CONTEXT: Roux-en-Y gastric bypass (RYGB) leads to high-turnover bone loss, but little is known about skeletal effects of laparoscopic adjustable gastric banding (LAGB) or mechanisms underlying bone loss after bariatric surgery.

OBJECTIVE: To evaluate effects of RYGB and LAGB on fasting and postprandial indices of bone remodeling.

DESIGN AND SETTING: Ancillary investigation of a prospective study at 2 academic institutions.

PARTICIPANTS: Obese adults aged 21-65 years with type 2 diabetes who underwent RYGB (n=11) or LAGB (n=8).

OUTCOMES: Serum C-terminal telopeptide (CTX), procollagen type 1 (P1NP), and parathyroid hormone (PTH) were measured during a mixed meal tolerance test at baseline, 10 days and 1 year after surgery. Changes in 25-hydroxyvitamin D, polypeptide YY (PYY), glucagon-like peptide-1, glucose-dependent insulinotropic peptide, and insulin were also assessed.

RESULTS: Fasting CTX increased 10 days after RYGB but not LAGB (+69±23% versus +12±12%, P<0.001), despite comparable weight loss at that time. By 1 year, fasting CTX and P1NP increased more after RYGB than LAGB (CTX +221±60% versus +15±6%, P<0.001; P1NP +93±25% versus -9±10%, P<0.001) and weight loss was greater with RYGB. Changes in CTX were independent of PTH and 25-hydroxyvitamin D but were associated with increases in fasting PYY. Postprandial suppression of CTX was more pronounced after RYGB than LAGB at 10 days and 1 year post-operatively.

CONCLUSIONS: RYGB is accompanied by early increases in fasting indices of bone remodeling, independent of weight loss or changes in PTH or 25-hydroxyvitamin D. LAGB did not affect bone markers. PYY and other enterohormonal signals may play a role in RYGB-specific skeletal changes.