I just ran 15 consecutive races in the last 15 weeks. The majority were halves, and last week ran a full, without adding distance. Although, this was my 3rd marathon in my lifetime (I prefer half marathons, enjoy them much better, but...) I realize that if you are consistent with training during the week, abs & 1 or 2 sprint work outs, with long distance on the weekend (or once a week), you can make your marathon within a good time. Take it slow the first half, don't feel like you have to make the 1:52 for the first half, just take it slow and reserve your energy for the last half. Believe me, you "will" have the energy the second half (and then some) if you pace yourself correctly. The key is not to go out too fast!!!! You'll lose it otherwise.
As far as diet, eat hearty and good foods, fruits, veggy's, milk (I prefer low-fat chocolate milk), it really helps!!! Then a few days before the race, each more of it, pasta, pasta pasta w/ veggy's that give you anti-oxidants!!!!
Another thing I've learned is that every person is different, so develop a training program that works best for you, and a diet that is comfortable for your body!!
Cheers! And happy running!