Carbohydrates are the chief source of energy for all body functions and muscular exertion. They are necessary for the digestion and assimilation of other foods. They help regulate protein and fat metabolism, and fats require carbohydrates to be broken down in the liver.
Carbohydrates are carbon, hydrogen, and oxygen molecules arranged structurally in the form of rings. Simple carbohydrates like glucose, fructose (fruit sugar), and galactose (milk sugar) are composed of one single ring and are called monosaccharides.
Sucrose from sugar cane and sugar beets, maltose (which is a component of grains), and lactose (in milk) are composed of two rings linked together and are called disaccharides. The two rings in sucrose are made up of glucose plus fructose; maltose is glucose plus glucose; and lactose is glucose plus galactose. When individuals are said to be lactose- intolerant, it means that they lack the enzyme necessary to break the disaccharide links into a monosaccharide, an action necessary for further metabolism. Fiber is a carbohydrate but consists of very large molecules that are resistant to enzymatic action.