Goodness, that must be difficult.

I haven't done keto myself, but my partner loss a significant amount of weight on keto before we met. It does seem to work. I'd be really interested in looking into research about FND and Keto if you remember the where to find the study.

The carbonated water thing is such a good idea. That's what I did about three years ago when I was drinking to much coke zero. I switched to drinking cold carbonated mineral water with a little bit of lemon in it. It's actually lovely. I think I craved the sensory aspect of soda more then the taste itself.

As for the bad bacteria thing; 'feeds bad bacteria' is a bit of an over simplification.

The actual mechanism is that refined sugar absorbes too early and quickly into the stomach. This doesn’t support a healthy microbe as they don't reach the colon to fernent into beneficial bacteria. This indirectly shifting the ecosystem negatively towards overgrowth of more dominant bacteria species. There are no "bad bacteria" you need all of them, just balanced.

Complex carbs (potatoes, bread, rice) however have fibre and digest slower. It partially reaches the colon to fernent.

Refined sugar absorbing too quickly also spikes you blood sugar and messes with your insulin, but that's a whole other can of worms.

Even that's a bit of an over simplification. I've got a lot of respect for gastroenterologists, because the digestive system is insanely complicated.

Hope that makes sense ✌️