Long distance marching

Hey t-maggers got a question about long distance training and the effects its going to have on my body. I have been working hard for two years now, 175 very lean and ripped. I am presently training for the famous Nijmegen marches in the Netherlands coming in July. Is there a certain ratio carbs-protein-fat I should be paying strict attention too??? I dont want to lose my size and I am also keeping up with my intense workouts 5-6 times a week. If anyone has some secrets tips to keep me in top shape give me some advice please!!!