Oddbean new post about login | logout I'll defer to you, as I don't really know, but if one were only eating fat and protein, so taking in almost no carbs to be broken down into sugar, wouldn't you be skipping the sugar step?
Protein is still being broken down into sugar, but it takes much longer than carbohydrates, so you feel fuller longer and it is not as taxing on the body. That’s why you cannot overeat on a protein diet.