This is a prospective study of morbidly obese patients that are planned to conduct bariatric surgery. The patients included in the study will conduct a low-calorie diet for 6 days prior to the operation and be admitted to hospital for this period. On admission and after finishing the diet a number of tests will be performed: Weigh, height, oral glucose tolerance test, bioimpedance measurement, and samples of blood, urine and a biopsy of subcutaneous adipose tissue.

The study will include 14 patients planned for bariatric surgery with BMI 40-46. The patients will be admitted to hospital 8 days prior to planned surgery and conduct a diet based mostly on fluids (yogurt, soups). Estimated daily calorie intake will be 400-600 kcal.

At the day of admission and at day 7 a number of tests will be performed including blood tests, urine test and biometric measurement and a biopsy of subcutaneous adipose tissue. Weight will be measured every morning for the study period.

During the operation fatty tissue samples will be taken subcutaneous and from the omentum major.

This study is planned as a control group to another study where blood tests and subcutanous adipose tissue was sampled before and 6 days after bariatric surgery. The main aim of this study is to compare changes in adipose tissue and blood samples for patients before and 6 days after surgery to before and 6 days after a low-calorie diet.

Inclusion Criteria:

• BMI 40-46 kg/m2
• The patients must not conduct a diet before admission.
• Fasting blood glucose <-7 nmol/l

Exclusion Criteria:

• Diabetes mellitus
• Treatment with antidiabetics
• Allergy for substances in the planned study-diet