BMI isn't accurate for everyone

10:11 PM, Nov 13, 2012   |    comments
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AP file photo.

MOUNT PLEASANT, Mich. (WZZM) - There's a new trend in health insurance. Many policies are now requiring participants to get a yearly exam that includes your Body Mass Index (BMI). If you're outside of the healthy range, you may end up paying a higher premium.

The BMI has been around for 150 years and is considered the gold standard for measuring body fat. It divides your height by your weight, if that number is 25 you are considered fat, over 30 obese.

But unfortunately, not everyone is being treated equally. Some people are being called fat when actually they might be some of the healthiest people in America.

Central Michigan University's Health Sciences building is probably one of the last places you expect to find fat students, but we found for twenty-something men who according to their BMI measurement are considered borderline or fat.

Dr. Jeffrey Edwards, a professor of exercise science for nearly 30 years, says the BMI isn't an accurate way to measure body fat. "The BMI isn't capable of identifying your actual body composition. It's just weight over height."

Edwards says it's a good gauge, but not an absolute measurement.  "There's no doubt we have an obesity epidemic. We're not calling into question that. The problem is can you use the BMI as a good measure of body composition for an individual and the answer is often no."

Based on the BMI measurement that 25 is considered fat and 30 obese, all four of the men had a BMI between 23 and 27, giving them a body fat percentage of 21%, Dr. Edwards says this is an excellent example of the flaw in the system.  "The problem is what we'd really like to know is how much fat you have, how much muscle you have."

So Dr. Edwards puts his students through the most accurate test for body fat composition: the underwater weighing system. It requires each student to enter the water, sit on a weighted chair, exhale the air out of their lungs and dunk their head for several seconds.  Then repeat.

The tank takes into account the amount of lung capacity and weight each individual has and measures the lean muscle mass.

The results are eye-opening.

The BMI had all of the young men at 21% body fat but in reality they range from 17.9% - 4.5%.  In fact, the one considered the fattest by BMI standards actually had the lowest percentage of body fat at 4.5%. "Matt a classic example of someone who has a lot of lean body mass, so you get hurt in the BMI formula," says Edwards.

But where it could really hurt Matt is in his wallet if his health insurance set premiums according to BMI measurements. "Well that would be terrible. I wouldn't like to go off of that system. I would be paying a lot more when I shouldn't be because I'm in great shape."

Unfortunately, it is the system of measurement that is and will continue to be used until a new system can be developed. There are lots of ideas being tested. One that seems to be the most accurate is called DEXA but it uses x-ray technology which makes it pricier.

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