Body Mass Index (BMI): When Is It Too High?

A few years ago, the CDC reported that, contrary to conventional wisdom, being overweight was ok, possibly even healthy, although they did agree that being obese wasn't good for you.  Obviously, this stirred up quite a bit of controversy.  First, you have to understand that, for statistical purposes, overweight & obesity are defined strictly by weight divided by height squared in the metric system so that the units for body mass index (BMI) come out as kg/m2.  Quite obviously, this simple calculation won't take into account those with more muscle and less fat, eg athletes, bodybuilders, etc.  However, think about how many muscular athletes & bodybuilders there are, at least compared to the US population.  So by and large, this calculation & definition using BMI works.

With that in mind, the authors of today's study did some fancy statistical analysis of 1.46 million baseline healthy Caucasian adults (why? because that's the data that they had to work with) avg 58yo with avg BMI 26.2 (overweight) and followed for 10yrs.  In the ladies, they noticed a J-curve with lowest all-cause mortality at BMI 22.5-24.9, increasing on either side as much as 2.5x for those with BMI 40-49.9 (morbidly obese).  Most important to note is the statistically significant 13% greater risk of death from any cause even in those with BMI 25-29.9 or overweight.  Morbidly obese men fared worse with risk almost 3x that of those with normal BMI.  The other point to notice is that being rail thin isn't healthy either.

It would appear that the CDC study was more likely a fluke since multiple studies have since demonstrated findings similar to today's publication.  For instance, one study published in August concluded that in those men with heart disease, BMI was similarly related to mortality with risk starting at 25kg/m2 and up.  Another study published that same month but analyzing over 424,000 participants, came to similar conclusion of increased cancer mortality for both overweight & obesity.  Back in March 2009, another study of over 890,000 participants avg 46yo followed for 13yrs demonstrated lowest mortality in normal BMI even after taking into account the usual suspects with mortality increasing at BMI >25kg/m2.

The moral of the post is this:  BMI is just like Goldilocks, who wanted everything just right, not too much, not too little.