Extra weight is no defense against aging,
says a demographer who argues that the apparent benefits from being
overweight are a mirage.
Wouldn't it be great, considering how many of us are overweight, if carrying a few extra pounds meant we'd live longer?
recent analysis of nearly 100 published studies involving almost 3
million people found, surprisingly, that being a little overweight was
associated with a lower risk of death than having a normal weight or
The sweet spot, as it were, appears to be a body mass index ranging from 25 to less than 30. The findings were published in early January in JAMA, the Journal of the American Medical Association.
But is the finding real? An editorial in the same journal
pointed to problems with BMI as tool for assessing obesity. And it
suggested that artifacts in the data might be another factor behind the
The lowest death rates in most studies have been seen
for people with a BMI between 22 and 25, the editorial point out. The
authors suggested that the most important findings from the analysis
were that death rates were higher for the obese (BMI of 35 or more) and
people who were quite underweight (BMI less than 18.5).
As luck would have it, Ryan Masters,
a demographer at Columbia University's Mailman School of Public Health,
has been looking into some of the same data that have been cited in
support of the so-called obesity paradox.
"I sort of gingerly came into this field and was blown away by the
debate surrounding it," he tells Shots. Some of the theories advanced
to explain the paradox include a beneficial metabolic effect from modest
fat reserves for the elderly and cushioning in case of falls, he says.
Masters decided to look at the data, and he found problems in plain sight.
of the studies excluded people who lived in institutions, like nursing
homes, skewing the results toward healthier people. Frail people would
be less likely to participate in surveys and studies, too, he says.
also found a problem that he said reminded him of a report about
falling cats in Manhattan. Researchers found, paradoxically, that cats
falling from windows on the highest floors of apartment buildings were
more likely to survive than those who stumbled out of window on middle
floors, say the fifth or sixth floors.
The theory (as explained in an episode of Radiolab)
is that the cats falling from high floors reached terminal velocity and
had time to turn themselves and land feet first — something the cats
falling from middle floors wouldn't have time to do.
Masters says there's a better explanation. A so-called selection effect
that is biasing the data, he says. All the reports about the falling
cats came from local vets who treated them. The cats that fell from the
high floors were far more likely to die on impact and never be taken to a
vet, Masters says, but a few survived. Those that fell from middle
floors and were in bad shape had a chance at survival. The vets saw more
of these cats, but many more died.
In the surveys of elderly
people, the overweight and obese are outliers like the cats that
survived a fall from a high floor. "They're probably not representative
of what's normal," he says. "They're probably representative of the
"The population we're most interest in studying — the older aged obese population — is simply not there," he says.
analysis Masters and colleagues did challenges the paradox head-on.
"The risk of mortality from obesity compounds and grows stronger as you
age," he says.
Indeed, their paper, published online by the American Journal of Epidemiology this
month, calls for a rejection of the paradox and a clear-eyed assessment
of the hazards the obesity epidemic poses to our aging population.
results caution against framing the obesity epidemic as a 'moral panic'
in which the harm administered stems more from ill-advised hyperbole
than from the real-life consequences of obesity," Masters and his
colleagues write. "In light of our findings, we are, on the contrary,
much more concerned about inappropriate denial of the epidemic's
consequences for US mortality. Our results suggest that major public
health consequences will track with the epidemic and that efforts to
stem its growth are probably well worth the investment."