If you thought that over-eating and a lack of exercise were solely responsible for that expanding waistline, think again. Get that fat facts right and learns that the usual suspects aren’t always the only ones at fault.

If a new research on obesity is anything to go by, you might want to start choosing your friends very carefully. In a curious case – one as curious as that of Benjamin Button, US findings show that obesity can be contagious!

Now we’ve all heard the usual advice dished out on how to avoid piling on the pounds: adopt healthy diets and sleeping habits and exercise adequately. And sure, who hasn’t heard of catching the flu bug or the highly contagious chicken pox or measles virus from someone else?

But obesity, you ask incredulously? You’re not the only one stumped. Obesity isn’t infectious – so just how does one fat person cause another to become fat? When a fat person sneezes, can he pass the fat virus to the person standing next to him?

The fat friend factor

It’s all a simple case of not what you know but who you know. And it holds true when it comes to your body weight. US research reveals that your friends can make you fat. As absurd as it sounds, a study coauthored by Nicholas Christakis of Harvard Medical School and James Fowler of UC San Diego suggests that obesity is socially contagious; spreading from person to person in a social network.

The study finds that if one person becomes obese, those closely connected to him have a greater chance of gaining weight or of becoming obese themselves. What immediately comes to mind, logically, would be family members.

Surprisingly, however, the greatest effect is seen not among people sharing the same genes or the same household, but among friends.

If a person you consider a friend becomes obese, the researchers found, your own chances of becoming obese go up 57%. Among mutual friends, the effect is even stronger, with chances increasing 171%. The sense of what constitutes normal body weight passes from one person to the next.

Christakis and Fowler also looked at the influence of siblings, spouses and neighbors. Among siblings, if one becomes obese, the likelihood for the other to become obese increases 40%; among spouses 37%. There was no effect among neighbors, unless they were also friends.

fat and phat in love…:P

The researchers analysed data over a period of 32 years for 12,067 adults, who underwent repeated medical assessments as part of the Framingham Heart Study. They mapped a densely interconnected social network of the study’s subjects by using tracking sheets that recorded not only the subjects’ family members, but also unrelated friends who could be expected to find them in a few years.

The network map took two years to assemble and includes information on the participants’ body mass index. Among the first things the researchers noticed was that, consistent with other studies finding an obesity epidemic in the US, the whole network grew heavier over time.

Also immediately apparent were distinct clusters of thin and heavy individuals. Statistical analysis revealed that this clustering could not be attributed solely to the selective formation of ties among people of comparable weights.

Further analysis also suggested that people’s influence on each other’s obesity status could not be put down just to similarities in lifestyle and environment – for example, people eating the same foods together or engaging in the same physical activities.

Not only do siblings and spouses have less influence than friends, but also geography doesn’t play a role. The striking impact of friends seems to be independent of whether or not the friends live in the same region.

Distance irrelevant

“When we looked at the effect of distance, we found that your friend who’s 500 miles away has just as much impact on your obesity as the one next door,” said Fowler, an associate professor of political science at UC San Diego and an expert in social networks.

In part, because the study also identifies a larger effect among people of the same sex, the researchers believe that people affect not only each other’s behaviors but also, more subtly, norms.

“What appears to be happening is that a person becoming obese most likely causes a change of norms about what counts as an appropriate body size. People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads,” said Christakis.

“This is about people’s ideas, their bodies and their health,” Fowler said. “Consciously or unconsciously, people look to others when they are deciding how much to eat, how much to exercise and how much weight is too much.”

The policy implications of the study, the researchers say, are profound. The social-network effects extend three degrees of separation – to your friends ‘friends’ friends – so any public health intervention aimed at reducing obesity should consider this in its cost-benefit analysis.

When we are helping one person to lose weight, we’re not just helping one person, but we’re helping many. And that needs to be taken into account by policy analysts and also by politicians who are trying to decide what the best measures are for making society healthier. It’s important to remember that not only obesity is contagious but thinness is contagious too.

And so, because the opposite also holds true: i.e. people whose friends lose weight over time are also more likely to become thinner themselves, researchers stress that this should not by any means make people ditch their heavier friends.

Experts stress that people with more friends tend to enjoy better emotional and cognitive wellbeing. Health-conscious friends improve their health and their friends’ health as well.

Instead, they say that the findings should encourage people who want to lose weight to motivate their circle of rotund friends to do the same.