Mountaingoat - The best advice I can give is listen to your body. If its a training run I only eat if I have too. That way you are training your body to use fuel more effciently. I read all the books while training for my first marathon and most of it is too generic. As I said before, 10 miles is my comfort limit without more fuel but I can run 15 before it really starts to impact on performance. When I think back back to my first marathon i'm almost embaressed to say I had a bum bag with gels and flapjack in. You live and learn. I ran a 100k race last year and I met a guy after who had run the whole 62 miles on a bag of crisps and a banana! to me that is insane but it worked for him.