Impact of intra- and extra-osseous soft tissue composition on changes in bone mineral density with weight loss and regain

Abstract

Recent studies report a significant gain in bone mineral density (BMD) after diet-induced weight loss. This might be explained by a measurement artefact. We therefore investigated the impact of intra- and extra-osseous soft tissue composition on bone measurements by dual X-ray absorptiometry (DXA) in a longitudinal study of diet-induced weight loss and regain in 55 women and 17 men (19-46 years, BMI 28.2-46.8kg/m2). Total and regional BMD were measured before and after 12.7±2.2 week diet-induced weight loss and 6 months after significant weight regain (30%). Hydration of fat free mass (FFM) was assessed by a 3-compartment model. Skeletal muscle (SM) mass, extra-osseous adipose tissue, and bone marrow were measured by whole body magnetic resonance imaging (MRI). Mean weight loss was 9.2 4.4kg (P<0.001) and was followed by weight regain in a subgroup of 24 subjects (6.3 2.9kg; P<0.001). With weight loss, bone marrow and extra-osseous adipose tissue decreased whereas BMD increased at the total body, lumbar spine, and the legs (women only) but decreased at the pelvis (men only, all P<0.05). The decrease in BMD pelvis correlated with the loss in visceral adipose tissue (VAT) (P <0.05). Increases in BMD legs were reversed after weight regain and inversely correlated with BMD legs decreases. No other associations between changes in BMD and intra- or extra-osseous soft tissue composition were found. In conclusion, changes in extra-osseous soft tissue composition had a minor contribution to changes in BMD with weight loss and decreases in bone marrow adipose tissue (BMAT) were not related to changes in BMD. © 2011 The Obesity Society.