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, 40 (4), 587-94

Prediction of Percent Body Fat Measurements in Americans 8 Years and Older

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Prediction of Percent Body Fat Measurements in Americans 8 Years and Older

J Stevens et al. Int J Obes (Lond).

Abstract

Background/objectives: Although numerous equations to predict percent body fat have been published, few have broad generalizability. The objective of this study was to develop sets of equations that are generalizable to the American population 8 years of age and older.

Subjects/methods: Dual-emission X-ray absorptiometry (DXA) assessed percent body fat from the 1999-2006 National Health and Nutrition Examination Survey (NHANES) was used as the response variable for development of 14 equations for each gender that included between 2 and 10 anthropometrics. Other candidate variables included demographics and menses. Models were developed using the Least Absolute Shrinkage and Selection Operator (LAASO) and validated in a ¼ withheld sample randomly selected from 11 884 males or 9215 females.

Results: In the final models, R(2) ranged from 0.664 to 0.845 in males and from 0.748 to 0.809 in females. R(2) was not notably improved by development of equations within, rather than across, age and ethnic groups. Systematic over or under estimation of percent body fat by age and ethnic groups was within 1 percentage point. Seven of the fourteen gender-specific models had R(2) values above 0.80 in males and 0.795 in females and exhibited low bias by age, race/ethnicity and body mass index (BMI).

Conclusions: To our knowledge, these are the first equations that have been shown to be valid and unbiased in both youth and adults in estimating DXA assessed body fat. The equations developed here are appropriate for use in multiple ethnic groups, are generalizable to the US population and provide a useful method for assessment of percent body fat in settings where methods such as DXA are not feasible.

Conflict of interest statement

CONFLICT OF INTEREST

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Differences in R2 values between equations developed in all males in the fitting sample versus equations developed in age- and race/ethnic-specific subgroups of the fitting sample (R2 all males – R2 subgroup). R2 values are for the prediction of criterion percent body fat from DXA and were calculated in age- and ethnic-specific subgroups of the validation sample using the different equations developed in the fitting sample. Letters represent results for models shown in the footnote of Table 2 with the point estimate at the center of the letter. NHANES 1999–2006.
Figure 2
Figure 2
Differences in R2 values between equations developed in all females in the fitting sample versus equations developed in age- and race/ethnic-specific subgroups of the fitting sample (R2 all females – R2 subgroup). R2 values are for the prediction of criterion percent body fat from DXA and were calculated in age- and ethnic-specific subgroups of the validation sample using the different equations developed in the fitting sample. Letters represent results for models shown in the footnote of Table 3 with the point estimate at the center of the letter. NHANES 1999–2006.
Figure 3
Figure 3
MSD between percent body fat measured by DXA compared with values predicted using BMI in the cross-validation data set within subgroups by age, ethnicity and BMI category: BMI predicted percent body fat minus percent body fat from DXA. A value above zero indicates that the equation developed in the full fitting sample had a higher R2 in the validation sample than the equation developed in boys only, and values below zero indicate that the equation developed in the full fitting sample had a lower R2 compared with the equation developed in boys only. The letters on the plot identify result from different equations with the point estimate at the center of the letter. NHANES 1999–2006.

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