IMHO, just keep doing what you are doing, and let your body tell you what it needs. more calories, give it more calories. more fat, give it more fat. protein, give it that.
you can do this with low carbing.
drink plenty of water.
take some supplements.
Keep your water intake up!
i'm very impressed and envious! i am only up to doing 12k's right now, but am hopeful to do marathons. check out the exercise forum, trainerdan, fern, and nat are full of great advise.
oh yea, WELCOME
hope this helps
brenda