Proteins come in meats, fish, poultry, eggs, beans, nuts, dairy products and other foods (Fuel Bars!), and should provide approximately 12-15% of daily calories. Proteins give your body power to build new tissues and fluids, among other functions.

It is a common misconception that athletes need extra protein or protein supplements to build muscles. A certain amount of protein is needed to help build muscles but a nutritious, balanced diet will supply all of the protein that muscles need. Protein is your body's last choice for fuel (fat takes second place). It's very difficult for your body to convert protein to useable fuel, and the caloric yield is very low. Unlike carbohydrates, excess protein cannot be stored in the body and will be burned for energy or stored as body fat. Also, too much protein forces your liver and kidneys to process nitrogen byproducts which increase your fluid needs and may cause calcium loss and hence bone weakening.