Validation of bioelectrical impedance analysis in adolescents across different ethnic groups

Adolescent obesity is difficult to assess in multi-ethnic populations using BMI, due to variability in the BMI-fatness relationship. We aimed to describe body composition (BC), and to validate leg-leg bioelectrical impedance analysis (BIA), in adolescents from different ethnic groups using deuterium (D(2)O) as the reference method. Measurements were made of weight, height, total body water (TBW), and BIA (TANITA TBF-300) in 110 white, 170 Asian, and 102 black adolescents aged 11-15 years. TBW was converted to lean mass (LM) using assumed hydration of lean tissue. General linear models were used to compare BC by D(2)O between the ethnic groups. BC values from D(2)O were compared with TANITA values, and used to generate ethnic-specific prediction equations in the whole sample, and also in equation-generation (group 1) and cross-validation (group 2) subsamples. Ethnic variability in BMI did not reflect variability in adiposity. Asians had less LM than white and black adolescents, and less fat mass (FM) than white girls. TANITA in-built equations did not predict BC accurately across ethnic groups, with significant bias in white and Asian males, and Asian and black females. The new equation generated from the entire sample removes ethnic-specific mean biases. The group 1 equation showed no significant bias in any ethnic group when tested in group 2. We found significant variability in BC between ethnic groups that was not reflected by BMI. Manufacturers' equations are unsuitable for predicting BC in multi-ethnic populations, and our new equations are recommended.