Diabetes happens when the body lacks insulin or because the body is not working effectively, according to Dr. Jennifer Loh, chief of the department of endocrinology for Kaiser Permanente in Hawaii. The disorder can be linked to many causes, including obesity, diet and family history, said Dr. Alyson Myers of Northwell Health in New York. "To diagnose diabetes, we do an oral glucose-tolerance test with fasting," Myers said. Cells may develop a tolerance to insulin, making it necessary for the pancreas to produce and release more insulin to lower your Blood sugar levels by the required amount. Eventually, the body can fail to produce enough insulin to keep up with the sugar coming into the body.