The worst thing about Diet Sodas is that not only do a lot of them contain bad artificial sweeteners, but they spike your insulin, just like sugar does. This makes it impossible to burn fat while insulin is high, defeating the purpose of drinking a diet soda to begin with. They've been linked to causing people to consume more calories because your body expects those calories to be there via insulin response, but they're not, and you end up eating more.
Indulging in refined sugars every once in a while is a good thing, though
