Changes in Body Composition Following Bariatric Surgery

Overview

Obesity is an important public health issue worldwide. In the United States, the percentage of overweight and obese adults increased from 47 and 15%, respectively, to 69 and 36% in the last 40 years. Medically supervised attempts at weight loss are fraught with failures and recidivism. Surgical approaches to this important issue are both durable and effective. The gold standard approach to the surgical treatment of obesity and the attendant medical comorbidities is the laparoscopic roux-en-y gastric bypass (RYGB) and the laparoscopic sleeve gastrectomy (LSG). The mechanisms by which these two operations work and the associated side effects are not completely understood. It is established that the RYGB induces changes in both the fatty tissue mass (FTM) and lean body mass (LBM) post-operatively. This is associated with decreases in bone mineral density, basal metabolic rate, and potentially the ability to maintain weight loss. There is only incomplete information on the influence that the LSG has on body composition. This study proposes an evaluation of the changes in body composition that occurs following these two disparate operations. Using serial measurements by the BodPod and collecting information on the patients' dietary intake, exercise habits and comorbidity resolution, this study will help to better define the influence that the LSG has on body composition. It is hypothesized that the addition of a malabsorptive component will result in increased speed weight loss and overall weight loss which will have a negative impact in the preservation of lean tissue mass for the patient. This information can then be used by bariatric surgeons to better cater the surgical procedure and post-operative plan to the patient's body make up and medical comorbidities.

Procedures * All patients will undergo a bariatric surgery. The decision to undergo weight loss surgery and the operation chosen will both occur independent of and prior to enrollment in the study. The University of Iowa is a Bariatric Center of Excellence with three active, board-certified bariatric surgeons. * Serial BodPod examinations will be performed on each patient. The BodPod is a commercially available device produced by Cosmed. It uses whole-body densitometry to determine body composition. To do this, it takes small changes in the volume of air in the BodPod chamber and records the associated changes in pressure. The pressure change typically goes unnoticed and is equivalent to the change in pressure while moving from the first floor to the second floor in an elevator. The entire process takes approximately five minutes with two minutes spent within the machine. The computer will then use mathematical formulas to calculate various body composition values. * Laboratory analysis - There is a battery of labs that are ordered in both the pre-operative and post-operative time frame. These labs are ordered independent of the patient's participation in the study. These labs are ordered to assist in the management of the patient's medical comorbidities and to assess for adequate nutritional intake. These labs will also be recorded in the research database to assist in quantifying the degree of resolution of medical comorbidities. * Queries on nutritional intake and exercise will be made at each post-operative appointment. The intake of protein is an important variable and may influence maintenance of lean tissue mass. Exercise is an important component of the post-bariatric weight loss program. This also will influence the changes in lean tissue mass.