Hi. My workouts are going well, but you know I'm always looking for ways to improve. I need to know if proteins are a fuel source for me. Because if they are I want to work on increasing my intake of them. So...? Considering Mario's workout, are proteins a fuel source for him? If you need to review Mario's registration form here it is. A. Yes, proteins are a source of energy for Mario's exercise along with carbohydrates. B. No, carbohydrates are the primary fuel source for Mario's exercise. Proteins are not a source.