I think people have chewed stuff forever. Obviously, sugar isn't good and most artificial sweeteners are just as bad. See this post by Mark. Now there is stevia gum. Mark likes stevia. Might be the answer. I have not tried it. Trident Extra Care gum supposedly rebuilds teeth. I don't know whether it does.
Tea should be ok.
We don't worry about counting calories. Intermittent fasting (skipping meals) is great. It has helped me a lot. As a newbie, you don't want to get carried away with it but sometimes skipping should be fine. Eat when you are actually hungry.