Is Obesity Contagious?
You are more likely to become obese if you have a sibling, spouse, or friend who is obese, say researchers who tracked more than 12,000 people who participated in the Framingham Heart Study from 1971 to 2003.
Women are influenced by other women only if they are mutual friends, the researchers found. Men are influenced by other men whether or not the friendship is mutual — that is, even if only one of the two identifies the other as a friend. And friends of the opposite sex have no impact.
The likeliest explanation: People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads.
Don’t worry that you’ll “catch” obesity, but do be aware that a friend’s weight may influence your thinking and eating. Of course, you could always influence your friends to move more and eat less! 
