Humans can become “sugar burners”, even at the mitochondrial level. Cells show a clear preference for burning glucose. The pathways for for the uptake and reregulation for burning fatty acids become atrophied with disuse.
This is probably why intermittent fasting, and calorie restriction, low-carb works so effectively. Critics say “starving yourself” but it isn’t starving, it forces the body to relearn how to do something it is intended to do - burn fat for energy. There is only one organ in the human body that requires glucose, the brain, and our bodies can synthesize all that is required from fat. Imagine that.
Well, I did. I've been doing 16hrs+ of intermittent fasting now for nearly four years with little improvement in fasting glucose numbers hanging just above 100.