Carbohydrates consist of carbon, hydrogen and oxygen. Carbohydrates supply the body with a source of energy and are the building blocks of cellulose and glycogen. They also combine with other molecules to form DNA, RNA, glycolipids, glycoproteins and ATP.
Glucose, fructose, galactose and ribose are all simple carbohydrates. Muscles require glucose to grow, and organs need it to function. It is also the body's most important fuel. Fructose is found in fruits and vegetables. Galactose is found in milk, while ribose, which is part of ribonucleic acid, is found in every cell of the human body. During respiration, carbohydrates are metabolised and release energy. Carbohydrates that are not converted to energy are stored as fat.
Complex carbohydrates include starch, glycogen and cellulose. Starch is found in rice, wheat, corn, carrots and potatoes. Glycogen is found in animal muscles and livers. Both starch and glycogen are forms of stored energy. Cellulose acts as the skeleton of plants and gives them their shape. It is also a source of dietary fiber.
Simple carbohydrates yield 3.87 calories of energy per gram and are commonly associated with processed foods, including baked goods, candy and soft drinks. Complex carbohydrates yield between 3.57 and 4.12 calories of energy per gram and are commonly associated with natural, unprocessed foods.