Validity of foot-to-foot bio-electrical impedance analysis body composition estimates in overweight and obese children.

OBJECTIVES: To examine the validity of body composition estimates obtained using foot-to-foot bio-electrical impedance analysis (BIA) in overweight and obese children by comparison to a reference four-compartment model (4-CM). SUBJECTS/METHODS: 38 males: age (mean +/- sd) 13.6 +/- 1.3 years, body mass index 30.3 +/- 6.0 kg.m(-2) and 14 females: age 14.7 +/- 2.2 years, body mass index 32.4 +/- 5.7 kg.m(-2) participated in the study. Estimates of fat-free mass (FFM), fat mass (FM) and percentage body fat (PBF) obtained using a Tanita model TBF-310 and a 4-CM (derived from body mass, body volume, total body water and total body bone mineral measurements) were compared using bias and 95% limits of agreement (Tanita minus 4-CM estimates). RESULTS: Body composition estimates obtained with the Tanita TBF-310 were not significantly different from 4-CM assessments: for all subjects combined the bias was -0.7kg for FM, 0.7kg for FFM and -1.3% for PBF. However, the 95% limits of agreement were substantial for individual children: males, up to +/-9.3kg for FFM and FM and +/-11.0% for PBF; females, up to +/-5.5kg for FFM and FM and +/-6.5% for PBF. CONCLUSIONS: The Tanita TBF-310 foot-to-foot BIA body composition analyser with the manufacturer's prediction equations is not recommended for application to individual children who are overweight and obese although it may be of use for obtaining group mean values.