Title of article:

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

Authors: Deurenberg P, Andreoli A, Borg P, Kukkonen-Harjula K, de Lorenzo A, van Marken Lichtenbelt WD, Testolin G, Vigano R, Vollaard N.
Journal: Eur J Clin Nutr, Nov 2001;55(11):973-9

Abstract

OBJECTIVES: To test and compare the validity of a body mass index (BMI)-based 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: Maastricht 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 (underwater 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 addition 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, respectively. 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 differences 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 each centre and was not different among the centres anymore. The bias of BF%(IMP) decreased after correction and was significant from zero and significant from the other centres only in males from Tampere. Generally, individual biases can be high, leading to a considerable misclassification of obesity. The individual misclassification was generally higher with the BMI-based prediction. CONCLUSIONS: The prediction formulas give generally good estimates of BF% on a group level in the five population samples, except for the males from Tampere. More comparative studies should be conducted to get better insight in the generalisation of prediction methods and formulas. Individual results and classifications have to be interpreted with caution.

Comments and Key points

They defined obesity, based on body fat percentages, 25% in men and 35% in women. The 35% number for women is a little higher than other articles, but they justify it by stating that it treats men and women equally:

" 7% of the females and 8% of the males would be falsely classified as obese with the BMI-based formula. These figures are 4 and 5% for the impedance-based formula".

This justification is excellent. Other studies have tended to treat men and women unequally, by having vastly different specificity between genders. It is also noteworthy that 7% and 8% false positives is equivalent to 93% and 92% specificity, which supports my own belief that Body Composition criteria should have high specificity rather than high sensitivity.

This quote is confusing:

" Generally, the BMI-based formula tends to underestimate BF% in younger subjects and overestimate it in older subjects. The impedence based formula tends to do the opposite".

I'm surprised about that. Usually, at a BMI criteria of 25 kg/m2, young people have more muscle and less fat, and older people have more fat and less muscle.

But bottom-line, this study concludes that current Body Mass Index overweight and obesity criteria are satisfactory for European caucasians.

Review & comments by Steven B. Halls, MD, Last edited 23-June, 2008, Copyright.
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