Obviously we're adept at monitoring our intake, so the eating more because of the diet drink segment is irrelevant, but the possibility of metabolic manipulation is a different story. Note how she didn't focus merely on the weight gain issues but on various other negative health effects.
Can diet soda alter the metabolism by manipulating neurochemistry?
http://abcnews.go.com/Video/playerIndex?id=4271537
Resistance Starch...SEE THIS!
http://abcnews.go.com/Video/playerIndex?id=4273328
Study mentioned:
http://www.apa.org/journals/releases...8-swithers.pdf