You don't get cavity in your teeth of sweeteners, nor does your body absorb it and gives it energy (calories).
But, your body still believes it gets sugar so it tells the pancreas to produce more insulin into the blood to lower the blood sugar even though it doesn't need to. And what the insulin does is that it blocks out (temporary until the insulin level goes down again) the fat burning system. And it will also make you crave more sugar as a result, but sweeteners will not satisfy that craving because it never gives the blood any sugar.
There are studies (not sure where I read this) that shows that people that drink/eat things with sweeteners (for example diet coke, most sugarfree products (like gum) etc) are still gaining as much weight as the people that instead choose the sugar options like "real" coke.
So please don't drink 44 oz of diet soda and believe that it's healthier for you.
Personally, I think I will stop chewing gum every day. Maybe chewing gum can be more like a treat I can get on saturdays :D