Is overweight
okay?
(This article was first printed in the November
2006 issue of the Harvard Health Letter.
For more information or to order, please go
to http://www.health.harvard.edu/health.)
The percentage of Americans who are obese has
more than doubled since the 1960s. In 1960, about
13% of Americans were obese, defined as having
a body-mass index (BMI) of 30 or more. (For most
people, a BMI of 30 means being about 30 pounds
overweight.)
Now over 30% of the population weighs enough
to be considered obese. Experts agree that this
is terrible news for the country’s health.
Obesity greatly increases the risk of diabetes,
gallbladder disease, heart disease, high blood
pressure, and several types of cancer (colon,
esophageal, kidney, and postmenopausal breast
cancer).
But what about being just a few pounds overweight?
Certainly the trend line isn’t as dramatic.
In 1960, about 31.5% of Americans could be classified
as being overweight, defined as a BMI of between
25 and 29.9. That percentage has crept up by
just a few points, to about 34%. Meanwhile, research
has caused some confusion about whether being
overweight (as opposed to obese) is really all
that bad for you.
In 2005, federal health researchers caused quite
a stir when they reported that their analysis
of data from national health surveys showed that
being overweight didn’t increase the risk
of dying prematurely. (They also found that the
mortality risk from obesity was lower than it
had been in previous years). Better treatments
for heart disease and conditions related to being
overweight was offered as an explanation. But
the study came under some sharp criticism for
(among other things) not taking into account
that the mortality rates in overweight people
might look good compared to those for thinner
people because some thinner people might have
been skinny because they were suffering from
underlying chronic illnesses.
A different group of federal health researchers
reported the results of another large study of
body weight and mortality in the Aug. 24, 2006, New
England Journal of Medicine. They made some
adjustments to deal with the confusing effects
of chronic illness. They also focused on people
who never smoked. Smokers tend to be thinner,
so if they’re included in a study of body
weight, they can make staying trim seem unhealthy
when it’s really smoking that’s responsible.
When these authors honed down their analysis
to people who didn’t have a chronic illness
and didn’t smoke, there was no free pass
for the few extra pounds. People who were overweight
in their early 50s were 20%–40% more likely
to be among those who died during the study’s
10 years of follow-up than those with lower BMIs
(23.5–24.9).
All this goes to show how difficult it can be
for researchers to sort out risk factors, particularly
one like body weight, which is both a cause and
an effect, and which is influenced by so many
factors.
It may also say something about the BMI. We
like our health information short and snappy,
boiled down to few simple numbers, and the BMI
fits the bill. But it’s really just a convenient
proxy for the real culprit, the metabolic effects
of fat tissue, particularly the most metabolically
active form that gathers in our bellies. Moreover,
people with the same BMI can be carting around
very different amounts of belly fat, depending
on how much muscle they have and how the fat
is distributed in their bodies. Several studies
have suggested that the good old-fashioned waistline
might be a better indication of how much unhealthy
fat we have — and should get rid of.
(This article was first printed in the November
2006 issue of the Harvard Health Letter.
For more information or to order, please go
to http://www.health.harvard.edu/health.)
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