Good point, but I'm guessing there are more people out there with the poor diets, drinking diet soda and not exercising. It would be interesting to see.
I have often heard and read that carbonated beverages like soda, regardless of diet or not, are not good for your body. Granted, one or two a month might not do any serious damage, but, I bet having one per day is not something that's beneficial.
My sister is addicted to Diet Coke and is always craving cookies and pizza. Having read this, it all makes sense.