NEW YORK (Reuters Health) -
Obesity may be contagious
because most people feel good about themselves if they are
about as heavy as the people around them, according to new
research from an international team of economists.

This could explain the rapid rise in the prevalence of
overweight around the world, the researchers say. That is, the
norm that most people compare themselves to has become fatter
and fatter, feeding a cycle of “imitative obesity.”

“What we're finding is that human beings are probably
driven tremendously by comparison. Unless you understand those
comparisons, you're not going to understand the rate of
obesity,” Dr. Andrew J. Oswald of the University of Warwick in
the UK told Reuters Health. “Understanding the sociology of
obesity is much more important than understanding the biology.”

Last year, Oswald and his team note, Drs. Nicholas
Christakis of Harvard and James Fowler of the University of
California, San Diego published a study showing that people
were more likely to become obese if their friends and family
members were heavy.

In the current analysis, which they presented at the
National Bureau of Economic Research conference July 25 in
Cambridge, Massachusetts, Oswald and his colleagues attempt to
use an economic model to show why this happens. They analyzed
data from several sources on body mass index (BMI) and people's
perception of their weight for 29 European countries.

More than one-third of Europeans think they are too fat,
the researchers found, and people who are more educated were
more likely to think they are overweight.

The researchers also found that for women, satisfaction
with their weight depended on their own BMI in relation to the
average BMI for a woman of their own age living in the same
country. For their part, men who were overweight tended to be
happier if the people around them were overweight too.

The link between people's relative BMI and their general
life satisfaction is likely unconscious, according to Oswald.
“They may not be aware of it. Our computers can trace out these
patterns without the individual necessarily knowing them.”

So the average person doesn't mind being overweight if
people around him are too; hence he is “keeping up with the fat
Joneses,” Oswald explained.

However, for “high-status” individuals, being thin is
becoming more and more important, he added; this may explain
the rise of super-skinny models and actresses, as well as the
prevalence of anorexia among upper-middle class girls and boys.

It might be possible to change people's weight-related
norms by having them look at images and movies from decades ago
– when people were, on average, 20 pounds lighter, Oswald
suggested.

“They don't have to be 220 pounds,” he said. “Their parents
got on fine in their life at similar ages weighing many pounds
less.”