Dr.Nicholas A.Christakis,a physician and professor of medical sociology at Harvard Medical School and a principal investigator in the new study,said one explanation was that friends affected each others perception of fatness6.When a close friend becomes obese,obesity may not look so bad.
You change your idea of what is an acceptable body type by looking at the people around you,Dr.Christakis said.
The investigators say their findings can help explain why Americans have become fatter in recent yearseach person who became obese was likely to drag along some friends. 7
Their analysis was unique,Dr.Christakis said,because it moved beyond a simple analysis of one person and his or her social contacts and instead examined an entire social network at once,looking at how a persons friends friends,or a spouses siblings friends,could have an influence on a persons weight.
The effects,he said,highlight the importance of a spreading process,a kind of social contagion8,that spreads through the network.
Of course,the investigators say,social networks are not the only factors that affect body weight.There is a strong genetic component at work,too.
Science has shown that individuals have genetically determined ranges of weights,spanning perhaps 30 or so pounds for each person.But that leaves a large role for the environment in determining whether a persons weight is near the top of his or her range or near the bottom.As people have gotten fatter,it appears that many are edging toward9 the top of their ranges.The question has been why.
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