Abstract
Bariatric surgery is associated with increased bone turnover. The mechanisms involved are unclear but may involve nutrition, mechanical unloading, altered secretion of gastrointestinal and adipose hormones and changes in inflammatory status leading to weight loss induced bone loss. We assessed markers of bone turnover in obese adults (F=19, M=1; BMI 46.5 + 7.9 kg/m2) following Roux-en-Y gastric bypass surgery (RYGB), and investigated their relationship to endocrine and inflammatory markers following this procedure. Bone specific alkaline phospatase (BAP) and N-teleopeptide of type I collagen (NTx) were measured as markers of bone formation and resorption, respectively. Repeated measures analysis of variance (ANOVA) was used to evaluate differences over time. Step-wise multiple regression was used to model the contributions of body weight and composition, endocrine and inflammatory markers to bone metabolism (expressed as BAP/NTX). BAP/ NTx declined significantly (p<0.05) within 1 month after surgery and remained low for 12 months post RYGB. Before surgery, glucose (partial R2 = 0.23, p=0.03) and non-esterified fatty acids (FFA) (partial R2 = 0.12, p=0.09) explained 35% of the variance in BAP/NTX (model R2 = 0.35). Twelve months after RYGB, 48% of variance in BAP/NTx was explained by glucose (partial R2 = 0.21, p=0.04), insulin (partial R2 = 0.17, p=0.05) and C-reactive protein (CRP) (partial R2 = 0.10, p=0.09; model R2 =0.48) Changes in body weight and composition were not significantly related to the BAP/NTX ratio 12 months after surgery. In conclusion, the use of BAP/NTx ratio and stepwise regression models can be used to explore the inter-relationships among bone metabolism, endocrine and inflammatory markers following RYGB weight loss induced bone loss over an extended period of persistent weight loss.