With increased mileage comes increased appetite. It takes calories to run and the secret is to add healthy calories to your diet. (You do need to add calories to your diet. This is no time to try to lose weight. You may lose weight, but eat when you are hungry.) Keep Power Bars in your car and briefcase so that you avoid fast food joints. Eat a baked potato with no fat sour cream as your late night snack. Buy bananas and fruit juice every time you grocery shop. Eat three meals a day.
Do I sound like your mother?
Think about what you eat the days preceding your long runs. Find foods that seem to work and agree with you. Ideally you should eat a familiar diet that works with your system the day before the marathon... Yes, you may have to bring your own food to an out of town marathon if your body is fussy. Only you will know this. You can risk some changes in your diet and habits now but during the two weeks before the marathon, I ask that you eat what is normal for you and not to try any strange diet or carbo-loading system. For instance don't try eating whale blubber in Alaska, or stuff like that. Many a marathon disaster is caused by trying things people tell you at the last minute.
Marathon week is no time to try new anything. That includes new foods, socks, shoes, stretches, or even sexual positions!