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Tuesday 24th April 2018

Obesity 'contagious': study

30th July 2007

Close friendships can have an impact on obesity, a US-based study of social ties and weight trends has shown.


The research, published in the New England Journal of Medicine, studied the effect of social relationships on obesity patterns across the United States.

Researchers examined data collected from 12,067 densely interconnected people containing many families and groups of friends gathered from a major heart study spanning the years from 1971 to 2003.

They were surprised to find that obesity appeared to cluster in groups of friends, regardless of geographic distance, even more than in families.

The research team, from Harvard and the University of California, San Diego, mined contact details taken from participants' family members and one close friend during the heart survey.

Their analysis showed that when a study participant's friend became obese, the first participant's chance of becoming obese rose by 57%.

In friendship pairs where each identified the other as a close friend, the likelihood of 'catching' obesity from the other rose by 171%.

Study co-author James Fowler, a political scientist at UC San Diego, said social networks appeared to be far more important a factor in tackling obesity than simply diet and lifestyle.

He said the effect of friendship ties went deeper than the fact that people who have similar lifestyles are more likely to become friends.

For example, geographic location seemed to make little difference to linkages between clusters of obese and non-obese friends.

Friends who lived a 5-hour drive apart and saw each other infrequently were just as influenced by each other's weight gains as those who lived close enough to share weekly take-out meals or pick-up basketball games.

Instead, Fowler said, people were much more likely to pattern their own behavior on the actions of people they considered friends. But if the sentiment wasn't reciprocated, the named friend's bodyweight was unlikely to be influenced in return.

The figures for friendship compare with the influence a spouse's obesity has - an increased chance of 37% that the spouse will also become obese - and with sibling ties, which produced an increased risk factor of 40%.

In conclusion, Fowler said that having fat friends makes being fat seem more acceptable: "Your spouse may not be the person you look to when you're deciding what kind of body image is appropriate, how much to eat or how much to exercise." Nor do we necessarily compare ourselves to our siblings. "We get to choose our friends," he added. "We don't get to choose our families."


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