The Telegraph
Since 1st March, 1999
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Fat' Look at chubby chums
- Obesity may spread through social networks: Study

New Delhi, July 26: If a friend or a family member gains weight, be careful.

When someone becomes obese, so might their friends, siblings and spouse, says new research by US scientists.

The study, published today in the New England Journal of Medicine, shows that obesity may spread through “social networks” and cites this as one of the factors fuelling the obesity epidemic.

The researchers from the Harvard Medical School and the University of California, San Diego, have found that when an individual becomes obese, the chances that a friend will follow suit increase by 57 per cent. A sibling of an obese person has a 40 per cent increased risk while the figure for a spouse is 37 per cent.

“One person’s obesity can influence numerous others to whom he or she is connected both directly and indirectly,” said Nicholas Christakis, professor at Harvard’s department of healthcare policy and lead author of the study.

The effect, however, isn’t uniform across the sexes. It’s more likely to spread between male friends than between female friends, and seems not to spread to a sibling of the opposite sex.

A man’s chances of becoming obese rise by 100 per cent if a male friend becomes obese. But the female-to-female spread is not significant, the researchers said.

What exactly causes this social spread of obesity is unclear. Nutritionists and psychiatrists believe the findings merely reflect how friendship and socialisation can lead to adoption of common lifestyles.

“Friendship fulfils a certain need in individuals. And the friends we seek are likely to have some similarities -- perhaps in lifestyle choices, or in eating habits,” said Anjali Chhabria, a consultant psychiatrist at MindTemple, a clinic in Mumbai.

“Friends can influence each other on whether or not to exercise. If a friend does something, it’s okay to do it too -- like partners in crime,” she said.

“It’s not surprising. People who socialise tend to follow each other, shop together, eat together,” said Rekha Sharma, senior vice-president at the VLCC health clinic in New Delhi. “But there may also be changes in the way close groups view obesity.”

The US researchers believe the observed effects may stem from a change in perceptions within close social networks about what constitutes acceptable body size.

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

The researchers made the discovery by tracking obesity patterns in more than 12,000 people over nearly three decades in the US, where two out of three adults are overweight.

Christakis and his co-author John Gowler have suggested that this social spread of obesity may be exploited to actually combat the epidemic.

“Network phenomena might be exploited to spread positive health behaviour,” the study says.

A person may change his perception of risk of disease -- and possibly even lifestyle and behaviour -- depending on how friends perceive the risk.

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