Objective:To analyze the current status of body composition and development patterns of children and adolescents aged 6-17 years in Guangzhou.Methods:This was a cross-sectional study involving 8 169 school students from 3 elementary schools and 3 middle schools in Guangzhou from March to December 2019.The fat-free mass (FFM) and fat mass (FM) were measured by the bioelectrical impedance analysis.The fat-free mass index (FFMI) and fat mass index (FMI) were calculated via the height standardization. T test was used to compare quantitative variables between groups.The growth pattern of body composition was described using the Hattori chart. Results:A total of 4 431 boys (54.24%) and 3 738 girls (45.76%) were involved in this study.FFM and FM both increased with age between boys and girls.Except for boys aged 11 years, FFM in boys were significantly higher than that in girls with the same age (all P<0.05). In the age of 7-10 years, FM in boys were significantly higher than that in girls with the same age, while it was significantly higher in girls aged 12 years and older than that of boys at the same age (all P<0.05). The Hattori chart showed that the difference in body composition between genders occurred after 11 years old.In contrast to girls, increases in the weight and body mass index (BMI) in boys were mainly attributed to the FFM development. Conclusions:The development of FFM and FM in children and adolescents varies with age, accompanied with the gender-specific features.FFM in boys is higher than that of girls at the same age.The weight gain in boys is mainly attributed to the development of fat-free tissues, and thus the utility of BMI may lead to the overestimation of obesity.

Objective: To compare bioelectrical impedance analysis (BIA) and dual energy X ray absorptiometry (DXA) for measuring body mineral content (BMC) of children and adolescents, and to provide a basis for BIA to accurately measure BMC in children and adolescents. Methods: By using the convenience sampling method, among 1 469 children and adolescents aged 7-17 were recruited in Guangzhou from April to May 2019, the BMC was measured by DXA and BIA. The intraclass correlation coefficient ( ICC ) and Bland Altman analysis were used to evaluate the agreement between BIA and DXA. Bland Altman analysis was performed on log transformed data. The BMC was categorized into age and specific tertiles, and the agreement between methods was evaluated based on the kappa coefficients. Treating the BMC with DXA as the dependent variable, a prediction model was constructed for correcting the BIA measure. Results: The ICC s were 0.93 and 0.94 for boys and girls, respectively. In Bland Altman analysis, the limits of agreements for the BIA to DXA ratio were wide in boys and girls, ranging from 0.27-0.76 and 0.17-0.72, respectively. The kappa coefficients for categorized BMC levels were 0.57 and 0.45 for boys and girls, respectively, showing a fair to good degree of agreement. When sub grouped by BMI, the kappa coefficients for all BMI groups of boys and overweight girls were all >0.75 , with an excellent agreement. The prediction models for boys and girls were as follows: BMC DXA =-0.51+0.44× BMC BIA + 0.06× Age +0.02× BMI ; and BMC DXA =-0.55+0.43× BMC BIA +0.06× Age +0.02× BMI , respectively. The R 2 for models of boys and girls were 0.87 and 0.87, respectively. Conclusion The agreement between BIA and DXA was poor for measuring BMC, but acceptable when evaluating the categorized BMC levels, suggesting the BIA may be applied in assessment of the BMC levels when compared to the age and gender specific population. Additionally, the prediction model for correcting BMC by BIA fis well to the measurement by DXA.