An African-American friend of mine on Facebook recently jubilantly posted a link to this article about a recently-discovered problem with the BMI Index, a number widely used to determine body fat levels — whether people are underweight, healthy, overweight, or obese.

The BMI index was calculated with reference to caucasian body types. But people from different ethnic backgrounds have bodies that might be constructed slightly differently, so one BMI might not accurately determine everyone’s body fat level. A more direct measure of body fat can be found through Dual X-Ray Absorptiometry (DXA or DEXA), which measures body fat directly, rather than as an index. Here are the basics:

BMI is a formula that estimates a person’s body fat using only his/her weight and height. The result is then used to determine weight categories: 18.5 and below is considered underweight; 18.6 - 24.9 healthy; 25 - 29 overweight and 30+ obese.

“This scale was created years ago and is based on Caucasian men and women,” says Bray, “It doesn’t take into account differences in body composition between genders, race/ethnicity groups, and across the lifespan.” (link)

The good news for African Americans and bad news for Asian Indians is after the jump:

When the two results were compared, researchers found that the DXA estimate of percent fat of African American women was 1.76 percent lower for the same BMI compared to non-Hispanic white women. Since BMI is assumed to represent body fatness, an African American woman would not be considered overweight or obese until she reached a higher number than what is indicated by the current BMI standards. The opposite is the case for Hispanic, Asian and Asian-Indian woman. Their percent fat is higher by 1.65 percent, 2.65 percent and 5.98 percent, respectively. So they would be considered overweight or obese at amounts lower than what the BMI standards indicates. The results for men were similar.

In short, people who are ethnically “Asian Indian” (desi, South Asian, etc.) are on average approximately six percent more overweight than they previously might have thought.

Of course, I’m sure the study, published in the British Journal of Nutrition, probably isn’t flawless, though I don’t know the precise details of how the study was conducted. One does wonder how they’re defining “Hispanic,” since the term Hispanic refers to language rather than race/ethnicity. I also wonder whether different sub-communities within the Indian subcontinent might end up having different average body fat levels relative to BMI. (Punjabis, for instance, are often thought of as on the heavier side by comparison to other Indian ethno-linguistic groups.)

This isn’t a post designed to make everyone feel fat, though I realize it might have that effect. Rather, the point is to raise awareness about the health risks associated with obesity: South Asians are more likely to have those sorts of problems (diabetes, heart problems, and the like), so we might have more of a collective investment in focusing on that aspect of our health.