We're talking of the same thing from such different point of views it feels like we're debating here. You speak of human digestion from factual medical standpoint and I speak of optimazing energy levels for working out.

It's true that fats and protein are sources of energy, but the process of protein and fats breaking down is so long you can't get this fast and easy energy needed for heavy lifting with them. Also sufficient amount of calories, healthy diet nutrient-wise and not feel like throwing up from practical point of view without carbs is pretty hard. I'm also considering what type of diet is easy to follow here because bulking and lifting requires so so much calories