Ideal diet for athlete, biology homework help

Scenario: You are coaching a client that is running their first half marathon. They weigh 65 kg and would be considered highly active (run 5-7 times/week) 
Question: 
•  Assume that this client’s significant other is also training, but instead of training for a half marathon they are training to complete the 5k that is held at the same time as the half marathon. Describe how this person’s diet differ from someone completing a half marathon.  Defend your answer using physiology and biology of Carbohydrate usage.