Does your diet affect your game?

No, but water does. I used to not drink anything during games as I hate leaving the table, rushing to the johns and then rushing back to miss hands. But during a bout of the flu a few months ago, I was drinking 2 litre bottles of water every couple of hours and (to keep myself occupied) was playing online. And I found that my game really improved, even when I was playing without the flu - I was more aware of the other players and how they had played previous hands.