1. Diabetes Mellitus type 2

2. HbA1c ≥ 5.5% and ≤ 7.0%

3. Treatment with Metformin (daily dose 500 - 3000 mg monotherapy, the past 3 months)

4. Age 30 - 65 years

1. Pre-treatment with PPAR gamma agonists or DPP IV inhibitors or GLP-1 analogues within the last three months

2. History of type 1 Diabetes Mellitus

3. No full legal mental and physical ability to give informed consent

4. Uncontrolled hypertension (systolic blood pressure > 160 mmHg and/or diastolic blood pressure > 90 mmHg)

5. Anamnestic acute and chronic infections

6. Inflammatory bowel disease and/or diabetic gastroparesis

7. Anamnestic history of epilepsy

8. Anamnestic history of hypersensitivity to the study drugs or to drugs with similar chemical structures

9. History of severe or multiple allergies

10. Treatment with any other investigational drug within 3 months before trial entry

11. Progressive fatal disease

12. History of drug or alcohol abuse in the past 2 years

13. Liver disease with ASAT or ALAT above 3 times the upper normal limit

14. Serum potassium > 5.5 mmol/L

15. Moderate to Severe Kidney disease with a GFR ≤ 60 ml/min

16. Pregnancy or breast feeding

17. Sexually active woman of childbearing potential not practicing a highly effective method of birth control as defined as those which result in a low failure rate (i.e. less than 1% per year) when used consistently and correctly such as implants, injectables, combined oral contraceptives, hormonal IUDs, sexual abstinence or vasectomised partner

18. Have had more than one unexplained episode of severe hypoglycaemia (defined as requiring assistance of another person due to disabling hypoglycaemia) within 6 months prior to screening visit

19. History of dehydration, diabetic precoma, diabetic ketoacidosis or diabetic gastroparesis

20. Acute (within the previous 2 days) or scheduled investigation with iodine containing radiopaque material

21. Acute myocardial infarction, open heart surgery or cerebral event (stroke/TIA) within the previous 6 months

22. Anamnestic uncontrolled unstable angina pectoris, pericarditis, myocarditis, endocarditis, haemodynamic relevant aortic stenosis, aortic aneurysma or heart insufficiency NYHA III or IV

23. Anamnestic recent pulmonary embolism or pulmonary insufficiency

24. Smoking within the last 6 months (> 1 cigarette/day)

25. Planned change in antidiabetic, lipid lowering or blood pressure medication