Is the New Obesity Scale Better than BMI?

Will BMI get replaced with a new body fat measurement?

Have you ever noticed how glaringly inaccurate the body mass index (BMI) can be? Telling you that you’re overweight even though you can wriggle into a size 6 pair of jeans? Yeah, me neither. But for people who have just a sliver of body fat, like my husband, it does happen. According to BMI calculators, my better half is beyond portly. Even though he can knock out 100 pushups, has a 32-inch waist and does P90X daily, his BMI of 27.5 puts him squarely into the overweight category.

Long considered a reliable measure of one’s fitness or fatness, BMI is not without its flaws. Calculated by dividing one’s weight by height, BMI can overestimate the amount of fat on extremely fit people, like hulking football players. Just because they weigh a lot in proportion to their height doesn’t mean they’re fat, but the BMI can’t make that distinction.

Experts have known for some time that the body mass index is not the best indicator of healthy weight. The challenge has been in finding a simple consumer-friendly calculation that is. Now a new study published in the journal Obesity suggests that body adiposity index, or BAI, may be the solution. BAI estimates one’s body fatness via two measurements: height and hip circumference -- meaning, you may never have to step foot on a scale again. According to the researchers who developed the tool, the ratio of hip circumference to height is strongly linked to the amount of body fat a person carries. Still, it won’t give you as precise a number as those claw-like calipers that they use to pinch your inches at the gym. But it’s a start.

Designed and tested on Mexican-Americans at the University of Southern California, Los Angeles, BAI still needs to be tried out on other populations to be sure it’s just as accurate. While it might prevent athletically built people from being classified as obese, BAI isn’t without its own limitations. For instance, critics point out that it can be difficult to obtain the correct hip circumference measurement in severely obese people. BAI also doesn’t take belly fat into consideration, even though people with an apple shape are at particular risk of heart disease, Type 2 diabetes, high cholesterol and death. Though more research is needed, this could mean that the body adiposity index won’t be as good a predictor of health risks as BMI is. Time and more research will tell.

For now, people should continue to gauge their body fitness level with the BMI calculator. The good news is that, even if the measurement doesn’t accurately assess everyone, those who it’s likely to mislabel (athletes) probably know that they’re not obese. You can use iVillage’s Beyond BMI tool to calculate your BMI, and get specific health recommendations here.

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