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Weight Loss & Diet Plans

What Your BMI Doesn’t Tell You

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WebMD Feature
Reviewed by David T. Derrer, MD

You've probably heard the term BMI (body mass index). It's based on your height and weight, and it's widely used to determine if you're in a healthy weight range. But as it turns out, BMI may not be the best way to size up your shape.

Taking a Closer Look at BMI

Calculated from a person's height and weight, BMI breaks down into four categories:

  • Underweight: BMI below 18.5
  • Normal: BMI ranging between 18.5 and 24.9
  • Overweight: BMI between 25 and 29.9
  • Obese: BMI of 30 or higher

But how useful is this number really?

"Probably for 90% or 95% of the population, BMI is just fine as a general measure of obesity," says Richard L. Atkinson, MD, a researcher and editor of the International Journal of Obesity.

But some critics take a different view. Scott Kahan, who directs the National Center for Weight and Wellness, says, "Traditionally, we define obesity by a certain cutoff on the BMI scale." But judging whether a person is obese based only on their size is old-fashioned and not terribly useful, he says.

Kahan specializes in helping people manage excess weight that can lead to health problems, including diabetes and heart disease. At his center, measuring BMI is only a starting point. He sees people who are overweight but healthy, and their BMI doesn't truly reflect their health risks.

"They're heavy. Their BMI puts them in the obesity range. And yet on every level that we look at, their health is actually quite good," he says. "Their cholesterol and blood pressure are excellent. Their blood sugar is excellent. They don't seem to have any health effects associated with their excess weight."

Although BMI is useful as a quick screening tool by a doctor or nurse, Kahan says, it's not enough to look at only that number.

BMI's Drawbacks

Your BMI doesn't reveal anything about the makeup of your body, such as how much muscle vs. fat you have. That's why conclusions based only on this number can be misleading, especially when it comes to the following:

1 | 2 | 3

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