Inclusion Criteria:  A. Oesophageal adenocarcinoma group:  Planned for oesophagectomy with gastric conduit reconstruction Recurrence-free at least 12 months post-operatively Weight loss ≥10% from premorbid weight or require ongoing caloric supplementation  B. Barrett's oesophagus group:  -Barrett's oesophagus group who are under surveillance from INCEUGIN  Exclusion Criteria:  Pregnant or breastfeeding, or planning to become pregnant Unable to swallow or need frequent dilatations ("stretches") Unable to eat semisolid food Allergies or dietary intolerance Diabetes mellitus type 1 Reoccurrence of disease after surgery or are having another active form of cancer Taking medication which may impact gut hormone physiology Unstable cardiovascular disease A significant neurological condition A previous upper gastrointestinal resection A medical condition that would limit the ability to take part, that might impact certain test results or might make it unsafe for the patient to take these treatments. Difficulty reading, understanding or remembering the information we have given. Previous abdominal surgery. Treatment with GLP-1 receptor agonists or DPP-IV inhibitor or insulin