Title of article:

Population differences in body composition in relation to the body mass index.

Authors: Norgan NG.
Journal: Eur J Clin Nutr, Nov 1994;48 Suppl 3:S10-25; discussion S26-7

Abstract

This paper examines the relationships between body mass index (BMI) and body composition in different population groups where low BMIs might be expected to occur and assesses the extent to which BMIs are influenced by size and shape. The relationship between BMI and fat as a percentage of body weight is approximately linear although theoretically a curvilinear relationship is to be expected. However, by allowing for a variable composition of weight differences, an approximately linear theoretical relationship is obtained. There are few direct data (e.g. from densitometry, hydrometry etc.) on body composition in the groups in question and to examine the relationships indirect data were used. The regression coefficients of fat-free mass on BMI for 285 samples of Africans, people of Asian origin, Indo-Mediterraneans and Pacific people were not significantly different in the various groups of each sex; % fat on BMI was similarly related in four groups of women. Intercept terms were all significantly different. Using the sitting height-to-stature ratio (SH/S) as an index of body shape in 158 groups, the regression coefficient of BMI on SH/S was 0.90 kg/m2 per 0.01 SH/S. Mean SH/S lies between 0.50 and 0.55 in most populations so that shape could affect BMI by 5 kg/m2 and influence markedly the interpretation of BMI. However, allowing for SH/S is not straightforward as there is as much variation within as between groups. In conclusion, low BMI approximates to low weight, fat mass and fat-free mass. There are differences in the relationships of BMI to body composition but over the range 20-25 kg/m2 these may not be important in epidemiological studies. To interpret BMI in terms of body composition in more detail it is necessary to take into account sex, age, shape and ethnicity.

Comments and Key points

This article has data concerning the body fat percentages of non-European rural persons from several different regions of the world. Unfortunately, it's quite difficult to learn anything really specific or definitive from their article. For example, the graph below shows % body fat versus Body mass index, but the lines are too hard to read for individual nationalities.

Their overall conclusion was that the differences are not significant. It is also noteworthy, that the body fat percentages are fairly similar to North Americans, (just slightly lower) at equivalent BMI levels. Don't believe me? I superimposed the above graphs, onto the Heritage study¹ of North Americans, and now you see the lines are almost right on, very close to Americans.

In case you are having trouble reading the chart, the "African" data is from south of the Sahara. The "Indo-Mediterranean" data is Indian sub-continent, middle east and Lapps, but not other Europeans. The "Asian" data is mainly North, Central and South Americans but with 9 samples of Chinese and Japanese. The "Pacific" peoples, excluded Hawaiians. They got their data by a big literature search. All were non-urban peoples.

References

1. Jackson AS, Stanforth PR, Gagnon J, et al. The effect of sex, age and race on estimating percentage body fat from body mass index: the Heritage Family Study. Int J Obes Relat Metab Disord, Jun 2002;26(6):789-96

Review & comments by Steven B. Halls, MD, Last modified: 23-June, 2008, Copyright.
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