Why do I feel so much more inergized when my diet contains a high amount of protein? I've always heard that carbs are good for energy but feel much more productive after eating meat than anything else.

I only noticed this because most of the time, I can only afford potatoes, pasta, etcetera. As a plasma donor, I needed more protein, commited to buying and eating much more meat and I feel more alert and ready to take on anything than usual. What exactly causes this? Does protein get things moving or what?