I drink a can of Pepsi Max everyday and if I don't have it, I get a headache in the early afternoon. There's half the caffeine in that can than one cup of coffee, but it stills have an effect on me.
I remember reading that diet soft drinks stimulate your apetite, so you're likely to eat more when you drink diet soft drinks.
Also, the ingredients in diet soft drinks are said to be quite damaging to your health in the long term, especially to your memory - aspartame and phenylalanine. It's been a while since I read about it, but I'm still drinking the stuff!
Just keep moving! And don't be lazy...
SW: 74.3kg - 1/1/09
CW: 71.1kg - 3/5/09