It’s the krebs cycle. If you look at how sugar is broken down by the cells to make atp, the actual energy your cells use, it takes C6H12O6 (sugar) and makes it into a few CO2 and H2O, getting energy (atp) from breaking it down into the components. That CO2 is then exhaled, which is I think what OP is referring to.
Note: it’s been a long time since I learned that in class so it is most likely somewhat incorrect
I think more studies are still warranted. I agreed with you before, based on that available data, but later they have found that the bmi of people who use artificial sweeteners is the same as people who don’t.
2 takeaways can be considered here. First, that just keeps their palate attuned to extra sweetness, which if they just took a break for a bit from all sweetened stuff, even fruit might taste amazing again. Second, it’s possible that it directly affects their microphone, perhaps feeding poorer quality microbes which would lead to all kinds of things, perhaps increasing hunger for foods those microbes like, perhaps affecting their mood, etc.
But those really amount to the same thing. If you can cut sugar, and not supplement with other added sugar, you might consume more fruits and get the associated fiber, which is probably a good thing.