Glucose provides energy for cells throughout the body. This simple sugar is produced through the digestion of carbohydrates (even complex carbohydrates, such as those in whole grains, must be broken down into simpler components). The body’s ability to use glucose depends on the hormone insulin, produced by the pancreas. Blood levels of glucose rise after meals, but insulin keeps glucose levels within a narrow range; excess glucose is stored in the liver as glycogen, a chain of glucose molecules, to be used when food is not available or when extra energy is needed.