I actually prefer to run fasted/skip consuming anything during my long runs, it makes the logistics easier, it’s cheaper (damn gels get expensive), and you don’t run the risk of having a reaction, gastro or otherwise, during the race or afterwards.
I was a sugar burner for my first marathon, I carried gels with me but they were handing them out during the race, I didn’t think about it but the brand they were passing out was different from what I trained on (rookie mistake, NOTHING NEW ON RACE DAY!) so, being that I’m very cheap, I consumed the gels they were slinging instead of what I had in my belt, BIG MISTAKE! Gastro distress for the rest of the day, between them being “new” to my system and consuming so many (4:25 run time).
Just another reason keto rules when it comes to endurance.