Gender Differences in Relationship between Fat-Free Mass Index and Fat Mass Index among Korean Children Using Body Composition Chart

PURPOSE: This study aimed to investigate gender differences in the relationship between fat-free mass index (FFMI) and fat mass index (FMI) by applying body composition chart on Korean elementary students. MATERIALS AND METHODS: Data from 965 healthy Korean children of 8 to 12 years of age (501 boys, 464 girls) were obtained. FFMI and FMI were plotted on the body composition chart, and the differences in the relationships between FFMI and FMI were separately evaluated by gender or grade. RESULTS: Weight was heavier and BMI was higher in 3rd and 4th grade boys compare to girls. The value of FFM was higher in boys, but FM was not different. In subgroup analysis by grade, significant gender by FFMI interaction (p=0.015) was found, indicating that the slope of the lines for FMI vs. FFMI was different between boys and girls (Figure was not shown). In subgroup analysis by gender, grade by FFMI interaction was significant in boys, indicating that FMI vs. FFMI relationship differed according to grade only in boys. CONCLUSION: Boys are leaner than girls, despite having similar BMI. Gender difference in the direction of the change of the FFMI and FMI relationship is evident in children.