protein is not a better source of energy, they are consumed as energy source only when they are required to synthesise glucose de novo. You avoid carbohydrates (glucose) in your diet to make the body behave as if it was starving so:

-No insulin --> no signal of abundance --> no storage of energy in lipid tissue
-Keep consuming protein as energy source, however they have less energy than carbohydrate because you'll spend some energy in turning them into glucose --> they get consumed faster.