Weight loss (WL) improves obesity-related co-morbidities such as type 2 diabetes mellitus (DM). Unfortunately, WL through life-style interventions has a high degree of recidivism and the paucity of safe, effective and affordable pharmacotherapy together with an increase in the prevalence of morbid obesity has led to a rise in bariatric procedures. Clinical trials in patients with DM show that improvements in glycemia vary between procedures and occur in the following order: Roux-en-Y gastric bypass (RYGB) > sleeve gastrectomy (SG) > laparoscopic adjustable gastric banding (LAGB) > medical/life-style therapy. This order mirrors the amount of WL with each intervention and is a major driver of glycemic improvement. The investigators have shown profound changes unique to RYGB and SG in levels of hormones that make up the "gut-brain" and "enteroinsular" axes. The association of some of these hormones with insulin sensitivity (IS) and glycemia independent of WL strongly suggests that glycemic improvements after surgery occur in part through pathways that are distinct from just calorie restriction. This study builds on results showing that levels of fibroblast growth factor 19 (FGF19), a protein secreted by intestinal cells, are increased after RYGB and SG but not after low calorie diet (LCD). This difference may affect hormones that control the stress response to weight loss. The investigators will explore differences in hormones of the gut that affect appetite, body weight, and stress response in healthy lean and obese individuals. Obese individuals will also be studied before and after 15% body weight loss induced by LCD, RYGB or SG, and again at 1 year after study enrollment.