The validity of predicted body fat percentage from body mass index and from impedance in samples of five European populations

Objectives: To test and compare the validity of a body mass index (BMI)-bas ed prediction equation and an impedance-based prediction equation for body fat percentage among various European population groups. Design: Cross-sectional observational study. Settings: The study was performed in five different European centres: Maast richt and Wageningen (The Netherlands), Milan and Rome (Italy) and Tampere (Finland), where body composition studies are routinely performed. Subjects: A total of 234 females and 182 males, aged 18 - 70 y, BMI 17.0-41 .9 kg/m(2). Methods: The reference method for body fat percentage (BF%(REF) ) was either dual-energy X-ray absorptiometry (DXA) or densitometry (underw ater weighing). Body fat percentage (BF%) was also predicted from BMI, age and sex (BF%(BMI)) or with a hand-held impedance analyser that uses in addi tion to arm impedance weight, height, age and sex as predictors (BF%(IMP)). Results: The overall mean (+/-s.e.) bias (measured minus predicted) for BF% (BMI) was 0.2 +/- 0.3 (NS) and - 0.7 +/- 0.3 (NS) in females and males, res pectively. The bias of BF%(IMP) was 0.2 +/- 0.2 (NS) and 1.0 +/- 0.4 (P < 0 .01) for females and males, respectively. There were significant difference s in biases among the centres. The biases were correlated with level of BF% and with age. After correction for differences in age and BF% between the centres the bias of BF%(BMI) was not significantly different from zero in e ach centre and was not different among the centres anymore. The bias of BF% (IMP) decreased after correction and was significant from zero and signific ant from the other centres only in males from Tampere. Generally, individua l biases can be high, leading to a considerably misclassification of obesit y. The individual misclassification was generally higher with the BMI-based prediction. Conclusions: The prediction formulas give generally good estimates of BF% o n a group level in the five population samples, except for the males from T ampere. More comparative studies should be conducted to get better insight in the generalisation of prediction methods and formulas. Individual result s and classifications have to be interpreted with caution. Descriptors: body composition; body fat percentage; body mass index; bioele ctrical impedance; international comparison, validation.