The issue isn't so much glucose as fructose. Have a read of this presentation

https://onlinelibrary.wiley.com/doi/full/10.1111/joim.12993

From my readings in this area, glucose is an issue once you've been 'triggered' by fructose - and we can make our own under high serum sodium conditions. Uric acid's part of the cycle, as are glutamates.

Lead author on that paper I linked has done a good bit of research. From that, I'd guess that, for someone who's got this 'trigger' enabled, a week-long fast can knock them out of it, then normal the normal glucose endocrine loop can take over.