The Obesity Paradox Probably Isn’t Real – Overweight Associated with Higher Mortality

The Obesity Paradox Probably Isn’t Real – Overweight Associated with Higher Mortality


Back in 2013, this article appeared in the
Journal of the American Medical Association: This well-done meta-analysis looked at 97
studies that examined the link between body mass index and mortality, and found that,
relative to those with a normal BMI, those with BMIs in the 25-30 range had a lower all-cause
mortality. The weight of evidence, it seemed, confirmed
an “obesity paradox” whereby people with higher BMIs lived longer. Cue the lay press with articles like this
one from Time magazine, speculating on the benefits of body fat:
And this one from Prevention, identifying four situations where you’re better off if
you are overweight. But a persistent chorus of researchers asked
if maybe this finding was an artifact of poor measurement. Maybe people who are sick, even if they don’t
know it, lose weight, inflating the risk of mortality in the normal weight group. Well that theory got a king-sized helping
of facts from this study, published in the Annals of Internal Medicine:
Using data from three large cohort studies, comprising over 225,000 individuals, the researchers
demonstrated that, no there was no protective effect of being overweight. In fact, there was a small, but significant,
added risk for all-cause mortality. What did this study do that the 97 in that
meta-analysis didn’t? They looked at maximum weight achieved over
the past 16 years in addition to current weight. This helps to account for those people that
lost weight due to underlying, perhaps undiagnosed, diseases. And when they did that, they found this relationship
between BMI and mortality: In the dashed line, you see the hazard ratio
for mortality associated with the various BMI categories based on the single, most-recently-measured
BMI. Note the slightly reduced risk among those
in the overweight category compared to the normal weight category. But when maximum BMI was used, the paradox
disappears. Overweight individuals have slightly increased
risk compared to those in the normal range. To drive home the point, the authors looked
at change in weight, and the results are just what you’d expect. People who lose weight were at much higher
risk of death than those who did not, regardless of what their BMI was to start with. In fact, those who had a normal BMI at the
most recent weight check, but who had been overweight in the past had a 19% higher risk
of death than those who stayed overweight the whole time. This doesn’t mean that weight loss is bad
for you. It suggests that weight loss is a sign of
underlying disease. The healthiest people were those that had
a normal weight all the time. The take-home here is that a single measurement
of BMI at one timepoint may not be that useful. Trends in weight are much more important. And unintentional weight loss is a major danger
signal. After all, we all know how hard it is to lose
weight when you are really trying to. If your patient is losing weight without putting
effort into it, it’s time to look a bit deeper.

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