Thanks for all the thoughts so far - fun to read!
In my little brain there was always this number 9 - 9 calories in a gramm of fat, 4 in a gramm of glucose. Then I thought hmm, using fat seems preferable which makes those who can do lots of stuff with fat more likely to survive (Darwin again) then the organism depending all on glucose. Now, if the body does the majority of storage in fat it is safe to assume that it will be originally optimized to use this fat. Until we make ourselves carb adapted and lose fat adaption. And again optimisation kicks in: if a process is not “needed” - burning fat - its resources will be reassigned to somewhere else. Things actually change. And if you go without food for a while your body will use glycogen stores assuming that there will be more carbs again in the near future. And it cant use fat anyways, so it needs that fuel.
Once you become fat adapted again there is no need for the body to tap into your glycogen stores all the time - it makes sense to use as much fat as possible for anything because of the hundreds of thousands of years we actually took to optimize these processes based on the 9 advantage.
Thats why I was pondering this responsiveness question. Because if things are as described it should not be a lack of glucose that delivers you to the tiger after all The genepool with that defect should have been eaten long time ago :)))
Anyways, I gain the picture that once you are fat adapted your body keeps the glycogen stores for absolute emergencies and recharges them continuously if the chance arrises. GNG does not need to be fast (it still might be though!) because it works with a buffer.
BTW, I am also tending towards that after a meal fat metabolism does not kick in suddenly only after insulin drops under a certain value of x - in a fat adapted body the transition to me seems continouus but not linear. If you do not run down your stores anymore you might go into using fat again only a few hours after a insulin kicking meal. Ketosis not yet, but using fat already. Does getting into ketosis speed up, too?