I think it is fine, i dirink diet coke all the time. What is important is to make sure you dont drink soda (or anything else) as a replacement to water. Have a diet soda with meals, or as a snack, but drink plenty of water as well. (I think that is why they say no sodas - because once people think sodas are ok (non fattening) they drink too many of them - and as we all know excess is very bad for the diet ;-) ))))