This study will examine the effects of a dietary fiber on insulin sensitivity in overweight and obese women. The fiber will be added to snack foods and women will consume the foods for four weeks. In one four-week period, 15 g of fiber will be added, and 30 g will added in another period. In a third period, no fiber will be added to the snack foods. Insulin senstivity will be measured at the end of each treatment period.