what does the body use protein for
Proteins are the cell's 'workers'. You have many thousands of different proteins in your body. Some are used as building blocks: your hair and nails contain the protein keratin, while your muscles contain actin and myosin. Other kinds of proteins carry oxygen around your body, fight infections and detect the light entering your eyes.
Fuel for Exercise. Your body typically uses protein for fuel as a last resort. During exercise, as during rest, a combination of fat and carbohydrates generally provide the necessary fuel. The intensity and duration of your exercise sessions affect the percentage of energy used from carbohydrates and fat.