Looks like somebody already mentioned the study on this topic that I had heard about and was going to bring up. As for diet soda etc. and anything with fake sugar, I just don't think they're good for you regardless. Too many funky chemicals with unknown long-term effects (besides, they just taste icky IMHO). Try putting a little bit of honey in the green tea and see if you like it better that way. You can also add lemon juice.