 Surgery on the gastrointestinal GI tract results in profound changes to the metabolic profile. This is well described, including the rapid resolution of diabetes seen after bariatric surgery. The underlying pathophysiology, and incidence in lean patients undergoing surgery for cancer, is somewhat less described. The investigators plan to assess the symptomatic and glycaemic profile, as well as causative pathways, for metabolic symptoms in patients after surgery on the GI tract. The investigators will use glucose tolerance tests, physiological challenges with somatostatin analogues and antibiotics, and assess tissue transcriptomic changes. 