I've participated in sports basically my whole life so dieting is something heavily ingrained in me. Transferring these from sports to meditation was a non-issue as I exercise most days of the week – I simply treated them as the same thing. Therefore I generally make sure to eat a meal with not much saturated fat or complex carbohydrates a few hours before. Naturally if spontaneity takes over I don't particularly worry though.
What is an issue are things like sugars and coffee; it's naturally hard to relax if these are pumping through the system. Coffee especially is a vice of mine. My job can be enjoyable (research and analysis), but often it can be painfully boring: tedious data entry or literally sitting doing nothing. A lot of the time I just resort to coffee breaks, although I've realised that since the proliferation of tablets, everyone can mistake seeing me sitting and reading a Kindle as me doing work so this might remedy the problem

Outside my personal experience, I have no idea what effect nicotine addiction has on people but I assume it's somewhat similar to caffeine?
I've also never fasted, which I view as a major personal shortcoming as I'm aware people use fasting as a beneficial practice both physically and mentally. I'd be interested if anyone has personal experiences/tips in this area.