Excess weight won’t kill you? The rest of the story

photo: Spree2010 via Flickr

photo: Spree2010 via Flickr

The media always loves a sexy headline, and the recent study claiming that a few extra pounds won’t kill you is tailor made for headline writers.  Unfortunately, the substance of this study doesn’t live up to the hype.  Excess weight may not be related to excess deaths for reasons that have nothing to do with actual weight.

This wasn’t a study of actual people.  It was a study of studies with death rates compared to Body Mass Index, that arbitrary statistic that lumps people into weight categories: normal, overweight and obese.  According to this report, being a few pounds into the overweight category didn’t raise your risk of death.

That sounds nice, but there’s an enormous problem with this conclusion.  People who weigh less, and are officially normal weight may weigh less due to illness.  Cancer, anorexia, HIV/AIDS, dementia, old age, Type 1 diabetes, alcoholism, drug addiction, Crohn’s disease, ulcerative colitis, various other serious GI diseases and malabsorption syndromes can all cause weight loss, or at least prevent weight gain.  Technically those people are normal weight, but they’re also ill.  Comparing a generally healthy overweight 25 year old to a thin 25 year old with cancer or Type 1 diabetes or a serious drug problem, and concluding that the overweight person might live longer because of the excess weight is ludicrous.

Then there’s quality of life.  Let’s consider a 50-something overweight guy with Type 2 diabetes, hypertension, arthritis and high cholesterol.  This guy is alive thanks to numerous prescription drugs, tests, surgical interventions and possibly hospitalizations.  But he’s alive, and so he’s technically supporting the data that claims being overweight is no big deal.  But take away the medical care and he’s in big trouble.  Comparing overweight and obese people who are on chronic medical care to normal weight healthy people is also ludicrous.  Death is not the only measure of poor health we have.  In fact, given the ability of sophisticated medical care to maintain life well past its normal limits, death is a completely useless measure of the effect of excess weight.

Some medical experts think BMI is overrated as a meaningful measure of health and obesity.  I couldn’t agree more.  What we really need are cheap and convenient ways to measure percent body fat.  People can be normal weight, but high body fat.  And people can be in the overweight BMI range, but have very high muscle mass, as with some professional athletes.  The silly conclusions from this study serve to emphasize the fact that we need to ditch BMI as soon as convenient and accurate body composition measurement becomes available.  Then we can start comparing disease incidence to excess body fat, not just total weight.

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