Researchers find weight gain transmits socially

Whether you are a size 4 or a 24 may depend on the friends you keep.


U.S. researchers have found evidence that obesity is socially contagious, that weight gain can spread from person to person through a social network, much like the domino effect.


The study, the first of its kind to look at how complex social environments affect obesity, revealed that a person’s risk of gaining weight increases by 57 per cent if one of their friends becomes obese.


And, the researchers reported, that cascade effect is seen in up to three degrees of separation, or to that person’s friend of a friend of a friend.


“We were surprised that people to whom you are directly connected have such a strong effect on your obesity outcome — and how far that effect seems to spread,” said study co-author James Fowler, an assistant professor of political science at the University of California at San Diego.

It seems that friends can have as strong or a stronger effect on obesity than genes, gender, or even socioeconomic status, he said, pointing out that the results were symmetrical, that thinness is also passed through a social network.

Published yesterday in the New England Journal of Medicine, the study is getting rave reviews from obesity researchers who say the findings highlight new ways of combating the obesity epidemic. The

Canadian Medical Association reports that 60 per cent of Canadians — close to 20 million — are overweight, including some 5 million who are obese and who are at higher risk of dying from type 2 diabetes, heart disease and stroke.

Diane Finegood, scientific director of the Institute of Nutrition, Metabolism and Diabetes at the Canadian Institutes of Health Research, called the study “extremely important” and said health professionals could soon use social networks to deliver more effective obesity intervention strategies, such as spreading a dose of daily physical activity and other healthy behaviours.

Surprisingly, the researchers found friends have more influence on body size than siblings and spouses, and that the cascade effect was more than just “like attracting like.”

“It’s not that birds of a feather flock together, that obese people hang out with obese people and normal-weight people hang out with normal-weight people,” said Nicholas Christakis, a physician and professor at Harvard Medical School and a study co-author. “We found evidence that one person’s weight gain causes another person’s weight gain, that they actually influence each other.”