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.

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

Ancillary investigation of a prospective study at 2 academic institutions.

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

Serum C-terminal telopeptide (CTX), procollagen type 1 N-terminal propeptide (P1NP), and 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.

Fasting CTX increased 10 days after RYGB but not LAGB (+69 ± 23% vs +12±12%, P < .001), despite comparable weight loss at that time. By 1 year, fasting CTX and P1NP increased more after RYGB than LAGB (CTX +221 ± 60% vs +15 ± 6%, P<0.001; P1NP +93 ± 25% vs −9 ± 10%, P < .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 postoperatively.

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.