Sport questions about nutrition

Sport Fitness
hi everyone. i am new and i have three questions.
1. i would like to know the importance of carbohdrates, fats, protein and water to an athlete.
2. also, what nutritional guidelines could be used in preparation for a marathon/triathlon.
3. what meals should an athlete have before and after a marathon/triathlon and why?

thanks in advance. if someone answers my three questions i would greatly appreciate it.
 
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