Diabetes mellitus (commonly referred to as diabetes) is a disease of the pancreas, an organ behind your stomach that produces the hormone insulin. Insulin helps the body use food for energy. When a person has diabetes, the pancreas either cannot produce enough insulin, uses the insulin incorrectly, or both. Insulin works together with glucose (sugar) in the bloodstream to help it enter the body's cells to be burned for energy. If the insulin isn't functioning properly, glucose cannot enter the cells. This causes glucose levels in the blood to rise, creating a condition of high blood sugar or diabetes, and leaving the cells without fuel.