In a previous study investigating the effects of intermittent fasting, our research group found evidence for higher glucose excursions and a reduced insulin response after a 36 hour fasting period as compared to an overnight fasting period in healthy subjects.

The aim of this research project is to investigate the effect of short and midterm fasting (12 hours versus 36 hours) on glucose metabolism, glucose regulatory hormones, insulin secretion and resting energy expenditure in healthy and obese people as well as in patients with type 2 diabetes.

In this clinical study, we want to examine the effects of different fasting periods (12 hours versus 36 hours) on blood sugar levels and other metabolic parameters and hormones. For this the following investigations are carried out:

• Oral glucose tolerance test with detailed laboratory evaluation
• Bio-impedance measurement to determine body composition (muscle and fat mass)

The examinations are carried out on 4 different cohorts (normal healthy persons, obese patients, patients with type 2 diabetes and patients with type 1 diabetes).

Gender: Both, male and female Minimum Age: 18 years

Inclusion Criteria Cohort I (Healthy, non-obese subjects) Age >18 years; body mass index in the range of 20.0-27.0 kg/m2; fasting plasma glucose <110mg/dL

Inclusion criteria cohort II (Obese subjects) Age >18 years; body mass index >30 kg/m2; fasting plasma glucose <110mg/dL

Inclusion Criteria Cohort III (Cohort with subjects with Type 2 Diabetes Mellitus) Age >18 years; established Diabetes mellitus type 2 on either diet or a monotherapy or combination of metformin, Dipeptidylpeptidase (DPP)-4-inhibitors or sulfonylurea

Inclusion Criteria Cohort IV (Cohort with subjects with Type 1 Diabetes Mellitus) Age >18 years; diagnosed with Type 1 Diabetes Mellitus >12 months; treated with multiple daily Insulin injectioins (MDII) or continuous subcutaneous Insulin Infusion (CSII); stable Insulin therapy as clinically assessed by the study physician; C-Peptide negative defined as 0.3 nmol/L; HbA1c <9.5%; no diabetic ketoacidosis within the last 12 months; no severe hypoglycaemia requiring external assistance within the last 12 months; running on the FreeStyle Libre 1 (Abbott, USA) intermittently-viewed continuous Glucose Monitoring System (iCGM) as Standard of care for Glucose monitoring

Exclusion Criteria (for all participants) History of cardiovascular disease; acute or chronic inflammatory disorder; heavy drinking (more than 15 drinks/week); dietary restrictions (e.g. vegetarianism and vegan); insulin Treatment (excluded subjects with Type 1 Diabetes Mellitus); corticosteroid therapy; known malignancy; women who are pregnant, breast-feeding or trying to become pregnant; history of any chronic disease process that could interfere with interpretation of study results; therapy with antidepressants within past 6 months