Metabolism and Bariatric Surgery Study

The purpose of this study is to determine if diet-induced weight loss causes different changes in hormones that control appetite and glucose control than surgery-induced weight loss. The overall research plan is a non-randomized prospective study of 3 different weight loss (WL) interventions and a lean and an obese healthy control group.

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 relapse and the lack of safe, effective and affordable therapies 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.

Weight loss with calorie restricted liquid diet. Subjects will be placed on a 800 kcal/day diet with a meal replacement (Optifast) provided by the investigator for 12 weeks. Then, transitioning to a higher calorie diet intake up to a year. Subjects will be closely monitored by study dietitian

A linear mixed effects model will be used to compare the cortisol changes between the LCD and the surgery groups. Specifically, cortisol change will be modeled as longitudinal outcome, and the main predictors are time and treatment group, and the time-treatment interaction.

Inclusion Criteria: Men and women Ages 18-65 Years Old Exclusion Criteria: Altered Sleep-wake Cycle Type 1 or 2 Diabetes Previous Bariatric Surgery Lactose Intolerance Any Special Diet restrictions. Use of medications that may affect body weight at screening or during a 3-month period prior. Untreated thyroid disease Other medical conditions like Cushing's, acromegaly, Hearth failure, Crohn's disease, etc. Pregnancy Tobacco or opioid use Alcohol dependence > 3% weight change over the 3month period prior to screening Unwillingness to maintain current level of physical activity over duration of study period