A broad category of sugars, starches, fibers and starchy vegetables that the body eventually converts to glucose, the body's primary source of energy. There are two classes of carbohydrates — simple and complex. Simple carbohydrates are the sugars, which include glucose and fructose from fruits and vegetables, sucrose from beet or cane sugar and lactose from milk. Simple carbohydrates are absorbed by the body very quickly. Complex carbohydrates include starches and fiber and are most commonly found in whole grains and legumes. Complex carbohydrates, which are generally large chains of glucose molecules, take longer to digest and provide more nutrients than simple carbohydrates.