The goal of this project is to understand why bariatric surgery is such an effective treatment for obesity with a focus on brain mechanisms. Cerebrospinal fluid (CSF) neuropeptide, hormone and protein levels will be measured as a surrogate for changes in brain activity in participants before and after bariatric surgery as compared with participants before and after diet-induced weight loss. The investigators are studying neuropeptides and hormones that are know to be involved with the regulation of appetite and body weight to determine if some of the changes that are expected to occur after diet-induced weight loss do not occur after bariatric surgery. In addition, proteomic analysis will be used to uncover new protein biomarkers that are unique to surgical weight loss. The results of these studies will help explain why bariatric surgery is so effective in achieving long-term weight loss. Understanding how the central nervous system responds to bariatric surgery could help the development of alternative nonsurgical therapies for obesity and its metabolic complications.