November 21, 2007

The Complexity of Weight and Health

I've criticised BMI in the past as an over-simplification. I don't think it handles muscle weight or bone density properly, though these concerns mainly effect athletes and the elderly.

It's common to hear people lament how low "normal" weight seems. I spend much of my time on the cusp of overweight for my height -- just above "normal". Even when I'm eight pounds above my current weight, people tell me that I don't look overweight. Visual perception is very misleading. The right or wrong clothes can change a visual assessment entirely. But I also suspect that people are used to seeing more overweight people, so I look normal in a wide range of clothes.

We turn to BMI because the weight issue is so complex, even though BMI is imperfect.

The question of what is normal weight became even more complicated when researchers started looking into how weight affects death rate and found that overweight people have a different set of problems from normal, obese and thin people, but that overweight people seemed to live longer on average than normal people.

This sort of finding is like throwing a box of crullers into the middle of an Over-eaters Anonymous meeting.  Maggie pointed me to this interesting article in the NYT that discusses some of this new controversial research.

As with many things in science and nature, the answer about what is a healthy weight is complicated, and there are a host of differing opinions. It's not only life expectancy, and not only the risk for certain diseases.

While they addressed the question of possibly changing our understanding "overweight," I was disappointed that this NYT story glossed over how they have, in the past, decided where to set the BMI categories.


Maggie also sent me this test for having or developing type 2 diabetes based on weight, height and other factors.

My risk comes out to 0 on a scale of 0-10. If I gained 15 pounds I'd be at a risk of 5. And in 5 years I'll pretty much be stuck at "5" no matter what I do about my weight.

But, clearly, they don't think that being a little bit overweight is a problem. The story changes when it's no longer "a little bit."

Cost / Benefits

I've never exercised in the hope that it would unnaturally extend my lifespan. My interest has always been to feel better, and this payoff is one that comes soon enough once you are regularly exercising that I don't have to just hope that my exercise is paying off. I have impossible-to-ignore every-day benefits from being in better shape. It's worth the brief time I have to put in exercising. The eating is harder, but thinking about the benefits is one motivator.

One example: poker. Poker requires your brain to be working right. I notice a definite difference in my poker playing when I'm in better shape. Maybe it's partly attributable to discipline alone, but there is a difference, and I believe it to be physical. Your brain, after all, is a part of your physical body. Why shouldn't it work better when your body is working better.

Basically, if you do something with your body, it works better when your body's working better. It's not rocket science, but science is about proving these things rather than just going with what sounds good.

And there is evidence that it's physical exercise, not mental exercises like "Nintendo Brain Age" or Sudoku puzzles, which will keep your mind more generally nimble into your later years.

What To Do?

I liked the comment from the first NYT article I referenced:

Dr. Gail, though, had some advice, which, he said, is his personal opinion as a physician and researcher: “If you are in the pink and feeling well and getting a good amount of exercise and if your doctor is very happy with your lab values and other test results, then I am not sure there is any urgency to change your weight.”
You know how you feel. And you know if you're getting exercise. And your doctor can tell you about your test results.

Taking all that into account, it shouldn't be too difficult to decide if you actually need to lose weight. Maybe you want to lose weight because of some of the other benefits. Or maybe you're getting exercise, and everything else looks good, but gosh darn it you can't lose those pounds! If you can avoid fooling yourself about your BMI, your cholesterol, your level of activity, etc, you might find that you're either OK where you are or your goal of a healthy weight is more attainable than you thought.
Posted by James at November 21, 2007 11:18 AM
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I would like to see a detailed analysis of the diseases that people who are in the "overweight" BMI range are protected from. For example, if it were breast cancer (I don't think it is, I think fat cells, which release estrogen, increase your chances of developing breast cancer), then being overweight probably wouldn't help people who had no family history or genetic predisposition toward breast cancer... although maybe even that is a simplification. I think one researcher pointed out in that article that there's longer life and then there's quality of life.

But then again, they're talking about "overweight." Once you dip into "obese," then the death rate increases over the people in the "healthy" range or of the "normal" weight -- however you want to look at it.

I also wonder if changing your habits is a good thing. I think if your habits are generally healthy, your tests are good, etc., then you shouldn't suddenly start eating more to increase your life span, because I don't think anybody's shown a causal relationship. Genes don't exist in a vacuum, and in fact there isn't usually one "gene" for a trait. Other genes are part of a gene's environment, and they build a body together. It's possible that a combination of genes makes people overweight and also affords them protection against certain diseases. Or makes them want to eat more or certain foods and affords them protection against certain diseases... maybe a naturally "healthy" weight person who gained weight wouldn't have that same protection because it doesn't actually come from the weight, but from some other gene in the combination.

I think the only thing this study really tells us is that if you're overweight, exercising, and your numbers are good, that you shouldn't try to lose weight just to lose weight because it actually might not be good for you. But also take care not to eat more calories than you need to maintain your weight, or you could eventually become obese, and that isn't healthy.

Posted by: Maggie at November 21, 2007 11:35 AM

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