The overall objective of the Dietary Protein and Insulin Sensitivity Study is to test the hypothesis that increased protein in a diet with reduced carbohydrate (35% energy) can ameliorate insulin resistance in the absence of weight loss, and that this effect is independent of saturated fat content. Moreover, we will test whether such diets result in beneficial changes in total LDL cholesterol, small, dense LDL, and HDL cholesterol that are also independent of saturated fat intake.