Fluke or Trend? Is Overweight the New Optimal?

Black is the new white.  50 is the new 30.  I'm sure you've bumped into these new re-definitions in the lay press.  But when did overweight become the new optimal?  Before answering that question, let's set the ground rules.  Medically speaking, we claim you're normal weight if your body mass index (BMI) is less than 25kg/m2.  Overweight is 25-30kg/m2.  And all manner of obesity is greater than 30kg/m2.

However, the calculation doesn't take into account age, gender, ethnicity, frame size, body composition or anything else besides weight & height.  And therein lies the rub since it's possible to be "skinny fat" or "over-muscled".  You know what I mean.  Picture the skinny person who has no muscle on his/her frame or the bodybuilder or athlete w/disproportionate amount muscle relative to anyone else their height.  However, for the most part, this definition of normal works as there are relatively fewer skinny fat or athletic people walking around compared to the generally accepted two-thirds of us who are overweight or obese.

So you can imagine my surprise when a systematic review of 97 studies involving close to 3 million participants was published last week in JAMA in which the authors concluded that being overweight BMI was associated w/statistically significant 6% lower risk of all-cause mortality compared to normal BMI.  As expected, overall obese BMI was associated w/higher all-cause mortality, especially w/BMI >35kg/m2.  But even mild obesity w/BMI 30-35kg/m2 was not associated w/any different mortality compared to normal BMI.  This had to be a fluke, right?

Wrong!  It turns out that I had in my flash drive a study published early online in August 2009 (and finally in print in February 2010) in Obesity Journal in which the authors concluded that both overweight & mild obesity were not linked to an increase in years-of-life-lost compared to normal weight. 

Well, this may be true but I'm still not totally convinced that being overweight or even mildly obese is better for you than being normal weight w/reasonable body composition.  In fact, an August 2009 study published in the International Journal of Obesity concluded that being overweight in middle age increased one's risk of dementia later on.

So does that mean I'm going to live longer but w/dementia if I don't normalize my weight now?  If that's a consequence of overweight being the new optimal, I'll pass.

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