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.

Inclusion Criteria:

• age: 35-70 years
• diabetes duration: >5 years
• documented poor glycemic control (HbA1c =>8% despite medical treatment according to GCP)
• presence of comorbidities or complications (e.g. dyslipidemia, arterial hypertension, neuropathy, retinopathy, CVD, previous stroke or TIA, lower limb amputation)
• availability to comply with the entire follow-up

Exclusion Criteria:

• general contraindications to BPD (applies also to medical controls)
• presence of anti-islet or anti-GAD antibodies or plasma C-peptide concentration <0.5 mcg/L
• blindness
• severe concomitant medical conditions (e.g. liver cirrhosis, renal failure, collagen diseases, severe endocrinopathies)
• heart failure
• recent history (less than 12 months) of myocardial infarction, stroke or TIA
• unstable angina
• pregnancy
• previous or concomitant malignancy
• severe active inflammatory, neurologic, or cardiovascular conditions
• geographic inaccessibility
• any condition which, in the opinion of the Principal Investigator, may make risky the participation in the study or bias the results