Disclaimer: The products and information found on this site are usually not supposed to change skilled medical advice or remedy. They'll provide recommendation and train you tips on how to rely carbohydrates and how to regulate your insulin. The primary cause that marathoners carbo-load (or eat a number of carbohydrates) before the race is to store up glycogen. It boils all the way down to saved power: glycogen and fatty acids. For those runners you see limping across the finish line, you can assume their bodies have tapped into fatty acid reserves