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Comparative Study
. 2002 Jun;26(6):789-96.
doi: 10.1038/sj.ijo.0802006.

The Effect of Sex, Age and Race on Estimating Percentage Body Fat From Body Mass Index: The Heritage Family Study

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Comparative Study

The Effect of Sex, Age and Race on Estimating Percentage Body Fat From Body Mass Index: The Heritage Family Study

A S Jackson et al. Int J Obes Relat Metab Disord. .

Abstract

Objective: To study the effects of sex, age and race on the relation between body mass index (BMI) and measured percent body fat (%fat).

Design: Cross-sectional validation study of sedentary individuals.

Subjects: The Heritage Family Study cohort of 665 black and white men and women who ranged in age from 17 to 65 y.

Measurements: Body density determined from hydrostatic weighing. Percentage body fat determined with gender and race-specific, two-compartment models. BMI determined from height and weight, and sex and race in dummy coded form.

Results: Polynomial regression showed that the relationship between %fat and BMI was quadratic for both men and women. A natural log transformation of BMI adjusted for the non-linearity. Test for homogeneity of log transformed BMI and gender showed that the male-female slopes were within random variance, but the intercepts differed. For the same BMI, the %fat of females was 10.4% higher than that of males. General linear models analysis of the women's data showed that age, race and race-by-BMI interaction were independently related to %fat. The same analysis applied to the men's data showed that %fat was not just a function of BMI, but also age and age-by-BMI interaction. Multiple regression analyses provided models that defined the bias.

Conclusions: These data and results published in the literature show that BMI and %fat relationship are not independent of age and gender. These data showed a race effect for women, but not men. The failure to adjust for these sources of bias resulted in substantial differences in the proportion of subjects defined as obese by measured %fat.

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