Excess of any food is stored as fat if your total calories (combination of protein, fats & carbs) exceed your body's needs to maintain its weight. In other words, anytime your body receives more calories, from any food form, than it burns in any given time period (e.g. day, week, etc), the excess calories will be stored as body weight/fat. But if you consume more protein than the body needs to perform all protein’s primary functions (building/maintaining tissues), the excess protein will be converted to energy. That energy will stored as fat only if your total calories from all foods are in excess of your burn; otherwise it will be used as an energy source to help fuel the body just like carbohydrate.