Carbohydrates play important roles in the human body, providing energy for growth, maintenance and daily activities. Even though carbohydrates are composed of only three elements -- carbon, hydrogen and oxygen -- there are many structural arrangements of these elements and each arrangement forms a different carbohydrate. The simple carbohydrates consist of monosaccharides and disaccharides. Complex carbohydrates include starch, fiber and glycogen.
Monosaccharides
Monosaccharides are the simplest carbohydrates and used as basic building blocks for the more complex carbohydrates. Chemically, these carbohydrates contain a chain of six carbon atoms to which hydroxyl groups, an oxygen and a hydrogen atom, are attached. There are three monosaccharides: glucose, fructose and galactose, each with its own unique arrangement of atoms that arrangement gives each monosaccharide its sweetness and solubility characteristics. Glucose is the only fuel that your body's brain and nervous system can use for energy. Fructose, found in fruits and honey is the sweetest of all sugars. Galactose is not commonly found existing free.
Disaccharides
When two monosaccharides combine, a disaccharide is formed. Examples include maltose, lactose and sucrose. Maltose is composed of two glucose molecules. Lactose is the sugar found in milk and is formed when galactose and glucose combine. Sucrose is the most common disaccharide and is composed of a molecule of glucose and a molecule of fructose.
Complex Carbohydrates
Complex carbohydrates are formed when numerous glucose molecules and sometimes other monosaccharides combine. Examples of complex carbohydrates include glycogen, starches and fibers. In plants such as rice, wheat, corn, barley and oats, glucose is stored as starch. When starch is eaten, the linkages between the monosaccharides are broken and eventually the body converts these into glucose units that are then burned for energy.There are two types of starch, amylopectin and amylose. Amylopectin contains glucose units linked in long, branched chains. Amylose contains many glucose units combined in a straight chain.
Fiber
Fiber contains chemical bonds that the body's digestive enzymes are unable to break down.The body's inability to digest fiber as it passes through the intestinal system is the reason for its laxative effect. Fibers, such as cellulose, hemicellulose, pectins, gums and mucilages, are classified according to their chemical properties. Cellulose forms the structural framework of plant tissue and is found abundantly in the cell walls of fruits, vegetables and legumes. Pectins form gels in water and thus often used as thickeners in a variety of food products. The gums and mucilages are commonly found in processed foods as stabilizers.
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