Your best friend can make you fat - researchers

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - Could your best friend make you fat?

Researchers who have studied "networks" of obesity think so: they found that if someone's friend becomes obese, that person's chances of becoming obese increase by more than half.

Siblings and spouses also have an influence, although a reduced one -- people whose siblings became obese were themselves 40 percent more likely to grow obese, while people whose spouses became obese were 37 percent more likely to.

"This is the first (study) to show how obesity spreads through the social network from person to person to person," James Fowler of the University of California, San Diego, who worked on the study, told a telephone briefing.

Writing in the New England Journal of Medicine, the researchers said their findings show that obesity is contagious -- not like a virus is contagious, but in a social sense.

It may help explain why obesity is worsening exponentially across the United States, with two-thirds of Americans overweight and almost a third technically obese.

"It has become very popular to speak of the obesity epidemic. We began to wonder if it is truly an epidemic," Dr. Nicholas Christakis, a professor of medical sociology at Harvard Medical School in Boston, told the briefing.

Christakis and Fowler studied the records of 12,067 people taking part in the Framingham health study, which included most of the residents of the mostly white, middle-class town of Framingham, Massachusetts.