Obesity prevalence rapidly increased in the past decades in French population with multiple health consequences responsible for excess mortality. In the same period of time, the number of bariatric procedures have developed exponentially. Despite its great efficacy on weight loss but also on resolution of comorbidities, bariatric surgery is not without risks. Our hypothesis is that a better understanding of the physio-pathological consequences of obesity and bariatric surgery, notably on the gastrointestinal tract, may allow to improve the treatment of obesity and to find alternatives to bariatric surgery. The main objective of this cohort study is to systematize the collection and the conservation of biological samples (blood, stomach, liver, intestine, adipose tissue) obtained during bariatric surgery, in obese subjects undergoing surgery (including sleeve gastrectomy, Roux-en-Y gastric bypass, or revisional intervention for complication or weight regain) in the University Hospital group of Paris Nord Val de Seine (HYPNVS). The main projects that will build on this cohort will cover the physiopathology of obesity and its consequences, notably in the field of gastrointestinal tract including: modification of gastro-intestinal plasticity in severe obesity and after bariatric surgery and alterations of absorption of nutriments (lipids, proteins, carbohydrates) induced by obesity and bariatric surgery. The inclusion in this project of obese subjects before surgery, or lean or obese subjects after surgery will allow to distinguish the impact of weight loss and surgery on gastrointestinal remodeling. This cohort will also allow to characterize stomach and intestinal proteome in severe obesity and to precise the influence of tissue inflammation on metabolic disorders associated with obesity.