You may be fatter than you think from your Body Mass Index, researchers say

A person who is classified as a normal weight based on the Body Mass Index may still carry enough fat in certain areas to significantly boost their risk of health problems, warns a study that suggests the BMI isn't the best tool to measure health.

The BMI tool looks at weight in relation to height and then classifies people as normal, overweight or obese. It's used by health professionals in Canada, the United States and most other developed countries.

But Dr. Deborah Marshall, a University of Calgary professor who helped write the recently released study published in the Canadian Journal of Public Health, says BMI is flawed because it doesn't measure fat in specific places.

"The primary culprit being the waist…. Sometimes we see what we call the classic pot belly," Marshall told the Calgary Homestretch on Wednesday.

"The result of that is that the average person could look fine and be classified as normal based on BMI [but] would actually be considered obese or overweight if we used a body fat measure," said Marshall, who teaches in the Cumming School of Medicine at U of C.

Those people could be at an elevated risk for heart disease, arthritis, diabetes and cancer because of their weight, but be unaware it, she said.

'Hidden epidemic on our hands'

On the other hand, an athlete who has muscle and weighs more than the scale says he should, according to his height, could be mislabelled.

"They could be classified as obese or overweight if you used BMI, but actually they have a very healthy body weight," she said.

Measuring skin folds with calipers — to take into account where a person's fat is distributed — is a more accurate assessment measure, she says.

"I really do think we need to think about how we measure body weight. We have an epidemic, essentially, on our hands. And also a hidden epidemic on our hands," Marshall said.

She says she is not suggesting the BMI system should be entirely abandoned.

"But I do think we have to reconsider how we do this. We don't measure body fat directly in any kind of routine way."

"So I guess my recommendation would be — this is pretty critical to understand these … indicators of potential obesity-related diseases."

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With files from the Calgary Homestretch