Some sugar substitutes are more dangerous than the real thing. Gut bacteria break down the slow digesting bound alcohols and yield 2C/ gm compared to sugar at 4C/gm, but there the bound alcohols are denser, so there is about 1.25 times as much in them, per same volume and they are less sweet, so we use more. So now instead of sugar, which is digested at about 12 grams/minute, you get to feed your bacteria slow digesting bound alcohols and produce carbon dioxide, hydrogen sulphide, methane, and other hydrogen compounds in the gut and digest at a slow rate.
If you have the bacteria to digest them, you get calories. If you have the wrong bacteria, they can produce a number of noxious substances, including some uglies,
essentially poisons. It is our choice to eat or not.