This study aimed to generate sex-specific percentile curves for the percentage of body fat (PBF) in Thai children using a bioelectrical impedance analysis (BIA). The secondary objective of this study was to determine the association between body fat and other anthropometric measurements. A cross-sectional study was conducted on 3455 Thai school children aged 6-18 years. The body-fat contents were measured using BIA. Smoothed percentile curves of PBF were derived using a scatter plot with a smooth curve fitted by the Loess method. The correlations between the body fat and the anthropometric measurements were assessed using the Spearman's rank correlation. The 50th and lower body-fat-percentile curves of the boys slowly increased until age 12, after which they slightly decreased until age 15 and then slightly increased until age 18. In the higher boys' percentiles, the body fat sharply increased until age 11 and then decreased until age 18. In the girls, the PBF percentiles increased steadily from 6 to 18 years. The body-mass index was strongly correlated with PBF and fat mass in both sexes. The waist-to-height ratios showed strong correlations with PBF and fat mass in the boys but were moderate in the girls. The use of PBF percentile curves can be an additional metric for the evaluation of obesity in Thai children.
Keywords: adolescents; body fat; children; obesity; reference curves.