Type 2 diabetes (adult-onset diabetes) interferes with the body's ability to store energy from food. The result is high levels of blood sugar. Over time, high blood sugar levels lead to complications, such as blindness, kidney failure, and heart disease. Many people with type 2 diabetes have moderately high levels of blood sugar for years before the levels reach true diabetes levels and symptoms begin. This condition is called abnormal glucose tolerance or prediabetes. A large study showed that 2 different methods can prevent or delay the development of diabetes in people with prediabetes. The first method is an intensive diet and exercise program for weight loss. The other is a small daily dosage of a diabetes medication called metformin. Because many Americans have prediabetes, using 1 of these prevention methods in all people who might benefit would be expensive. However, caring for diabetes and its complications is also expensive. It is important to know whether the costs of diabetes prevention are worth the potential benefits.