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How Accurate Is Body Mass Index, or BMI?

Is BMI still the best way to measure fatness? Some experts aren't so sure.

The Measurement of Choice continued...

Take for example, basketball player Michael Jordan: ''When he was in his prime, his BMI was 27-29, classifying him as overweight, yet his waist size was less than 30,'' says Michael Roizen, MD. 

That's one reason some experts think waist circumference can be a better overall health measurement than BMI.

Another is that your health is not only affected by excess body fat, but also by where the fat is located.  Some people gain weight in their abdominal regions (the so-called ''apple'' body shape.) Others are ''pear-shaped,'' with excess weight around the hips and buttocks. People with apple shapes are at higher risk for health problems associated with being overweight.

''Fat around your waist is more biologically active and can do more damage to your body than weight around your hips," says Roizen, co-author of You: On a Diet. "The data show that waist circumference is more reliable and more closely correlated with diseases associated with obesity.''

According to the National Institutes of Health, a bigger waist circumference (greater than 40 inches for men and 35 inches for women) is linked to a higher risk of type 2 diabetes, high blood pressure, abnormal cholesterol levels, and heart disease when BMI is 25 to 34.9.

To properly measure your waist, no math is needed. Just use a soft tape measure around your bare midsection at your belly button. Find your upper hip bone, and measure around the abdomen above the bone. The tape should be snug, but not dig into your skin.

Nonas argues that waist circumference is not a better tool than the BMI ''because we do not have good criteria or cut points for levels of overweight, obesity, age or height.'' She also thinks that properly measuring the waistline is a little more difficult than measuring height and weight.

One thing that experts agree on is that weight is only one factor in our risk for disease. When it comes to evaluating weight and its impact on health, your percentage of body fat, waist circumference, BMI, and physical activity patterns are all important.

The National Heart, Lung, and Blood Institute recommends that health care providers assess BMI, waist circumference, and any other risk factors for obesity-related conditions. Combining all of the information provides the best assessment.

What Can You Do?

The first step toward shrinking your waistline and getting your BMI in line is to start eating a healthier diet and getting regular exercise. Preventing any further weight gain and slowly reducing weight into a healthier range is an excellent goal. 

And while you might want to lose more, dropping as little as 5%-10% of your body weight can bring dramatic improvements in blood pressure, blood cholesterol, and blood sugar. 

Nonas recommends four steps to a healthy lifestyle:

  • Being physically active.
  • Making healthy food choices.
  • Avoiding overeating.
  • Scheduling an annual physical examination.

''These are the vital parts to maintaining a long and healthy life,'' she says.

Reviewed on February 12, 2008

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