Patients will be randomized into 2 groups:~Group 60: Patients will undergo a Roux-en-Y gastric bypass with a Biliopancreatic limb length of 60cm~Group 100: Patients will undergo a Roux-en-Y gastric bypass with a Biliopancreatic limb length of 100cm Alimentary limb will be constant in both groups (150cm length)~Bone mineral density will be evaluated before surgery and 2 years after it, by means of X ray absorptiometry (DEXA). Changes in bone mineral density in lumbar column will be assessed.
Patients will be randomized into 2 groups:~Group 60: Patients will undergo a Roux-en-Y gastric bypass with a Biliopancreatic limb length of 60cm~Group 100: Patients will undergo a Roux-en-Y gastric bypass with a Biliopancreatic limb length of 100cm~Bone mineral density will be evaluated before surgery and 2 years after it.