Diabetes is a disease in which your blood sugar (glucose) levels are too high. You get blood sugar from the foods you eat, but a hormone called insulin usually helps you turn your blood sugar into energy for your cells.
However, with type 1 diabetes, your body does not make insulin. And, in the more common type 2 diabetes, your body does not use insulin well and eventually loses the ability to make insulin at all. Without enough insulin, your blood sugar stays in your blood.