Submitted to: International Journal of Obesity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 7, 2000
Publication Date: N/A
Interpretive Summary: Accurate methods are needed to measure body composition of children. In this study measurements of fat mass (FM), fat-free mass (FFM) and percent body fat (%fat)by six different methods were compared in 101 prepubertal girls. Normal-weight, multi-ethnic, 8-y-old girls were enrolled. Body composition was measured in each child by skinfold thickness, dual-energy x-ray absorptiometry (DXA), total body potassium (TBK), total body water (TBW), multifrequency bioelectrical impedance spectroscopy (BIS), and total body electrical conductivity (TOBEC). We found significant differences between methods, with TOBEC and skinfold thickness yielding the lowest values, followed by DXA, TBK, TBW, and BIS. A methods comparison revealed that the methods are not interchangeable for FM, FFM, or %fat. Clinically significant mean differences were observed between methods, for example, the mean difference between TOBEC and BIS 2.90 kg FM, or between TOBEC and BIS 10.5%fat. In conclusion, we found that estimates of body composition i prepubertal girls are method dependent, and that the six methods studied are not directly interchangeable.
Technical Abstract: Objective: To compare estimates of fat mass (FM), fat-free mass (FFM) and percent body fat (%fat) by six different methods in prepubertal girls. Design: Cross-sectional study. Subjects: Normal-weight, multi-ethnic, prepubertal girls (age=8.5+/-0.4 years, n=101). Measurements: Body composition was measured in each child by anthropometry (skinfold thickness susing Slaughter equation), dual-energy x-ray absorptiometry (DXA), total body potassium (TBK), isotope dilution for total body water measurement (TBW), multifrequency bioelectrical impedance spectroscopy (BIS), and total body electrical conductivity (TOBEC). Results: TOBEC and skinfold thickness yielded the lowest values of FM followed by DXA, TBK, TBW, and BIS, with BIS giving the highest value of FM. All methods were significantly different for FFM, FM, and %fat (P<0.001), except FFM by DXA and TBK. The Bland-Altman limits of agreement among the methods reveal that they are not tdirectly interchangeable for FM, FFM, or %fat. The largest mean difference for FM was between TOBEC and BIS (-2.90 kg), whereas the smallest mean difference was between TOBEC and skinfold thickness (-0.14 kg). For FFM, the largest mean difference was also between TOBEC and BIS (2.83 kg), but the smallest mean difference for FFM was between DXA and TBK (-0.03 kg). For %fat, the mean differences were larger: -10.5% for TOBEC and BIS and +9.7% for skinfold thickness and BIS. The closest two techniques for %fat were TOBEC and skinfold thickness (mean difference of -0.62%) and DXA and TBK (-1.81%). Conclusions: We found that estimates of body composition in prepubertal 8 yr old girls are highly method dependent, and that the six methods studied (DXA, TBK, TBW, TOBEC, BIS, and anthropometry) are not directly interchangeable.