According to a study that was recently published in The New England Journal of Medicine, having a friend become obese increases a person’s chances of becoming obese by 57 percent. Surprisingly, a friend's weight gain has more impact than that of family members. How is this "contagion" effect possible? Dr. Nicholas Christakis, a physician and professor of medical sociology at Harvard Medical School and a principal investigator in the study, told The New York Times that one explanation is that friends affect each others’ perception of fatness. When a close friend becomes obese, obesity may not look so bad. The researchers say their findings can help explain why Americans have become fatter in recent years.