The dentist told me that if i eat sugary foods, i would get brown marks. I did eat sugary foods, but i did cut back. I rarely had fizzy drinks, i don't have them too often anyway. I had like a chocolate bar or two a day and i didn't get any brown marks but when i could, i cleaned my teeth afterwards. If you clean your teeth after eating say a chocolate bar it should be ok, it was for me. I wouldn't eat chewing gum because it gets caught in the wires, just avoid that stuff. I think if you have fizzy drinks quite often, say 3-4 times a week it will stain your teeth. It really wouldn't be worth it having them for about 2 years and your life is ruined because of it.