Personally, as a writer I have great difficulty writing when I'm trying to concentrate. It's actually quite unbelievable how much diet soda I go through, yet I write best (quality & quantity) when I'm chowing down on granola bars and candy. I think I drank an entire like uber-big gulp of coke in an hour and got out 2000 words, yet in the same amount of time I'm usually lucky if I get 500 words when I'm drinking Coke Zero.