I think everybody oversimplifies the issue. Are you overweight because your friends are overweight, are your friends overweight because you are overweight, or

I think everybody oversimplifies the issue. Are you overweight because your friends are overweight, are your friends overweight because you are overweight, or are all of you overweight because you live in the same unhealthy culture? Could be that there is no causation at all - just meagre correlation: your friends have nothing to do with your weight, maybe it's just because all of you live close to McDonald's, your close proximity allowed for stronger friendships and bigger bellies. My (German) hometown friends are all thin, maybe because there is no fast-food around, maybe because we have to walk more to get to places, maybe because of a different food-culture we all come from - in this case, it has nothing to do with what I do with them, but what the environment does with us as a group.