if you are training for the marathon you will be putting in A LOT of mileage a week. when i ran 5K's and half's i would run 40+ miles a week. this burned a ton of calories and kept me super lean
but to answer your question as a runner you need to stick with fruits, veggies, and very lean meats like fish or chicken breast. carbs are very important.. the best carbs i used to eat were rice and sweet potato. obviously before your run i highly recommend those complex carbs 2 hours prior.. looking back i feel as though sweet potatoes were a mistake simply because root veggies are tough to digest. so for my advice is rice and a non acidy type of fruit that will help hydrate you but NOT close to your training or you will just throw it up