The biliopancreatic diversion and duodenal switch (BPD-DS) is an accepted and published type of bariatric surgery in the United States. The surgery involves both restriction and malabsorption to achieve weight loss by creating a sleeve gastrectomy as well as two intestinal connections that bypass some of the small intestine, decreasing the amount of food that is absorbed. The BPD-DS procedure produces the most weight loss of any bariatric surgery commonly performed but has the highest risk of malnutrition and gastrointestinal side effects. The loop duodenal switch (L-DS) is a bariatric surgery which has been modified from a biliopancreatic diversion and duodenal switch to maintain excellent weight loss while possibly reducing side effects. The surgical modifications in this procedure include reducing the number of intestinal reconnections from two to one and reducing the amount of small intestine which is bypassed. The L-DS operation is considered experimental by the American Society of Metabolic and Bariatric Surgery as long-term data in large numbers of patients is not available for weight loss or side effects. The purpose of this study is to examine weight loss and other outcomes in the L-DS operation up to 1 year after the procedure.