Roux-en-Y gastric bypass (RYGB) decreases appetite, caloric intake, glycemia, and body weight, all of which are maintained long term.It is controversial whether, after RYGB, patients choose to eat less high fat and sugary foods in favor of lower energy dense alternatives. Therefore the proposition to use direct measures in humans after RYGB to test the hypothesis that the selection and intake of foods varying in fat content and glycemic index, as well as the pattern of ingestion within and across meals, changes in a manner that leads to beneficial outcomes on body weight.

Roux-en-Y gastric bypass (RYGB) decreases appetite, caloric intake, glycemia, and body weight, all of which are maintained long term.It is controversial whether, after RYGB, patients choose to eat less high fat and sugary foods in favor of lower energy dense alternatives. If true, this could conceivably contribute to improved glycemia and body weight. Disparities among studies on food selection and intake are likely due to the almost complete reliance on self-reported food intake which is vulnerable to inaccuracy.This controversy can best be resolved by complementing existing findings with direct measures of target behaviour in humans. Therefore the proposition to use direct measures in humans after RYGB to test the hypothesis that the selection and intake of foods varying in fat content and glycemic index, as well as the pattern of ingestion within and across meals, changes in a manner that leads to beneficial outcomes on body weight.

Inclusion Criteria:

1. Surgical and non-surgical groups:

   A) Bariatric surgery B) Controls with no history of bariatric surgery

2. Independently mobile

3. Capacity to consent to participate

4. >18 years of age

Exclusion Criteria:

1. Pre-operatively: significant dysphagia, gastric outlet obstruction or anything that prevents subjects from eating a meal.

2. Post-operatively: significant and persistent surgical complications or anything that prevents subjects from eating a meal.

3. Systemic or gastrointestinal condition which may affect food intake or preference, including:

   i) pregnancy or ii) breast feeding.

4. Active and significant psychiatric illness including substance misuse

5. Significant cognitive or communication issues

6. Medications with documented effect on food intake or food preference

7. History of significant food allergy and certain dietary restrictions

8. History of liver disease or pancreatitis

9. History of bradyarrythmia or congestive cardiac failure group)

10. Use of medications with potential serious interactions with Octreotide

Patients with obesity attending a specialist obesity clinic and free living individuals.

24 months