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How Much Does Body Mass Index Really Matter?

You may have heard the phrase "body mass index" thrown about at your local fitness center. Pick up any book about exercise these days, and chances are high you will encounter a chapter that explains the ubiquitous BMI chart.

And if the chart is present, so are the warnings. "If your body mass index puts you in the overweight category, you are at greater risk of heart disease, cancer, and diabetes."

But we skinny people don't get off scot-free, either. My current BMI skinny frog hanging onto string

indicates that I am underweight. And, according to health authorities, I probably have an eating disorder, and am at higher risk of cardiac disease than people of "normal" weight.

Whatever.

The body mass index is a loose approximation of your total body fat, given your weight and height (this site has a BMI calculator, in case you're curious to find out yours). The chart looks something like this:

	BMI
Underweight	less than 18.5
Normal weight	18.5-24.9
Overweight	25-29.9
Obese	30 and over

Fit Over 40 ebook will help you get in shape, regardless of your BMI.

How useful is the body mass index?

Countless doctors use the BMI to determine whether their patients need to lose weight. Because, it is said, to be overweight is to be at risk for early disease and death.

But does it really? What about the mother of three who is overweight because she had trouble losing her pregnancy weight, but she participates in a yoga class several days a week and eats no processed food?

What about the man who developed obesity as a child, has tried several diets, and is now in the "overweight" category despite his moderate bodybuilding attempts and eating habits?

man on bathroom scale

In her book, Health at Every Size: The Surprising Truth about Your Weight, Linda Bacon points to several studies that concluded that overweight people can easily live as long as--even longer than--people of normal weight. She also states that in a U.S. study consisting of more than 170,000 adults, researchers found that "the difference between actual weight and perceived ideal weight was a better indicator of mental and physical health than BMI [emphasis mine]." ^{p. 126}

Now, please. If you think I am advocating a diet of donuts and Deluxe Cheeseburgers, think again.

However, even the medical profession admits to problems with the body mass index. For example, for bodybuilders, the BMI is apt to overestimate body fat. For older people who have lost muscle mass (the opposite of bodybuilders), the BMI is likely to underestimate the body fat.

In addition, a person can be overweight or obese and still have healthy results on the crucial portions of a physical exam: blood pressure, cholesterol level, etc. The body mass index indicates a higher risk for disease only if the BMI is at least 25 and the person has two or more of the following:

high blood pressure
high LDL (bad cholesterol)
low HDL (good cholesterol)
high triglyceride level
high blood sugar level
sedentary lifestyle
smokes cigarettes

Translation? If your BMI is, say, 28, but your blood numbers and lifestyle are in excellent shape, you will not (or should not) be asked to try to lose weight.

If that is not enough reason for you to hold the BMI in healthy skepticism, here is one more:

Belly fat is a better indicator of heart disease risk than the BMI

The December 15, 2006 issue of the American Journal of Epidemiology published a study relating waist girth to heart disease. The study found that men with the largest abdomens were 42% more likely to develop heart disease. The figure for women was 44%.

The conclusion was that abdominal fat was a better predictor for future disease than overall body fat, which is what the BMI is supposed to measure.

My conclusion? The BMI has some, albeit limited, value. In the context of a physical exam and bloodwork, it can be used to aid doctors in determining whether a patient's weight may bring on potential problems.

May I coach you? The next time you hear about the BMI being presented as the be-all and end-all indication for health, ignore it. Better yet, send the person promoting that idea to this article.

And thanks in advance. ;-)

Whether or not the BMI is valid, exercise is an important part of your life. Why not get a Workout Pass and take advantage of many online workout programs? With so many to choose from, you're sure to find one that's right for you!

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Find out how Fit Over 40 is helping many people ditch the BMI worry as they reclaim their desired level of fitness.