Diabetes is a condition in which the body cannot properly store and use fuel for energy. The body's main fuel is a form of sugar called glucose, which comes from food (after it has been broken down). Glucose enters the blood and is used by cells for energy. To use glucose, the body needs a hormone called insulin that's made by the pancreas. Insulin is important because it allows glucose to leave the blood and enter the body's cells.
Diabetes develops when the body can't make any or enough insulin, and/or when it can't properly use the insulin it makes. For some people with diabetes, the body becomes resistant to insulin. In these cases, insulin is still produced, but the body does not respond to the effects of insulin as it should. This is called insulin resistance. Whether from not enough insulin or the inability to use insulin properly, the result is high levels of glucose in the blood, or hyperglycemia.
There are two main types of diabetes: type 1 diabetes and type 2 diabetes. About 90% of people with diabetes have type 2 diabetes, which used to be called adult onset diabetes. However, more and more children are being diagnosed with type 2 diabetes due to the rise in obesity.
Some people do not have diabetes but also do not handle glucose as well as normal. This is called impaired glucose tolerance (IGT). Up to 40% of people with IGT will eventually develop type 2 diabetes.