You’re swallowing a bit of the gum + saliva is the first stage of digestion. Think abt it like licking a lollipop; you’re not actively eating anything, but you’re still getting the calories. With lollipops, you eat everything except the stick. With gum, there’s some stuff left, but less than you started out with. If you let a chewed gum-wad dry out and then weighed it, it would weigh less than the full stick of gum did 🙂↕️