How bad?  Reeeeally bad.  

How 'bout this: Diet soda is as bad for your teeth as a meth addiction!

A new study published in General Dentistry examined some pretty jaw-dropping case studies of men and women who consumed as much as two liters of diet soda per day for three to five years.

They found that a woman in her 30s who drank two liters of diet soda daily for three to five years experienced tooth rot and decay remarkably similar to that suffered by a 29-year-old methamphetamine addict and a 51-year-old habitual crack cocaine user.

And yes, she had to have all of her teeth removed and replaced with dentures.

Stick with water if you are trying to cut calories!