One of my sister's friends is a secretary in a doctor's office. She told me that I need to be sure and get plenty of proteins in my diet because they are a great fuel source for when I do my aerobics class. She works for a really good doctor, so do you think I should take her advice? How should you advise Beth? If you need to review Beth's registration form here it is. A. Yes, proteins are a source of energy for Beth's exercise along with fats and carbohydrates. B. No, fats and carbohydrates are the primary fuel sources for Beth's exercise. Proteins are not a significant source.