Obesity is socially contagiousPeople at risk if friends are obese
Obesity is socially contagious, with people more likely to be obese if their family and friends are already overweight, a study has found.
The findings confirm those of past studies, but the latest research focussed on the way obesity may spread within groups of friends and within families.
"When you see that something like obesity spreads among close friends and family members, this raises important questions about how it's spreading, said Dr Daniel J. Hruschka, an anthropologist from Arizona State University, who led the study.
"Is it because we learn ideas about acceptable body size from our friends and family members, or that we hike together, watch TV together or go out to eat together?
"If we can figure out exactly why obesity spreads among friends and family members, that can tell us where to focus resources in curbing rates of obesity."
The researchers interviewed 101 women from Phoenix, Arizona, as well as 812 of their closest friends and family members.
When they compared the body mass index (BMI) of the women, their friends and family, they found that women were more likely to become obese if they were part of a social network where many were already obese.
They also investigated whether the women's perception of what was an acceptable body size and shape contributed to the spread of obesity within social networks.
"You might learn what is an acceptable body size from your friends and then change your diet and exercise to try to achieve that, said Dr Hruschka.
"Or, you might not agree with what your friends or family members think, but still feel pressure from them to achieve some ideal body size.
"Finally, you may form an idea of appropriate body size by simply observing your friends' bodies, which in turn changes your eating and exercise habits."
The research team found only limited evidence for any of these, suggesting that other factors such as eating and exercising together may be more important in causing friends to gain and lose weight together.
In fact, when asked, many of the women said they would rather have one of 12 socially stigmatised conditions such as alcoholism or catching herpes, instead of being obese.
A quarter of the women surveyed sad they would prefer severe depression to obesity, and one in six told the researchers they would rather be blind.
"This study is important because it shows that while the clustering of people with larger or smaller bodies is real, it is not shared values between friends that accounts for it," said study co-author Dr Alexandra Brewis, director of the Centre for Global Health at the university.
"This gives us important clues about the best ways to tackle obesity as a public health issue; we need to focus on what people do together, rather than what people think," she said.
The findings are published online in the American Journal of Public Health.
This article was published on Mon 9 May 2011
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