I gave it up refined sugar for Lent this year and the difference was amazing. My problem is that when I have it at all, I crave it. (it really is a similar compulsion to alcoholism). I'm trying to limit it right now, but if I don't give it up altogether, I have little success.
The difference is amazing. I don't feel so tired at the end of the day. The only problem is that now that it's hot, I want ice cream!