I am training for a marathon and every time I start to get into the higher mileage within a couple days I start to get sick. I know it is just the extra strain on my body that causes me to weaken. What are some diet or products to help refuel my body when I train hard? Should I have one week where I focus on mileage and another weak to help in strength training to help break it up?
Depends on your goals, age, gender, height/weight and numerous other factors. Usually for marathon recovery people need to shoot for quality over quantity.
Look for what gives you the best nutrients. Loads of water too.
After said marathon you can usually be a little bit more forgiving on cheat meals/ additional caloric intake.