<qa>  What is the role of the gut hormone axis in glucose control?The role of the gut hormone axis in glucose control is of significant interest due to its proven translational impact in diabetes management. It is also significantly altered by gastric surgery, a procedure that can lead to deleterious symptoms dumping syndrome in lean, non-diabetic patients. The investigators will study a unique cohort of young, lean patients undergoing surgery for the prevention of gastric cancer, as well as patients undergoing surgery for gastric and oesophageal cancer, to further understand the regulation and pathophysiological role of the gut hormone axis. The prophylactic patient population will be recruited from the pool of patients with a genetic mutation conferring a high lifetime risk of gastric cancer Hereditary Diffuse Gastric Cancer for whom Addenbrookes Hospital provides a national clinical service. The investigators aim to define the causative physiological pathways for dumping syndrome in this group and expand our body of knowledge of gut hormones and their role in glucose homeostasis and eating behaviour. 