[Characteristics of fat mass distribution in children aged 3-17 years in China].

<b>Objective:</b> To describe the distribution of fat mass (FM), fat mass percentage (FMP), and fat mass index (FMI) in children aged 3-17 years in China. <b>Methods:</b> Data of this study were from the National Nutrition and Health Systematic Survey in 0-18 years old children in China. A total of 70 853 children aged 3-17 years old selected from seven regions of China were included in this analysis. Body composition were measured by using bioelectrical impedance meter. The region, gender and age specific FM, FMP and FMI of the subjects were described by using <i>M</i> (<i>Q</i>₁,<i>Q</i>₃). Kruskal-Wallis <i>H</i> rank sum test was used for the comparison of intergroup differences. DSCF method was used for pairwise comparisons. <b>Results:</b> The medians of FM, FMP and FMI were 3.0 kg, 18.3% and 2.9 kg/m² in boys aged 3 years and 2.9 kg, 19.0% and 2.9 kg/m² in girls aged 3 years, respectively. The FM increased with age and the FMP and FMI decreased with age in both boys and girls aged 3-5 years. After 11 years old, the FM, FMP and FMI decreased first and then increased in boys. From 6-17 years old, the FM, FMP and FMI increased gradually in girls. The FM, FMP and FMI were higher in girls than in boys after 12 years old (all <i>P</i><0.05). The FM, FMP and FMI were relatively higher in children at the age of 6-14 in northeastern and northern China than in other regions. <b>Conclusions:</b> The age specific FM, FMP and FMI had different changing characteristics in boys and girls aged 3-17 years in seven regions of China. The FM, FMP and FMI also differed with region.