Measuring body fatness in children and young adults: comparison of bioelectric impedance analysis, total body electrical conductivity, and dual-energy X-ray absorptiometry.

OBJECTIVE: To determine the level of agreement for body fatness measurements among four body composition measurement techniques.
SUBJECTS: 99 healthy children and young adults (63 males, 36 females; ages: 5-22 y) MEASUREMENT: Bioelectrical impedance analysis (BIA), bioelectrical impedance spectroscopy (BIS), total body electrical conductivity (TOBEC), and dual-energy X-ray absorptiometry (DXA) measurements of body fat mass, and its percentage of body weight (% Fat).
RESULTS: Estimates for body fat mass and % Fat were highly correlated (r = 0.72-0.97, P < 0.001) among the four methods. However, a Bland-Altman comparison among the estimates indicated significant differences between methods. The mean differences between methods for body fat ranged from -0.30 +/- 6.7 kg to 4.2 +/- 2.7 kg. Differences for % Fat ranged from 0.8% +/- 3.5% to -9.9% +/- 5.2%. Fatness classification of an individual as normal, overweight, or obese on the basis of his/her % Fat was significantly method dependent.
CONCLUSIONS: The lack of interchangeability for fatness classification makes it difficult to ensure that similar groups of subjects can be accurately selected for the same true fat content or % Fat range when different methods are used. Furthermore, this limitation may restrict comparison of findings among different studies, such as in weight reduction, exercise, or therapy programs, when the subjects were not originally classified using the same measurement methods. That is, the reported values and changes for body fat or % Fat appear to be highly method dependent.