The study group consists of 200 Caucasian type 1 diabetic patients with elevated adipose tissue content as measured by electrical bioimpedance, treated at the Poznan University of Medical Sciences Department of Diabetology in 2009-2014. All patients have type 1 diabetes diagnosed by autoimmune antibodies, and are treated with intensive insulin therapy. This group is divided into metformin treated arm (group I+ M, 100 subjects), the remaining 100 patients are treated with insulin alone (control group, group I). Metformin is administered at least 6 months at a mean dose of 1000 mg/day.