Background:​ Most obese women with low-trauma fractures present normal areal bone mineral density (aBMD), suggesting that other bone parameters are more determinant for fracture risk in these patients.

Objectives:​ (i) Determine the effects of obesity in young women on areal bone mineral density (aBMD), bone geometry, strength, and volumetric BMD determined by advanced DXA-based methods;​ (ii) model the profiles of bone parameters for each population with age;​ and (iii) determine the factors related to body composition (i.e. lean tissue mass and fat mass) potentially implicated in the “bone adaptation” in the femoral region.

Subjects and methods:​ Two hundred and twenty adolescent and young women from 18 to 35 years old were enrolled in this study:​ 128 patients with obesity and 92 age-matched (±6 months) normal-weight controls. aBMD was determined with DXA, whereas hip geometry and strength parameters were assessed by hip structural analysis (HSA) and volumetric BMD by 3D-SHAPER® software.

Results:​ Compared with controls, subjects with obesity presented significantly higher aBMD at all bone sites, but the difference was greater at hip compared with lumbar spine or radius. Bone size estimates (i.e. cortical thickness), as well as strength estimates (i.e. cross-sectional area) were higher at all femoral subregions including femoral neck, intertrochanteric region and femoral shaft in young women with obesity. In whole proximal femur and all femoral compartments, vBMD was also higher in subjects with obesity, but the difference between groups was greater for cortical vBMD compared with trabecular vBMD. When hip bone parameters were modelled for each group from individual values, maximal values were reached between 20 and 26 years in both groups but, whatever the age, subjects with obesity presented higher values than controls. In both groups, lean body mass (LBM) was the parameter most positively associated with the greatest number of bone parameters studied.

Conclusion:​ Our study confirmed that young women with obesity presented higher aBMD, better hip geometry and greater strength compared with normal-weight controls. Additionally, cortical and trabecular compartments measured by 3D-SHAPER® were favourably and concomitantly modified. However, it remains to be demonstrated whether the evaluation of these new parameters would provide better prediction of fracture risk in this population than aBMD.