The NY Post just ran an article, How Bradley Cooper put on 30 pounds for 'American Sniper.' My first reaction was, oh boy, another actor goes on steroids.
Sure enough, the article talked about how Cooper ingested 8000 calories a day for his role, and trained up to four hours a day with his personal trainer, and "didn't want to use any steroids or hormones or anything" -- the usual garbage actors spout after going on the juice.
I then Google-imaged "Bradley Cooper American Sniper" to confirm my suspicions and saw these pictures:
Cooper actually does look as if he remained clean (i.e., he doesn't look all that great). He looks as if he put on maybe 10 pounds of muscle and 20 pounds of fat. But at least it's a natural look.
This is the only instance I've ever heard of when an actor, or his rep, talked about how hard he worked to gain muscle naturally -- and he actually did it naturally.
I haven't seen the movie yet, but my son, who's generally a harsh critic, said it was excellent.