Insulin promotes the clearance of sugars from the blood into skeletal muscle and fat cells for use as energy; it also promotes storage of excess nutrients as fat. Type 2 diabetes occurs when the cells of the body become resistant to the effects of insulin, and this causes high blood sugar and contributes to a build-up of fat in muscle, pancreas, liver, and the heart. Understanding how insulin resistance occurs will pave the way for new therapies aimed at preventing and treating type 2 diabetes.