sugar. Monosaccharides include glucose, or dextrose, fructose, galactose, xylose and ribose. Monosaccharides have a very sweet taste and are rapidly absorbed into your bloodstream because of their small chemical structure. All carbohydrates absorbed in your body, no matter how simple or complex, must be broken down into a single sugar molecule of glucose. Glucose is the primary fuel source for your skeletal muscles and brain and is essential in the normal function of your body.
Disaccharides
A disaccharide is a type of carbohydrate consisting of two sugar molecules joined together through a covalent bond. Disaccharides include sucrose, or common table sugar, and lactose, the sugar found in dairy products such as milk. Sucrose is the most common disaccharide and is found in many different plants. Sucrose is comprised of one molecule of glucose and one molecule of fructose. Lactose is comprised of one molecule of galactose and one molecule of glucose.
Oligosaccharides
Oligosaccharides are medium-chain carbohydrates consisting of 2 to 10 sugar molecules linked together. There are three different types of oligosaccharides: fructooligosaccharides, or FOS, galacto-oligosaccharides, or GOS, and mannan-oligosaccharides, or MOS. FOS are found in many different vegetables and consist of short chains of fructose molecules. GOS are also found in some vegetables, consist of short chains of galactose molecules and are a primary component of fiber, since they can be only partially digested. MOS are types of carbohydrates found in yeast and are not usually used as a nutritional source of sugar.
Polysaccharides
Polysaccharides are the most complex form of carbohydrates and are therefore the most dense. Polysaccharides are made up of repeating units of either monosaccharides or disaccharides linked together to form chains of hundreds to thousands of sugar molecules. The two most common forms of polysaccharides are starch and glycogen. Starches are glucose polymers that are most commonly found in potatoes, rice, wheat and corn and are a major source of sugar in the human diet. Glycogen is the storage form of glucose in your body and is comprised of hundreds to thousands of glucose molecules linked together waiting to be used for energy by your muscles and brain.
References
- "Nutrition for Health, Fitness, and Sport"; Melvin H. Williams; 2002
- "Physiology of Sport and Exercise"; Jack Wilmore, et al.; 2004
- "Lippincott's Illustrated Reviews: Biochemistry"; Pamela C. Champe, et al.; 1994
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