don's report archive

by Donald B. Ardell, Ph. D.

Wellness in the Headlines
(Don's Report to the World)

Do you know your BMI or Body Mass Index? Do you know how to compute it? Most people do not know much about this index but will, soon enough, if the trend toward increased adoption of the indicator continues. (BMI is a measure of your weight in kilograms relative to your height in meters squared.) I'll summarize the nature and current utilization of BMI and then offer a recommendation for what to do with it.

I read recently that candidates for adoption of Chinese babies must have a BMI rating of 39 or lower. If they don't, hopeful parents will not pass muster with the government-run China Center of Adoption Affairs. Want to be a model in Milan or Madrid? Make sure your BMI is not below 18.5. (See Abby Ellin, "Quick, Do You Know Your B.M.I.?" New York Times, December 28, 2006.) In the latter case, also check that you are female, very young, very pretty and that your BMI is not much more that 18.5!)

If you don't know your BMI and don't want to do the math, you can simply enter your height and weight at the National Heart Lung and Blood Institute website. Presto -- there it is.

Go ahead -- check it out. I'll wait.

Surprised? Pleased? Distressed? Your rating is based on four BMI categories:  "normal" (index rating between 18.5 and 24.9), "underweight" (18.4 or below), "overweight" (between 25 to 29.9) and "obese" (30 or higher).

The key question about BMI is this: Does it do more good than harm?

Enough of the facts. Let's go subjective and have some fun. First, here is my summary of what's good about BMI.

Well, not much to write about there. 

Next, my summary of the problems with BMI:

1. It does not convey the most important information. Nearly everyone knows his/her height and weight, so having another number tied to these two basic measures does not add much to the level of self-knowledge.
   
   
2. What should be promoted is body composition, that is, the percentage of storage fat versus lean muscle tissue. This ratio is more revealing of fitness and thus health status. (Also of more value than BMI is simple hip-to-waist ratio or waist circumference, a measure of abdominal fat.)
   
   
3. BMI readings can give distorted impressions. While the most common BMI-derived statistic is probably accurate (that 66.3 percent of American adults are overweight or obese), a number of folks who are fit, such as Sylvester Stallone and Arnold Schwarzenegger, are considered obese by BMI standards).
   
   
4. Persons classed as "normal" based on BMI may have a lot of fat and be considered healthy when they are not. This was the case in about 40 studies involving approximately 250,000 people with heart disease.

Why, then, is BMI used instead of other, more accurate and meaningful measures? The answer is obvious -- because it's simple, quick and costs nothing, unlike measuring body fat. That requires an impedance device, a caliper or, good grief-an immersion tank!

Just making up a figure is simple, quick and cheap, too, but we don't do that, for this would mislead people and, as the late president Tricky Nixon would advise, "it would be wrong." Well, actually, I do just that -- I give people a good ratio after doing the pinch, but only to make everyone feel good. That is, I tell audience members at my talks that I can pinch them and accurately assess their body composition, and offer to do so. I get a lot of takers -- people line up, eager to learn their body composition. Also, this is great fun for me, as I enjoy pinching women, but I'm an equal opportunity pincher, so I pinch the men who ask, as well. Then I tell all they have good ratios, no matter how blubbery they might be. This boosts their spirits and, in my opinion, makes them more likely to keep working on their fitness routines!

I'm kidding. I don't really do that. But if I did, it would be no less useless and maybe no more pernicious than facilitating a BMI reading.

As you might guess at this point, I'm in favor of deep-sixing the whole BMI concept. The fact that BMI usually overestimates body fat in athletes and others with muscular builds and underestimates body fat in older persons and others who have lost muscle mass are reasons enough to get ride of it. That it is hard to calculate without a handy website to run the numbers is another reason to give it up. The most persuasive reason to dump the whole BMI campaign, though, is because it is subject to misuse, such as is going on in China in the example given above, not to mention all the stress being added to the lives of those cute models in Milan or Madrid.

What do YOU think about this BMI business?

Be well. Look on the bright side of life.

(Note: This essay will be filed in the archives in the PHYSICAL DOMAIN under the skill area of lifestyle habits. Additional articles related to this theme may be found there.)

(Ed. Note: Views expressed in this and other columns are those of the author and not necessarily those of the SeekWellness Editorial Board.)

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