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

Objective: To compare skinfold thickness measurements with bioelectrical impedance analysis (BIA) as a measure of body fat for use in a survey of children (the National Study of Health and Growth). Design: Part cross-sectional, part repeated measurement study. Setting: A junior school in Bath. Subjects: 42 boys and 33 girls aged from 9 to 11 years. Interventions: Measurements of BIA, height, weight, and triceps, biceps, subscapular and suprailiac skinfolds. Results: All measurements were highly repeatable with intraclass correlation coefficients >0.90. The level of agreement between estimates of percentage of body fat derived from prediction equations based on impedance or skinfold measurements respectively was poor: the mean difference (impedance estimate minus skinfold estimate) was 4.67% (95% range -3.47 to 12.82) for boys and 7.81% (95% range 1.27 to 14.34) tor girls. The two estimates were found to correlate highly (r = 0.83 for boys and r = 0.81 for girls) because weight, used to convert estimates of fat-free mass derived from impedance to fat mass, was highly correlated with impedance and moderately highly correlated with skinfold thicknesses. The correlations of resistance (R) and (H)2/R with skinfold thicknesses were very low. There 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 converting impedance-based estimates of total body water to fat mass are not fully developed for use in children of varying ages, estimates of body fat calculated from skinfold thickness measurements remain preferable in epidemiological studies of children's health and growth. Sponsorship: Department of Health, UK.