Rule No. 1 of pre-marathon nutrition is: "Nothing new for race day." During your long training runs, you should have been practicing your carbo-loading and experimenting with different foods in the days leading up to your long runs. So, when it comes to your pre-marathon meals, don't try any new foods -- just stick with your favorite pre-long run foods that you're used to eating and have never given your stomach issues.
What types of foods are best? Pasta is a traditional favorite among marathon runners, but other carbohydrate-rich options include bread, cereal, bagels, potatoes, oatmeal, quinoa, rice, pizza (go easy on the cheese) and sweet potatoes. It's also important to get some protein the day before your marathon, so include a 3-4 oz. serving of fish, meat or tofu in your dinner. Avoid high-fiber or gas-forming foods like beans and any type of food that may upset your stomach or can interfere with sleep.
If you're traveling to a new location for your marathon, make sure you plan your meals in advance and be sure your favorite foods are available in the race city. Some runners prefer not to take any chances and pack their favorite foods to bring with them.
The day before your marathon, spread your calories out throughout the day, so that you're eating something every two to three hours. Eat three normal-sized meals and two to four snacks. About 65-70% of your calories come from carbohydrates, so try to add an extra serving of carbs to your meals and make sure your snacks are mostly carbs. Stick to healthy options and try to avoid very sugary junk foods.
Try to eat your pre-marathon dinner somewhere between 4 p.m. and 6 p.m., so you'll have plenty of time to digest before you go to bed. If you eat on the early side, you can also have a small snack a couple of hours later.
Be sure to finish your breakfast at least 90 minutes before the marathon start. Don't have a huge breakfast and stick with mostly carbs and some protein. Some examples of good pre-marathon breakfast foods (again, don't experiment with any new foods) include: a bagel with peanut butter; a banana and an energy bar; or a bowl of cold cereal with a cup of milk.
Also see: Nutrition and Hydration for Marathoners