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Monday, April 23, 2012

Human body diversity


Body Mass Index (BMI; in kg/m2) can be used to indicate if you are overweight or normal.  But it can wrongly suggest fatness in people who are athletic or muscular. 

Ethnic differences in the relation of body mass index to morbidity and mortality have led investigators to question whether a single cut-off for obesity should be applied to all ethnic groups. According to a definition of obesity was issued by the world health organization in 1995,  "overweight" is as a bmi calculator value between 25 and 29.9 and "obesity" is a BMI value greater than or equal to 30. There are contradicted opinions whether these values can be applied on every subject, without taking into account its nationality and ethnicity.

 

The strongest argument of those who disagree with the use of the same BMI values for every race is that there are differences in body fat percentages, in different races. Wagner et al (2000) state clear that it is generally accepted that African-Americans have a higher bone mineral density and bone mineral content than whites, and that their muscle mass is higher. The same investigators suggest that “It is now generally believed that African-Americans have less visceral fat than matched (for age, BMI, circumference ratios) Caucasian Americans." Thus, the lower amount of visceral adipose tissue among American Blacks (matched for BMI) could turn out to be an artefact, as their total body-fat levels could be lower.
 
Prentice et al (2001) give several examples of non-white non-American races, that have a higher body fat percentage for a given BMI. This supports the conclusion that different races need different BMI overweight thresholds. For example, Asians range of normal BMI is lower, between 18.5 to 22.9 kg/m2, with BMI>=23.0 is considered overweight for Asians (HCA, 2000). They also suggest that Black Americans probably need a higher BMI cut-off.
 
Another argument is the body size and shape. For example, Fuller et al (1989) suggest that there are clear differences in limb length between ethnic groups. It is acceptable that bioelectrical impedance of the body is, to a large extent, determined by the impedance of the limbs. However, bioelectrical impedance is used to determine the body’s fat content. So there is possibly an error in fat determining the body composition. Additionally, Norgan (1994) supports that “Subjects with relatively long legs will have lower BMIs” (for example) the 'longleggedness' of the Australian aboriginals contributes to 2 kg/m2 to their low BMI.


Maria Toumpi | Clinical Nutritionist - Dietitian MSc
Photography by:  wafflephoto


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