A previous prospective study of BPD effect on type 2 diabetes patients with BMI 25-35 (DIA-CHIR) showed that T2DM is less sensitive to BPD beneficial effect in the simply overweight patients. A new prospective study was then planned with the aim to gain insight in the mechanism of action of BPD in T2DM patients in the 25-30 BMI range. Thirty patients will be submitted to BPD and compared with 10 nonoperated controls. Euglycemic-hyperinsulinemic clamp, OGTT, and mixed meal test will be performed in all subjects preoperatively, and 1 month, 1 year, and 5 years after BPD. Complete clinical and biochemical evaluations will be performed at 1, 4, 8, and 12 months, and every sixth month thereafter until the end of the fifth year.