Fat provides 9 calories per gram, more than twice as much energy as protein and carbohydrate. A form of carbohydrate which your body can't digest. Fiber helps your digestive tract work. A major component of all body tissue. Your body needs protein to grow and repair itself.
Protein is also a necessary component of hormones, enzymes and hemoglobin.
Your body can use protein for energy, but that is one of its least important functions.