Environmental causes 

How can choosing to take less exercise and choosing to eat fast food be considered an "environmental cause"?  Only if people are not responsible for their own actions.  That obesity is a disease according to some in the rich West is so that drugs can be prescribed!  (You cannot get a drug approved unless it is for a "disease".)  Thirty years ago it wasn't a disease!  What's changed?  Personal behaviour.  As the article says:  We eat more, we eat more rubbish, we exercise less.  Doubtless there are environmental causes BUT what are they?