According to some health professionals and what I've read online chewing gum too much could cause weight gain.
But I used to chew gum everyday as a teenager and never once did I gain any additional weight from chewing the gum.
However for some people chewing gun too often can make you crave more fattening foods so by chewing more gum may cause you to increase your consumption of more food.
Then by eating more food with more calories then you gain more weight.
But chewing gum alone should not cause any weight gain.
Some people say that by chewing gum it keeps them from wanting to eat more food so it may actually cause some people to lose weight.
But then again some people may want to eat more.
It just depends on the person.