The state of prediabetes is characterized by an increase in insulin resistance and a decrease in pancreatic beta cell function. The prestage of type 2 diabetes mellitus can be identified by an impaired glucose tolerance and/or by an impaired fasting blood sugar. Apart from weight loss and increase in physical activity, the development of type 2 diabetes mellitus can also be prevented by dietary changes. A low-fat diet with a dietary fiber intake of more than 30g/d was shown to represent an effective preventive approach. A high-fiber diet has many positive effects on the physical health status. In addition to positive effects in the gastrointestinal tract it has an obvious potential to support weight reduction and to improve disturbances of carbohydrate and fat metabolism. At the present state of knowledge, insoluble dietary fibers as found in whole grain cereal products are considered to be especially effective in the prevention of type 2 diabetes mellitus. A high intake of fruits and vegetables as well as pulses also exerts health-promoting properties. A high-fiber diet also plays an important role in the prevention of obesity and coronary heart diseases.