Blood glucose (blood sugar) is your body's main source of energy It is controlled by insulin, a hormone made by the pancreas. Insulin allows your body to use glucose from the food that you eat for energy or to store glucose for future use. Insulin helps keep your glucose level from getting too high or too low. If your body doesn’t produce enough insulin, or if your cells don’t respond to insulin, you may end up having too much glucose in your blood. Over time high levels of glucose cause diabetes