Background There is a possibility that excess body fat affects bone mass gain and may compromise skeletal health in obese children. The purpose of the study was to identify the relationship between bone mineral density (BMD) and body composition in normal weight, overweight and obese children. Methods This was a cross-sectional study of 6- to 11-year-old children who attended the hospital's outpatient clinic. They were apparently healthy and had no history of prematurity, low birth weight, or chronic diseases. Body mass index (BMI) was used to identify subjects as normal weight, overweight or obese. BMD and body composition were assessed by dual energy X–ray absorptiometry. The BMD values (total and lumbar spine) were compared between normal weight, overweight and obese children. Correlation coefficients were calculated, and multivariate models were performed. Results Forty-nine children were included: 16 with normal weight, 15 that were overweight and 18 with obesity; the mean age was 8.4 ± 1.7 years. All the participants had a normal BMD (> – 2 SD). BMD was higher in obese children and had a positive correlation with total and trunk lean mass in the three study groups (p < 0.001). In obese children, an inverse correlation of lumbar spine BMD (Z score) with total and trunk fat mass (p < 0.05) was identified. In the multivariate models (with the whole group), the total lean mass was the only significant variable that explained BMD variability. Conclusions BMD in obese children was higher than that in normal weight children, which is explained by their greater lean mass and not by excess body fat. In obese children, a higher fat mass was related to a lower lumbar spine BMD. Lean mass had a direct correlation with BMD in the three study groups and was the most important predictor of BMD, reflecting the importance of strengthening the muscular system through performing physical activity and practicing a healthy lifestyle.

Objectives Examine the differences in bone mineral density between normal-weight children and children with overewight or obesity and its association with body composition. Methods In a cross-sectional study, 49 healthy schoolchildren from 6 to 11 years of age attending the outpatient clinic of the Hospital were included. Weight and height were measured for the calculation of the body mass index for age and height for age. The diagnosis of normal-weight, overweight and obesity was made according to the criteria of the World Health Organization. Bone mineral density (BMD) was obtained by dual energy X-ray absorptiometry (DXA). Statistic analysis. The ANOVA test was used to compare mean values between groups. Pearson's correlation to analyze the relationship between BMD and body composition; and multiple regression models to identify associated variables. Results Mean age 8.4 ± 1.7 years; 16 with normal weight, 15 overweight and 18 with obesity. All children had a normal BMD (&gt;–2 Z score). BMD (g/cm2 and Z score) was higher in children with obesity (p &lt; 0.05). Bone mineral content (BMC [g]) and BMD (g/cm2) had a positive correlation with total lean and trunk mass in the three groups (p &lt; 0.001). Fat mass correlated with BMC and BMD in children with normal-weight and overweight, but not in obese children. In multivariate models, total lean mass was the only significant variable within the model that explained the variability of BMD (g/cm2). Conclusions BMD was higher in children with obesity. Lean mass was its most important predictor, which suggests the importance of maintaining the muscular system through the practice of physical activity and healthy lifestyles. Funding Sources Universidad de Guadalajara; Hospital Civil de Guadalajara; Consejo Nacional de Ciencia y Tecnología de México.