This project will study the effects of surgery for obesity on bone metabolism and hormones that regulate appetite.

Subjects will be recruited from the outpatient obesity and surgical clinics at Columbia-Presbyterian Medical Center after they have chosen to undergo a surgical procedure. The groups will not be randomized. Rather, they will decide on their choice of surgery along with their physicians. The patients will be evaluated pre-operatively and followed post-operatively for 5 years.

Initial evaluation will include a complete history and physical examination, measurement of calcium, parathyroid hormone (PTH) and vitamin D, and assessment of skeletal health using markers of bone turnover and bone mineral density.

Inclusion criteria:

1. Adult male or female > 18 years of age
2. Scheduled to undergo bariatric surgery

Exclusion criteria:

1. Vitamin D deficiency
2. Primary hyperparathyroidism
3. Treatment with lithium or thiazide diuretics which may alter PTH levels
4. Osteomalacia
5. Untreated hyperthyroidism, liver disease, Cushing's syndrome, rheumatoid arthritis, myeloma or Paget's disease
6. Impaired renal function (serum creatinine >2.0mg/dl) or history of renal osteodystrophy
7. Use of any anti-obesity medications for over 2 weeks 90 days prior to study
8. Participation in any research study 90 days prior to study
9. Any malabsorption syndromes such as celiac sprue
10. Previous bariatric surgery

Subjects will be recruited from the outpatient obesity and surgical clinics at Columbia-Presbyterian Medical Center after they have chosen to undergo a surgical procedure.