Age-related changes in body composition of 3- to 6-year-old Japanese children

Abstract

This study was undertaken to establish an approach for the investigation of age-related changes in indices of body composition during childhood in Japan. It provides current reference values for total body fat mass (TBFM) and lean body mass (LBM) as indices of body composition in an urban population of 3- to 6-year-old Japanese children. Moreover, we assessed the age-specific patterns of body fat distribution [subcutaneous fat mass (SFM) and internal fat mass (IFM)] during childhood. Measurements of body composition by bioelectrical impedance were made in 141 boys and 139 girls, all apparently healthy, aged 3-6 years. Determinations of impedance were made using a four-terminal impedance analyzer (TP-95K; Toyo Physical, Inc., Fukuoka, Japan). LBM was calculated using the equation of Kushner et al. (1992) and Goran et al. (1993). SFM was calculated using a modification of the equation derived by Skerjl et al. (1953). IFM was calculated as the difference between TBFM and SFM. From ages 3 through 6 years, the mean LBM increased with age in boys and girls, and showed significant age differences. Between the ages of 3 and 6, the average increment in LBM was 5.1 kg in boys and 4.4 kg in girls. On average, boys gained 0.5 kg of TBFM each year, whereas girls gained 0.4 kg of TBFM each year. Furthermore, both groups gained 0.3 kg of SFM each year. Percentage body fat decreased in both genders until approximately the age of 5, and increased again slightly at the age of 6. The age-specific pattern of fat accumulation during childhood was characterized by an almost linear increase in SFM in girls, but a transient decrease in IFM in boys. We conclude that further research is required, including longitudinal assessment of body composition variables, in order to unravel the dynamics of body composition change in Japanese children.