Gender differences in the relationship between percent body fat (%BF) and body mass index (BMI) in Japanese children.

The purpose of the present study was to examine whether gender differences exist in the relationship between percent body fat (%BF) and body mass index (BMI) in Japanese children using a population-based cohort. Subjects are comprised of 187 boys and 163 girls aged 9-10, and 137 boys and 155 girls aged 12-13. Percent BF was measured using a bipedal biometrical impedance analysis (BIA) device. The relationship between %BF and BMI was investigated as a function of age and gender with Pearson's correlation coefficient. Strong linear relationships existed between %BF and BMI, especially in girls (9-10-year-old boys: r=0.779, P<0.0001; 9-10-year-old girls: r=0.975, P<0.0001; 12-13-year-old boys: r=0.786, P<0.0001; 12-13-year-old girls: r=0.975, P<0.000l). These results indicate that %BF can be predicted from BMI in Japanese children aged 9-10 and 12-13 years. The correlations in boys were not as strong as those observed in girls, that is, less variability was explained for girls than for boys. Further study will be necessary to ascertain whether the strong correlation seen among girls will be observed in different age or ethnic groups, and to ascertain the mechanism that produces this gender difference.