Background: Morbid obesity is associated with decreased brain µ-opioid receptor availability, possibly resulting in higher food intake needed to gain pleasure from eating. This decrease seems to normalize already 6 months after bariatric surgery, but the longer-term effects have not been studied. Obesity and insulin resistance result in significantly increased brain insulin-stimulated glucose uptake, whereas in every other tissue glucose uptake is lower. One possible explanation to this could be central inflammation and activation of brain glial cells, which has been shown to occur in animal models of obesity. Obesity has also been shown to associate with increased risk of Alzheimer's disease and cognitive decline in several studies.

Aims: The first objective of this study is to both study the effects of bariatric surgery as well as compare the effects of gastric bypass and sleeve gastrectomy on food-associated pleasure, extending the follow-up period to 2 years postoperatively. The second aim is to investigate the effect of morbid obesity and weight loss on brain inflammation and gliosis and its association with increased brain insulin-stimulated glucose uptake. Furthermore, association of obesity, insulin resistance, central inflammation and neurocognitive dysfunction are evaluated.

Methods: A total of 60 morbidly obese subjects, 30 assigned for Roux-en-Y gastric bypass and 30 for sleeve gastrectomy according to routine treatment protocols will be recruited for this study. A control group of 30 healthy subjects will also be recruited. We will perform 1) structural MRI and MRS, 2) functional MRI during tasting and visual food cues, 3) PET imaging of µ-opioid receptor availability using [11C]-carfentanil, 4) PET imaging of cerebral inflammation and astrocyte activation using [11C]-PK11195, 5) measurement of whole-body and tissue insulin sensitivity by combining hyperinsulinemic, euglycemic clamp with [18F]-FDG-PET, 6) neuropsychological testing. The control group will only be studied once, whereas study procedures will be repeated for the morbidly obese before very-low calorie diet and 6, 12 and 24 months postoperatively.

Inclusion criteria:

Morbidly obese group

1. BMI 35.0-45.0 kg/m2, or BMI 32.0-45.0 kg/m2 and diagnosed diabetes
2. Age 18-60 years
3. Eligible to bariatric surgery evaluated according to normal treatment paradigm

Non-obese controls

1. BMI 18-27 kg/m2
2. Age 18-60 years
3. Fasting plasma glucose ≤6.1 mmol/L
4. Normal values in 2-hour oral glucose tolerance test

Exclusion criteria:

Morbidly obese group

1. Metal objects in the body (including pacemakers, metallic artificial valve prostheses, inner ear implants, surgical clipses, braces, foreign fragments)
2. Previous participation in PET studies
3. Pregnancy
4. Poor compliance, alcohol or drug abuse
5. Weight over 150 kg or waist circumference over 150 cm
6. Diabetes with fasting glucose levels ≥7.0 mmol/L, or treatment with insulin
7. Any chronic disease, medication or condition that could create a hazard to subject safety, endanger study procedures or interfere with the interpretation of results.

Non-obese controls

1. Metal objects in the body (including pacemakers, metallic artificial valve prostheses, inner ear implants, surgical clipses, braces, foreign fragments)
2. Previous participation in PET studies
3. Pregnancy
4. Poor compliance, alcohol or drug abuse
5. Smoking
6. History of eating disorders, drastic weight-gain or weight-loss
7. History of psychiatric disorders
8. Any chronic disease, medication or condition that could create a hazard to subject safety, endanger study procedures or interfere with the interpretation of results

Under preparation.