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. Diet and exercise can prevent or delay the development of type 2 diabetes in people with prediabetes. However, no definitive studies have shown whether healthy behaviors also reduce type 2 diabetes in people without prediabetes.