Sugar is not my friend (neither is caffeine).
I'm not going to get on some high horse and tell everyone they should give up sugar, I'm just going to tell you my experience. Sugar makes me feel bad. About five years ago I had a series of infections for almost four months. The doctor would treat me for one, and I'd get another. Another treatment, back to the first infection, first treatment, back to the second infection. Round and round.. After three months of that I got frustrated and started to look for other treatments - there HAD to be something out there that would help me feel better without just giving me yet another infection. The answer - quitting sugar. I went cold turkey and after about 10 days, no more infections! Hooray! I remained sugar free for about 5 months, and then started allowing it back in (it was the chocolate chips. I MISSED them).
Now I still don't eat very much sugar, and have been able to remain free of infections for the last five years. I can feel it when I eat too much. My body doesn't like it, and it's pretty clear when I've crossed a line. As for caffeine? Well, that just makes me jittery and it's not fun, so why drink it?
What about you? Are you a sugar-fiend? Or a paleo-person? Or halfway in between?