Key points from this article relating body mass index to body fat
Here’s the most basic data from that article, which I found helpful.
| Gender | Ethnicity | Mean BMI | Body Fat % |
|---|---|---|---|
| Male | White |
25.2
|
19.6%
|
| Black |
26.3
|
22.0%
|
|
| Asian |
23.3
|
21.3%
|
|
| Puerto Rican |
27.4
|
24.8%
|
|
| Female | White |
23.3
|
30.8%
|
| Black |
28.5
|
38.2%
|
|
| Asian |
22.0
|
31.9%
|
|
| Puerto Rican |
29.4
|
40.2%
|
Each race/ethinic group has a different ratio of body fat to body mass index.
Here’s how I interpreted these values, to compare races to each other. I used the Deurenberg formula relating body mass index to body fat percent, and calculated the BMI necessary to reach a body fat percentage of 25% for men and 33% for women.
The estimated BMI levels which would yield these body fat percentage thresholds were:
| Gender | Ethnicity | estimated BMI |
Body Fat % threshold |
|---|---|---|---|
| Male | White |
29.7
|
25.0%
|
| Black |
28.8
|
25.0%
|
|
| Asian |
26.4
|
25.0%
|
|
| Puerto Rican |
27.6
|
25.0%
|
|
| Female | White |
25.1
|
33.0%
|
| Black |
24.2
|
33.0%
|
|
| Asian |
22.9
|
33.0%
|
|
| Puerto Rican |
23.4
|
33.0%
|
Interjecting a sidebar comment here: Body fat thresholds of 25% and 33% are just as arbitrary as the BMI of 25 threshold. It’s like the “Who’s on first Sketch”. Who, What, Who What? Lots of studies assumed these as starting points, then compared other things to them, like this study, comparing estimated BMI to these arbitrary body fat thresholds. Or, like the Star Trek sketch using the Liar’s paradox, ‘I am a liar. I am lying. All studies that compare something to an arbitrary thing, while claiming the arbitrary thing is the true proven value, are weak science. (resuming main discussion now…)
In other words, Asians reach the body fat definition of obesity at a much lower BMI than Caucasians, and this seems to be true for the other non-white races, to a lesser extent.
But for blacks, this result seems to contradict other published reports. Kleerekoper et al suggested that blacks have less fat and more muscle1 than whites at the same BMI, but Gallagher et al didn’t find a significant difference2, after controlling for leg length ( blacks generally having longer legs than whites).
References
- Kleerekoper M, Nelson DA, Peterson EL, et al. Body composition and gonadal steriods in older white and black women. J Clin Endocrinol Metab 1994; 79:775-779.
- Gallagher D, Visser M, Sepulveda D et al. How useful is BMI for comparison of body fatness across age, sex and ethnic groups. Am J Epidemiol 1996; 143:228-239.
- Deurenberg P, Yap M Staveren WA. Body mass index and percent body fat: a meta analysis among different ethnic groups. Int J Obes Relat Metab Disord 1998; 22:1264-71
