The 2004 documentary Super Size Me
set out with a goal of showing everyone how unhealthy it is to eat nothing but fast food every day for a month. The movie wasn't done in any particularly controlled way, but it still seemed to provide some convincing anecdotal evidence for the common sense knowledge that fast food is usually junk food. But the counterexample for fast food is Jared Fogle
who lost an incredible amount of weight eating only at Subway (and has gone on to become Subway's most famous spokesperson). Does it really matter what you eat? Of course it does, but exercise and watching how much you eat is important, too. Here are just a few other weird diets that are trying to prove some point (with varying success).
If you'd like to read more awesome and interesting stuff, check out this unrelated (but not entirely random!) Techdirt post