 Improvements to treatment strategies for patients upper gastrointestinal cancers have produced an increasing population of people who remain free from disease recurrence in the long term. Weight loss and nutritional problems are common among patients who attain long-term remission and cure after surgery for upper gastrointestinal cancers. However, the mechanisms underlying these problems are not well understood. In this study the investigators aim to determine whether reduced food intake after upper gastrointestinal surgery is caused by early satiety related to exaggerated post-prandial gut hormone responses. 