Effects of Gastric Bypass and Gastric Banding on Bone Remodeling in Obese Patients With Type 2 Diabetes

Abstract

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 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.

Results: 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.

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.

Figure 1.

Mean ± SEM percentage change in weight in gastric bypass (black bar) and gastric banding (gray bar) groups. Percentage weight loss from preoperative baseline is shown at day 10 (A) and 1 year (B) after surgery. *, P < .001 for the comparison of gastric bypass vs gastric banding; #, P < .05 for the within-group comparison against baseline.

Figure 2.

Mean ± SEM percentage change in CTX and P1NP in gastric bypass (black bar) and gastric banding (gray bar) groups. Percentage change from preoperative baseline is shown for CTX and P1NP at day 10 (A and C, respectively) and 1 year (B and D, respectively) after surgery. *, P < .001 for the comparison of gastric bypass vs gastric banding; #, P < .05 for the within-group comparison against baseline.

Figure 3.

Scatterplot of percentage change in fasting CTX and PYY within the gastric bypass group at day 10 (+) and 1 year (●). Increases in CTX were directly correlated with change in fasting PYY (r = 0.70, P < .001).

Figure 4.

Mean ± SEM percentage change in postprandial CTX in gastric bypass (solid line) and gastric banding (dotted line) groups. Postprandial changes in CTX were assessed during a 2-hour MMTT at baseline (A), day 10 (B), and 1 year (C) after surgery. Although fasting CTX increased after gastric bypass, postprandial declines in CTX were more pronounced after gastric bypass than gastric banding at day 10 and 1 year (P < .001 for both).