The secondary criteria of judgement is: the differences in pre-operative weight loss between the 2 groups, number of complications occurring during the 30 days after surgery, differences in different scales of quality of life (SF36, IWQOL-lite), differences in operative time, length of hospital stay, readmissions, and medical cots between the two strategies. Efficacy and tolerance of each type of balloon (air-filled or water-filled) will be compared in the intra-gastric balloon group.