What happens to unused protein?

The body does not store excess protein as protein; just like any calories beyond the body's daily requirements, extra gets used as energy or stored as fat or muscle glycogen. Eating eggs or chicken is not what causes increased muscle development. What stimulates growth is the high intensity exercising that challenges the body and then requires repair. Protein simply provides our bodies with the essential amino acids, or building blocks needed to build lean muscle. First dietary protein goes towards maintaining muscle tissue mass and a range of other body functions. But if more is eaten than is needed, it too is converted to fat and stored.