Thursday, January 3, 2013

Being Overweight Is Not a Mortality Risk

In 2009 a study from Canada reported that slightly overweight people actually were at less risk of dying than people of normal weight (see this blog, July 9, 2009). That study generated a lot of controversy, understandably. One criticism was that the study included “only” 11,000 people, all of whom were Canadians; perhaps the results would not be not be generalizable to other populations.

Now a subsequent much larger study proves the Canadian study right. The most recent study is a meta-analysis of 97 separate studies of weight versus mortality that includes over 2.9 million people. The results show quite convincingly that people who were “overweight” by current government definitions (a Body Mass Index of 25-29.9) were 6 percent less likely to die over a given time period than persons of “normal” weight (BMI 18.5-24.9).

No one is suggesting that people should gain weight just to live longer. For one thing, mortality risk goes up dramatically for persons who are severely or morbidly obese. But the data do call into question the proper definition of “normal” or ideal weight. Perhaps the definitions of normal weight, overweight, and obesity need to be shifted ever-so-slightly to the right, towards slightly higher BMIs.

We may never have a true definition of “ideal” weight, because any such definition would probably have to take into account a whole host of other factors such as physical health and even happiness. But the current data does give one food for thought when it comes to understanding the meaning and value of government definitions of ideal weights.

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