Gender differences in body fat of low- and high-body-mass children: relationship with body mass index

The primary objective of this study was to determine gender differences in total body fat mass (TBFM) and body fat distribution (subcutaneous fat mass , SFM: and internal fat mass, IFM) in a cross-sectional sample of 280 child ren. Measurements of the body composition of 141 boys and 139 girls, all ap parently healthy and aged 3-6 years were made using bioelectrical impedance . Determinations of impedance were made using a four-terminal impedance ana lyzer (TP-95K; Toyo Physical, Fukuoka, Japan). Lean body mass (LBM) was cal culated using a previously published equation [Goran MI, Kaskoun MC, Carpen ter WH, Poehlman ET, Ravussin E, Fontvieikke A-M (1993) Estimating body com position of young children by using bioelectrical resistance. J Appl Physio l 75. 1776-1780]. SFM was calculated using a modification of the equation d erived by Skerjl [Skerjl B, Brozek J, Hunt EE (1953) Subcutaneous fat and a ge changes in body build and body form in women. Am J Phys Anthrop 11: 577- 580] and Davies [Davies PSW, Jones PRM, Norgan NG (1986) The distribution o f subcutaneous and internal fat in man. Ann Hum Biol 13: 189-192]. The main modifications of the equation in the present study were the introduction o f: (1) mean thickness of adipose tissue over body surface/2, and (2) skin m ass. IFM was calculated as the difference between TBFM and SFM. The body ma ss index (BMI: kg/m(2)) was calculated from the formula: body mass/height(2 ). For each gender, the subjects in the lowest and highest 25th percentiles were designated as "low body mass" and "high body mass", respectively. In the present study, no gender differences in absolute TBFM. SFM and IFM were observed in either of these groups. In contrast, gender differences in rel ative TBFM (%Fat) and SFM (SFM/mass) were evident in girls. However, the fo ur subgroups were similar in terms of relative IFM (IFM/mass). The TBFM was independently related to SFM, IFM and %Fat in both genders after adjustmen t for BMI; however, there was no significant association of SFM with IFM af ter adjustment for BMI in any group. Even after adjustment for BMI, IFM was independently related to % Fat in both genders, although SFM was not indep endently related to %Fat in any group except low-body-mass boys. This study shows that relative TBFM and SFM are higher in high-body-mass groups and t end to be higher in girls than in boys, and that the higher % Fat in high-b ody-mass girls than in high-body-mass boys appears to be associated with in ternal adipose tissue deposits. External adipose tissue mass does not appea r to be related to the higher %Fat levels in high-body-mass girls. In addit ion, subcutaneous fat mass appears to be higher in low-body-mass girls than in low-body-mass boys, although this observation needs confirmation using more valid measures of subcutaneous fat such as computerized tomography and magnetic resonance imaging.