MEASURING BODY FATNESS IN CHILDREN AND YOUNG-ADULTS - COMPARISON OF BIOELECTRIC IMPEDANCE ANALYSIS, TOTAL-BODY ELECTRICAL-CONDUCTIVITY, ANDDUAL-ENERGY X-RAY ABSORPTIOMETRY

OBJECTIVE: To determine the level of agreement for body fatness measur ements among four body composition measurement techniques. SUBJECTS: 9 9 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 (TOBE C), and dual-energy X-ray absorptiometry (DXA) measurements of body fa t mass, and its percentage of body weight (%Fat). RESULTS: Estimates f or 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 t o 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 depend ent. CONCLUSIONS: The lack of interchangeability for fatness classific ation makes it difficult to ensure that similar groups of subjects can be accurately selected for the same true fat content or %Fat range wh en different methods are used. Furthermore, this limitation may restri ct comparison of findings among different studies, such as in weight r eduction, exercise, or therapy programs, when the subjects were not or iginally classified using tbe same measurement methods. That is, the r eported values and changes for body fat or %Fat appear to be highly me thod dependent.