ESTIMATION IN COMMUNITY SURVEYS OF TOTAL-BODY FAT OF CHILDREN USING BIOELECTRICAL-IMPEDANCE OR SKINFOLD THICKNESS MEASUREMENTS

Objective: To compare skinfold thickness measurements with bioelectric al impedance analysis (BIA) as a measure of body fat for use in a surv ey of children (the National Study of Health and Growth). Design: Part cross-sectional, part repeated measurement study. Setting: A junior s chool in Bath. Subjects: 42 boys and 33 girls aged from 9 to 11 years. Interventions: Measurements of BIA, height, weight, and triceps, bice ps, subscapular and suprailiac skinfolds. Results: All measurements we re highly repeatable with intraclass correlation coefficients >0.90. T he level of agreement between estimates of percentage of body fat deri ved from prediction equations based on impedance or skinfold measureme nts respectively was poor: the mean difference (impedance estimate min us skinfold estimate) was 4.67% (95% range -3.47 to 12.82) for boys an d 7.81% (95% range 1.27 to 14.34) tor girls. The two estimates were fo und to correlate highly (r = 0.83 for boys and r = 0.81 for girls) bec ause weight, used to convert estimates of fat-free mass derived from i mpedance to fat mass, was highly correlated with impedance and moderat ely highly correlated with skinfold thicknesses. The correlations of r esistance (R) and (H)2/R with skinfold thicknesses were very low. Ther e was a moderate correlation of R and H-2/R with log(weight-for-height index), but lower than that of log(weight-for-height index) with each of the skinfolds. Conclusions: As currently available equations for c onverting impedance-based estimates of total body water to fat mass ar e not fully developed for use in children of varying ages, estimates o f body fat calculated from skinfold thickness measurements remain pref erable in epidemiological studies of children's health and growth. Spo nsorship: Department of Health, UK.