In a mature adult eating protein without exercising will not add to muscle mass. This has been proven. Now there are new concerns about protein.
A large observational study showed that a high intake of protein from meat including processed meat and poultry is associated with an increased risk of dying prematurely of cardiovascular disease. "In contrast a high intake of protein from grains, beans and vegetables was not associated with changes in mortality rates".
The bottom line is this. Eat a variety of foods.. The days when it was OK to eat only meat and potatoes have faded into history.