Your friends are why you?re fat. The Eatery, an app from health technology startup Massive Health that lets users take pictures of their food and then asks them to rate photos of other users? food based on perceived healthiness, has yielded lots of data since it was launched last year. The key factor? Your friends. If they?re obese, you?re 57% more likely to be obese. The lesson: Watch what you eat, but watch what your friends eat, too. This works both ways, though. Pick healthy friends and you?re bound to get more healthy. A study found that while women with unhealthy friends also start to make bad food choices, women with healthy friends eat better.