The goal of this prospective cohort study is to examine circulating biomarkers before and after weight loss in patients with obesity, with or without concomitant diabetes, undergoing bariatric surgery. The main questions that are being addressed are:

• Do biomarkers of hemostasis, including coagulation, fibrinolysis, and platelet function improve following surgery and if so, is that improvement more pronounced in patients with diabetes?
• Do biomarkers of endothelial function and other aspects of vascular function improve following surgery and if so, is that improvement more pronounced in patients with diabetes?
• Do biomarkers of inflammation, including markers of adipocyte function, improve following surgery and if so, is that improvement more pronounced in patients with diabetes?
• The possible role of circulating extracellular vesicles reflecting biological functions above will also be investigated (optional) Participants will be asked to attend in total five study visits before and after surgery including a final visit at two years post-surgery. Comparisons will be performed within- as well as between groups.

In this single centre, prospective, parallel group, cohort study, patients meeting the eligibility criteria are recruited at the department of surgery at Ersta hospital, Stockholm, Sweden. Patients with obesity and type 2 diabetes (T2D) are matched for age and sex with the group of patients with obesity without T2D. During the study the participants attend five study visits: at baseline, at the morning of surgery (after two weeks of low calory diet), 6 weeks, 1 year and 2 years after surgery. At each study visit a nurse records blood pressure, weight, height, and waist/hip circumferences. In addition, the nurse recalls the medical history and any medication use including contraceptive hormones and analgesics. Fat mass is determined using bioelectric impedance. Venous blood samples are collected with the patients in the supine position after overnight fasting and at least 20 minutes of rest. For later analyses, 25 mL of blood is collected in citrate tubes and centrifuged for 20 min at 2000 x g in room temperature. Plasma aliquots are subsequently stored at minus 80 degrees Celsius. Blood test regarding values at baseline (not the primary outcome variables) will be analysed at the local hospital laboratory. Examples of those basic variables are concentrations of glucose, insulin, blood cell counts and lipids.

Inclusion criteria:

• Age 18-70 years old
• Planned for Roux-en-y gastric bypass surgery
• Obesity fulfilling criteria for bariatric surgery (according to the European Association for the Study of Obesity guidelines, ref. Yumuk et al. European Guidelines for Obesity Management in Adults. Obes Facts 2015;8:402-42.)

Exclusion criteria:

• Ongoing treatment with anticoagulant medication
• Ongoing treatment with antiplatelet medication other than acetylsalicylic acid
• Type 1 diabetes