Changes in Bone Mineral Density, Body Composition and Adiponectin Levels in Morbidly Obese Patients after Bariatric Surgery

Background  Gastric bypass surgery (GBP) is increasingly used as a treatment option in morbid obesity. Little is known about the effects of this surgery on bone mineral density (BMD) and the underlying mechanisms. To evaluate changes on BMD after GBP and its relation with changes in body composition and serum adiponectin, a longitudinal study in morbid obese subjects was conducted. Methods  Forty-two women (BMI 45.0 ± 4.3 kg/m²; 37.7 ± 9.6 years) were studied before surgery and 6 and 12 months after GBP. Percentage of body fat (%BF), fat-free mass (FFM), and BMD were measured by dual-energy X-ray absorptiometry and serum adiponectin levels by RIA. Results  Twelve months after, GBP weight was decreased by 34.4 ± 6.5% and excess weight loss was 68.2 ± 12.8%. Significant reduction (p < 0.001) in total BMD (−3.0 ± 2.1%), spine BMD (−7.4 ± 6.8%) and hip BMD (−10.5 ± 5.6%) were observed. Adiponectin concentration increased from 11.4 ± 0.7 mg/L before surgery to 15.7 ± 0.7 and 19.8 ± 1.0 at the sixth and twelfth month after GBP, respectively (p < 0.001). Thirty-seven percent of the variation in total BMD could be explained by baseline weight, initial BMD, BF reduction, and adiponectin at the twelfth month (r ² = 0.373; p < 0.001). Adiponectin at the twelfth month had a significant and positive correlation with the reduction of BMD, unrelated to baseline and variation in body composition parameters (adjusted correlation coefficient: r = 0.36). Conclusion  GBP induces a significant BMD loss related with changes in body composition, although some metabolic mediators, such as adiponectin increase, may have an independent action on BMD which deserves further study.