Effects of surgically induced weight loss by Roux-en-Y gastric bypass on osteocalcin

Background: Osteocalcin (OC), a protein synthesized by osteoblasts, is a marker of bone turnover with undercarboxylated OC (ucOC) being involved in glucose homeostasis. Although laparoscopic Roux-en-Y gastric bypass (LRYGB)-induced weight loss likely alters bone turnover, data on markers of bone turnover remain less clear. The aim of this study was to examine the effect of surgically induced weight loss on OC and ucOC. Methods: A total of 32 individuals with a body mass index 50.2±10.2 kg/m² underwent LRYGB. Osteocalcin, ucOC, other blood analytes (e.g., vitamin D, leptin, total and high-molecular-weight adiponectin), and homeostasis model assessment for insulin resistance were measured before and after weight loss. The effect of an acute nutrient load on OC parameters after a mixed meal tolerance test also was assessed. Results: Six months after surgery, there was an increase in OC (17.8±7.4 [mean±SD] [baseline] versus 31.5±9.8 ng/mL [follow-up]; P<.001) and ucOC (7.3±6.2 versus 18.5±8.9 ng/mL; P<.001). Although adiponectin increased, only the magnitude of change in OC and leptin was correlated (r =-.43; P =.017). After weight loss, an acute nutrient load reduced OC (31.5±9.8 [0-hour] versus 29.6±8.2 [2-hour] ng/mL; P =.024), whereas ucOC was higher (18.8±9.3 [0-hour] versus 21.1±8.6 [2-hour] ng/mL; P<.001). Conclusion: Surgically induced weight loss was associated with increases in OC and ucOC. Underlying mechanisms are unclear, but change in OC may be related to change in leptin. After a nutrient load, the increase in ucOC suggests a potential role as a short-term compensatory regulator of glucose homeostasis.