On inclusion, comorbidities associated with obesity will be recorded. After recording of the informed consent patients will be randomized in two groups: usual care or intra-gastric balloon. In the latter, a second randomization will be performed between air-filled balloon or water-filled balloon. Six months later, after withdrawal of the balloon (if required), laparoscopic gastric by-pass will be performed. Thereafter, patients will be followed during 6 months.