1) Before a marathon my advice is to stick to a big piece of steak and chips. The steak is full of protein and the chips are ideal for a high-carbohydrate intake. For those people who suggest that you are overloading your stomach know nothing about training, I have been running for over 20 years and have completed endless marathons all over the world. I have steak with chips about three times a week and find it to be more beneficial for my body than the frequently recommended bowl of pasta and vegetables.
2) Secondly, people suggest that when you're a runner you must not see it as a go ahead to eat fatty foods, or eating unlimited chocolates. Well, I'm having a intake of about 2 chocolate bars a day and I'm as skinny as a rake! Excessive fatty foods get burnt off whilst running, so I say choc away! Chocolate also provides a quick sugar intake to help your body sustain the energy it needs to still be awake at work and then conquer a long run afterwards.
3) Don't stuff yourself before a big marathon, it won't help. But it is important that you don't change your diet beforehand. It's not going to help! It's important that you have incorporate high energy fatty foods in your diet including steak and chips before a marathon.
4) I don't believe in powerade's! Drink plenty of caffeine fluids! At times I sit in the office and after a powerade or two I still feel tired, but I have one very strong coffee with no milk and I'm ready to be back on my feet for hours! Coffee is the key, don't let the media fool you. Have a cup of very strong coffee with no milk before the race; it truly gives you energy you need to sustain yourself and keep going for longer. It is also much cheaper than any other supposedly good energy drinks!
5) Run barefoot. Stay away from running shoes If you look back at history you would find some of the best African runners compete barefoot. Some of those records have still not been broken. South African Zola Budd did famously well for training and racing barefoot and it will work for you too.
6) Lastly, it's important to have the right sports wear. Heavy clothes are not the way forward.