Aim To determine the impact of being obese on whole-body (WB) BMC and BMD in a group of Egyptian adolescent girls.

Methods Study included 35 obese adolescent girls (13.5±1.8 years) with body mass index (BMI) ≥ 95^th percentile and 35 maturation-matched (14.4±1.7 years) controls with BMI 15^th - 85^th percentile for age and gender. Bone mineral areas (BMA), BMC, BMD at the WB and body composition (lean mass, fat mass and fat %) were assessed by dual-energy X-ray absorpiometry (DXA). Calculations of the BMC/height ratio and bone mineral apparent density (BMAD) were computed for the WB.

Results BMD, BMC, BMAD and BMC/height ratio were highly significant higher in obese adolescent girls compared to controls. Body weight, height, BMI, lean mass, fat mass and fat% had highly significant positive correlations with BMD, BMC, BMAD and BMC/height ratio. BMA had highly significant positive correlations only with weight, height, lean and fat mass. After adjusting for either body weight or total fat mass, BMD, BMC, BMAD, BMC/height and even BMA became highly significant higher in control than obese girls. After adjusting for total lean mass, the same was observed but the differences were only highly significant between the two groups in BMC and BMA.

Conclusion This study suggests that there is positive effect of obesity on BMC, BMD, BMAD and BMC/height ratio due to body weight, while obesity has no effect on BMA.