Protein builds, maintains and repairs tissue. It does not like to be used as fuel.
If you are inactive, you should consume 1.0 gram of protein per kg of body weight per day.
If you are active, your protein requirement will range from 1.2 grams to 1.7 grams per kg of body weight.
Athletes who compete in endurance sports should eat around 1.2 grams of protein per kg. Body builders should consume around 1.8 grams per kg.
Your weight in kg = Your weight in pounds : 2.2
If you eat properly, the maximum amount of energy from protein that your body will use is 5 %. If you don’t eat enough carbohydrates and your exercise is long in duration, or you are very active person, your body will use up to 10 % protein for energy. And you don’t want that.
If your intake of calories on daily basis is low, well below the energy you need for maintenance, your body will use even more protein. While this is more common between athletes, it can happen to very active people too.