Professor Kylie Ball of Deakin’s Institute for Physical Activity and Nutrition looked at data from more than 3500 women across Victoria. According to the findings that those “who knew, or saw lots of other women exercising, or eating healthily, tended to be more physically active and eat well themselves, compared with women who didn’t see lots of others engaging in these behaviours.” That includes loved ones, best friends and family members.
Professor Ball attributed this to two key behavioral theories. Firstly, that we naturally gravitate towards those who share similar values or behaviours to our own. And secondly, that working out and eating healthy is essentially contagious - when you witness those around you adopting healthy habits, you take these to be the norm.
This isn't the first time obesity has been found to be contagious. If a good friend becomes obese, That increased one's chances of becoming obese by 57 percent. Dr. Nicholas Christakis, a physician, and professor of medical sociology at Harvard Medical School and a principal investigator in the New England Journal of Medicine's study had this to say: "You change your idea of what is an acceptable body type by looking at the people around you."
In other words, friends affect each others' perception of fatness. When a close friend becomes obese, obesity may not look so bad.