Brain Clock and Insulin Resistance

Inclusion Criteria: Group 1: obese people with normal insulin sensitivity * age 25-65 years * BMI\>30 * fasting plasma insulin ≤62 pmol/L * fasting plasma glucose \<5.6 mmol/L * Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) ≤ 4.5 Group 2: obese people with insulin resistance * age 25-65 years * BMI\>30 * fasting plasma insulin \>62 pmol/L * not fulfilling the American Diabetes Association (ADA) criteria for type 2 DM Group 3: obese subjects with overt type 2 DM * age 25-65 years * BMI\>30 * diagnosis type 2 DM according to ADA criteria Exclusion Criteria: * An extreme chronotype (midpoint of sleep on free days (MSFsc) before 2:00 or after 6:00). * Active psychiatric disorder (including circadian rhythm sleep disorder) as defined in Diagnostic and Statistical Manual of Mental Disorders (DSM) 5 * Disorders of the central nervous system (Early-onset dementia, stroke, epilepsy, Parkinson's disease, brain tumor) * Severe visual impairment (WHO classification) * Shift workers * Crossing \> 2 time zones in the 3 months before the study * Patients with type 2 DM receiving insulin treatment or glucagon-like peptide (GLP) 1 agonists * MRI contraindications