Overweight vs. Obese: Body Mass Index and Risk of Death
The media talk about "the epidemic of obesity" in terms one might associate more with a zombie apocalypse and the immediate destruction of civilization as we know it, so if you're a little tired of hearing about it, that's understandable. It's the media's job to grab your attention, after all.
But the truth is that being overweight or obese causes metabolic changes that lead to conditions such as high blood pressure or diabetes as well as an increased risk of death from heart attack, stroke, and other causes. Does it always? No. And there are those who are themselves overweight or obese who dismiss the risks because they have not developed these conditions.
Yes, it's true that one can be metabolically healthy and still be overweight or even obese. Doctors who counsel their overweight or obese patients on losing weight aren't being alarmist, however. The fact is that when it comes to weight, we doctors deal in percentages. If you read through just the research we've reported on here, you'll see "X% increased risk of [some condition]" here and "X% reduction in risk" there. Certainly there are those who roll the metaphorical dice and don't come up snake eyes (so to speak), but one of our roles as healthcare professionals is to help you minimize your risks of ill health or death, whether that's stemming from your weight or from intimate partner violence.
That's why the study we're reporting on today is so important. In the latest issue of JAMA a team of researchers from the National Center for Health Statistics, Centers for Disease Control and Prevention; the University of Ottawa; and the National Cancer Institute report on their review of the literature on Body Mass Index and the risk of "all-cause mortality," which includes any death from illness or natural causes but not, say, accidents or homicide (2013;309(1):71-82).
They identified 97 different prospective studies that reported on the relative risk of death asrelated to the World Health Organization's definitions of the categories of Body Mass Index (BMI). These are:
Body Mass Index | Clinical Definition of: |
Less than 18.5 | underweight |
18.5 to 24.9 | normal weight |
25 to 29.9 | overweight (preobese) |
30 to 34.9 | obese class I |
35 to 39.9 | obese class II |
40 and above | obese class III |
Calculate your own Body Mass Index |
The 97 studies included over 2.88 million adults - studies of children and adolescents were deliberately excluded, as were studies of those with specific conditions or about to undergo specific medical procedures.
Their results may surprise you. They found that when they limited their results to those individuals whose height and weight were measured by the original researchers (as opposed to being reported by the participant, which is prone to error), those with a BMI in the overweight range (25 to 29.9) were actually 8% LESS likely to die than those of normal weight (18.5 to 24.9). However, those whose BMI was over 30 (all three classes of obesity) were 11% MORE likely to die from all causes. A Body Mass Index of 35 or more had an increased risk of death of 32%. That's a one in three chance - or roughly your same statistical risk of rolling a one or two on a standard six-sided die.
What this means for you
We have known for some time that being overweight, by itself, does not put you at a higher risk of dying sooner. That said, when one looks at the research on those folks who ARE overweight and have developed associated complications like high blood pressure and diabetes, the risk of dying does go up. This research does confirm, however, that being obese comes with much higher risks.
There are those who will sieze upon these results and say, "See?! Even though I'm overweight, I don't need to worry about my weight because my risk of death is lower than those of normal weight!" While that is true, strictly speaking, "all-cause mortality" is not equivalent to healthy. It just means "not dead." The risk of chronic health conditions like diabetes, high blood pressure, and arthritis is still higher.
Quality of life is as important as how long you live, and it is clear that those of normal weight are much less likely to be burdened with disease.
First posted: January 2, 2013