A crappy fairytale:
Once upon a time, someone noticed a decrease in Physical Education classes that happened around the same time as an increase in “childhood obesity”. Rather than apply that evil villain, Scientific Method, to the problem, they immediately began funneling money into schools to get more physical education to fight the omigod deathfat. Reasonable people, who were not alarmists from the United States, did a study (using the evil villain, Scientific Method). Turns out that the guess was not proved out and they may have nothing to do with each other. You can read the facts here: http://budurl.com/gymduh
The moral of the story? Despite the media and politician’s best efforts, your eighth grade biology teacher was right that CORRELATION DOES NOT IMPLY CAUSATION. Never ever, never ever, never ever. Not even when we’re talking about OMIGODDeathFat. Even then, Scientific Method prevails. Look, over there, is that a big flaming sack of duh?
Dances With Fat 
Big flaming sack of duh is the most awesome metaphor.