Pancreaticoduodenectomy (PD) involves removing the head of pancreas, duodenum, common bile duct, gall bladder, and/or distal stomach. In general, the postoperative changes are thought to be moderately severe, and about 20% of these patients go on to develop new clinical diabetes. PD-related factors of glucose metabolism will include removal of half of the pancreatic endocrine tissue, exclusion of the proximal small intestine, postoperative weight loss (on average, ~8% of body weight), and removal of putative diabetogenic factor in resected neoplasm. However, effect of removal of duodenum on glucose metabolism after PD has never been studied. The investigators plan to examine this issue by comparing fasting plasma levels of insulin, fasting plasma glucose, C-peptide, HbA1C, HOMA-insulin resistance, GLP-1 response after a standard meal, and body mass index (BMI) of patients before and after PD.