Diabetes is a disease where the body does not produce enough or properly use insulin, a hormone that allows glucose to enter cells and be used for energy. Without enough insulin, glucose builds up in the bloodstream leading to high blood glucose levels which can damage the heart, eyes, nerves, and kidneys if left untreated. There are three main types of diabetes: Type 1 where the body does not produce insulin; Type 2 where the body does not produce enough insulin or use it properly, often affecting overweight people; and gestational diabetes which occurs during pregnancy but usually disappears after.