The evolving meaning of the body mass index

A recent news story in the Journal of the American Medical Association (JAMA) reminds me that lots of things in our lives are changing these days, not the least of which is the shape of our bodies.

Oh, my. This aging thing isn’t so easy, and that is really the message behind Rita Rubin’s timely piece about shifting body mass and muscle as we age and its implications. Although focused on women, I can attest personally that men fall into the same trap as well. That 250 pounds when you are older simply is not the same 250 pounds when you were in college. Now 250 pounds looks more like 280 — even though the scale still says 250. Go figure.

Although I may be trying to provide a little humor to the subject, the reality is it’s not humorous when it comes to our health. As we age, muscle turns to fat. In a process called “sarcopenia,” muscle begins an inexorable march to become fat, and for most of us it doesn’t make too much difference how much we try to forestall the shift. It is programmed into our bodies, and although exercise might help, Mother Nature simply doesn’t care as much about the gym and the treadmill as she used to.

There are practical implications to this process, as pointed out in the JAMA article.

Much of our routine health is predicated on maintaining a healthy weight. The most frequent measure of whether we are classified as “healthy,” overweight, or obese depends is body mass index (better known as “BMI”) which is calculated by measuring height relative to weight. It is not a perfect tool, however, for general populations purposes, it is the best tool we have.

Yes, there are exceptions. The classic example is Sylvester Stallone (among others), who had a very high BMI at his peak, however was obviously not overweight or obese. I can’t tell you how many times I have heard that excuse from someone who was obviously a bit on the paunchy side: “Oh, that’s not fat. It’s muscle! After all, I work out every day!”  (I learned as a physician to wonder whether those workouts were in the gym or walking multiple times back and forth to the fridge. However, I digress.)

What most of us probably don’t know is that BMI definitions have not always been what they are today, where 25 defines “normal” from abnormal. That line of demarcation used to be higher, however, it was reduced, and in the process shifted a lot of folks from healthy to overweight. So the target numbers are somewhat arbitrary, hopefully, backed by good population science that defines the difference — pardon the pun — based on solid scientific information.

As pointed out in the article, there is now debate once again whether the BMI numbers should be changed for post-menopausal women.

It appears that too many women who have either a “healthy” BMI or a slightly overweight BMI, in fact, are not healthy and have too much body fat as measured by more accurate techniques. If that’s the case, then an adjustment for these women might be appropriate to better define a weight relative to height that would more accurately reflect true “health.”

In other words, just because you think you are healthy doesn’t mean you are healthy. And it is possible that if the mavens of weight decide to change the BMI definitions, we could suddenly have a whole lot of folks who thought they were healthy and maintaining that proverbial “healthy body weight” suddenly facing the fact that they are not as healthy as they thought they were.

As if we didn’t already have enough things to worry about, now we have to get back on the diet and the scale. Does it ever end?

Lest you think I don’t take this matter seriously, I can speak from personal experience that weight has been one of the most persistent issues that has dogged me throughout my lifetime. And try as I might, I couldn’t reverse the inexorable reality that I observed in myself: I weighed the same as I did in college, I work out much more than I did in college. However, my body kept going in the wrong direction. Even my precious granddaughter blurted out one day recently that my belly had reached, uh, a larger size.

And, yes, even with all the exercise I am still trying to find out what my weight is going to be, and what I must achieve to reshape this torso into something more presentable. Today my weight is down 30 pounds — again — and I still have a long way to go. And if they change that BMI thing, well I will be eating cardboard for a very long time.

Kidding aside, this is a genuine issue for many of us. We want to be healthy, we want to be mobile, we would really like to reduce our blood sugar, cholesterol and blood pressure while reducing our risk of disease and even cancer. It’s not easy, as we all know. Many of us have been there time and again. And if that BMI thing moves further down the scale, it will capture many of us in its clutches, seeming to never let us go.

However, science is science, and data is data — as difficult as it may be to confront our reality. But confront reality we must if we are to make progress as a nation when it comes to our health. Right now unfortunately when it comes to body mass this country, for the most part, is headed in the wrong direction. Perhaps this type of discussion will help more of us focus on something that is in fact very important to our wellbeing: namely, our weight.

Yes, times are changing. And our bodies are changing. What is important to remember for our health is what we do about it. Maybe it’s time we change along with the times.

J. Leonard Lichtenfeld is deputy chief medical officer, American Cancer Society. He blogs at Dr. Len’s Cancer Blog.

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