This study evaluates the difference in post prandial tissue glucose levels between two variation of Roux-en-Y Gastric bypass by continuous glucose monitoring.

Inclusion Criteria:

1. Patients who underwent bariatric-metabolic surgery at the Medical University of Vienna in the years 2012-2016 for the "long and narrow" pouch group
2. Patients who underwent bariatric-metabolic surgery at the Clinic of Hollabrunn in the years 2010- 2012 for the "short and wide" pouch group
3. Patients on oral medication for diabetes mellitus (for subgroup assessment)
4. Stable weight (not more than + 15kg from lowest weight postoperatively)
5. Stable BMI

Exclusion Criteria:

1. Unable to give written informed consent
2. Patients with methods other than RYGB
3. Reoperation within the observed period
4. Any intervention changing pouch size or diameter of the anastomosis after the initial operation
5. Known allergy to oral contrast agent
6. Any regular intake of medication interfering with blood glucose levels

Of each bariatric-metabolic operation we plan to include 34 patients. Of these 34 patients we plan to include also patients in each group with a diagnosed Diabetes mellitus type II at the time of operation (defined by either HbA1c >6.5 or any medication or impaired fasting blood glucose level)

1. Roux-en-y gastric bypass with long ang narrow pouch ("long pouch RYGB")
2. Roux-en-y gastric bypass with short and broad pouch ("short pouch RYGB")

Patients in the two RYGB groups will be matched for sex, age, comorbidities and BMI at the time of operation.