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Int J Obes Relat Metab Disord. 2002 Jun;26(6):789-96.

The effect of sex, age and race on estimating percentage body fat from body mass index: The Heritage Family Study.

Author information

1
Department of Health and Kinesiology, Texas A&M University, College Station, Texas, USA. Ajackson@mail.uh.edu

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.

PMID:
12037649
DOI:
10.1038/sj.ijo.0802006
[Indexed for MEDLINE]

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