Interesting! Particularly that some hibernating animals feed their microbiomes.

As far as not becoming diabetic, it could be as simple as not eating for a period after the fat is accumulated. Many animals react to fructose by shifting metabolism from mitochondria to glycolysis (mediated by vasopressin and uric acid), triggering fat storage. But they all do this in preparation for food scarcity (hibernation, migration) - so their metabolism primarily shifts to ketones while there is no food.

This is a very neat survival trick as fructose (in fruit) typically spikes at the end of the summer, when food becomes scarce. The metabolic shift lowers O2 consumption, making low O2 environments survivable (e.g. naked mole rats), and it triggers the production or metabolic water, needed when there is no drinkable water (e.g. marine mammals)

Humans have this fructose reaction in spades, likely due to uricase mutations that happened over a couple of extinction events. Nicely presented here:

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

Interestingly (to me, at least) is that this reaction can be blocked with allopurinol, a gout drug. (Gout comes from excess intracellular uric acid.)

Also, we can produce fructose on our own; it just takes a surge of sodium.