Effect of Weight Loss on Bone Metabolism: Comparison of Vertical Banded Gastroplasty and Medical Intervention

Background: We studied the effects of weight loss on bone metabolism. Methods: 16 consecutive surgically-treated (14 female, 2 male) morbidly obese patients and 65 obese (53 male, 12 female) medically-treated patients were enrolled in an observational study. Surgical treatment for morbidly obese patients was vertical banded gastroplasty (VBG). Studies were performed prior to and 12 months after the start of treatment. Bone mineral density (BMD), bone turnover markers, sex steroids, calcium excretion and parathyroid hormone measurements were done at each visit. Results: Weight loss was more prominent with surgical than with medical treatments. Bone loss was also pronounced in the surgical treatment group, and occurred at the hip level only (P<0.05). Compared to previously reported studies, where the effects of malabsorptive treatments for obesity on bone metabolism were studied, calcium excretion and parathyroid hormone levels did not change after VBG or medical therapy. For both groups, bone markers indicated an increased bone turnover, evidenced by increased urinary excretion of deoxypyridinoline and serum levels of osteocalcin (P<0.05). Sex steroid measurements revealed a decrease in estradiol levels in the surgical treatment group, but not in medical treatment group. This finding was thought to be secondary to less weight loss in the medical group. Conclusion: Our data indicate that weight loss causes bone loss. The bone loss is independent of the method of weight reduction. However, the mechanism of the bone loss is not clear. It may be explained partly by reduced estradiol levels in female patients. Because the mechanisms of bone disease after weight loss remain unclear, it is difficult to determine the most effective treatment. It is important to detect osteopenia early, before fractures occur. Measuring BMD appears to be the only reliable method for screening.