It varies by the individual, and for those who are fat adapted and not suffering from hyperinsulinemia, it works with a higher amount of carbs. While I eat low carb, it took some time consistently eating that way before I was able to be comfortable in fat burning mode. Note that whenever I go higher with carbs (not often), I'm getting them from veggies and nuts usually. I continue to produce ketones unless I really ramp up the carbs.

Now, if I consumed a bear claw or coffee cake with my morning coffee, all bets are off. Like alcohol to an alcoholic. I learned at an early stage that I cannot do that.