Sugar has a HUGE effect on my skin. At a time in my life when I was eating tons of high-glycemic fruit like mangos and bananas and drinking a couple of smoothies a day, plus occassional candy, my face was absolutely out of control. I looked like a monster. I had to stop eating that way rather abruptly due to some blood sugar issues, and it was almost an overnight change in my skin. I started eating a TON of healthy protein like beans, eggs, and yogurt and limited my fruit to low-glycemic fruits only (berries mostly), and once a day or less. I also got very strict about whole grains only, and started working harder on balancing my grains and other carbohydrates with a protein.
Of course everyone's body is different, and yours might not respond to sugar exactly like mine does. But it is certainly worth a try.
Another thing that I think might have contributed to my sudden change is yogurt. Probiotics are said to help treat acne. It seems like my face is a bit clearer when I eat a cup or more of yogurt a day. You could also try probiotic tablets from a health food store if you aren't fond of yogurt.
