After a baseline evaluation of clinical (blood pressure, body weight, abdominal circumference) and routine laboratory parameters, renal hemodynamics [glomerular filtration rate (GFR) and renal plasma flow (RPF) assessed by iohexol and PAH plasma clearances, respectively, and filtration fraction (FF) and renal vascular resistance (RVR) calculated by standard formulas], insulin sensitivity (estimated by euglycemic-hyperinsulinemic clamp), full lipid profile assessments, and urinary albumin excretion rate (mean of three measurements in three consecutive overnight urine collections), patients satisfying the selection criteria will be randomly allocated to either the CR intervention (25% CR) or an "ad libitum" diet (AL) for 6 months. The dietary guidelines for the calorie restricted diet will be based on the measurement of the individual food-intake diary and "resting metabolic rate" (RMR) (measured using indirect calorimetry) at baseline. CR will correspond to a calorie decrease by 25% as calculated from the baseline calorie intake measured with a 7-days food-intake diary and "RMR x activity levels" (activity levels will be calculated using the physical activity questionnaire). A food-intake diary will be provided with specific instruction by the Investigator (in written form). Baseline evaluations will be repeated every three months until the end of the study (except the renal hemodynamics studies and the euglycemic-hyperinsulinemic clamp that will be repeated only at month 6).