Ah, I should've written a more generic "takes the place of" instead of space. I meant to ask something along the lines of whether the artificial sweeteners of diet sugar might be confused for nutrition by the gut bacteria. Basically, I was picturing a situation where the gut bacteria might try to "eat" the artificial sweeteners, but then don't end up getting enough energy from it and can't do the things they need to do.

Like how xylitol can kill mouth bacteria because they eat it instead of other sugars but can't metabolise it.

Yes! That's pretty much the mechanism I was thinking of.