Gastric Bypass Surgery for Morbid Obesity Leads to an Increase in Bone Turnover and a Decrease in Bone Mass

Abstract

Abstract Little is known about the effects on the skeleton of laparoscopic Roux-en-Y gastric bypass (LRGB) surgery for morbid obesity and subsequent weight loss. We compared 25 patients who had undergone LRGB 11 ± 3 months previously with 30 obese controls matched for age, gender, and menopausal status. Compared with obese controls, patients post LRGB had significantly lower weight (92 ± 16 vs. 133 ± 20 kg; P < 0.001) and body mass index (31 ± 5 vs. 48 ± 7 kg/m2; P < 0.001). Markers of bone turnover were significantly elevated in patients post LRGB compared with controls (urinary N-telopeptide cross-linked collagen type 1, 93 ± 38 vs. 24 ± 11 nmol bone collagen equivalents per mmol creatinine; and osteocalcin, 11.6 ± 3.4 vs. 7.6 ± 3.6 ng/ml; both P < 0.001). Fifteen patients were studied prospectively for an average of 9 months after LRGB. They lost 37 ± 9 kg and had a 29 ± 8% fall in body mass index (both P < 0.001). Urinary N-telopeptide cross-linked collagen type 1 increased by 174 ± 168% at 3 months (P < 0.01) and 319 ± 187% at 9 months (P < 0.01). Bone mineral density decreased significantly at the total hip (7.8 ± 4.8%; P < 0.001), trochanter (9.3 ± 5.7%; P < 0.001), and total body (1.6 ± 2.0%; P < 0.05), with significant decreases in bone mineral content at these sites. In summary, within 3 to 9 months after LRGB, morbidly obese patients have an increase in bone resorption associated with a decrease in bone mass. Additional studies are needed to examine these findings over the longer term.