What you eat before a race is just as important as how hard and how long you trained. Your body needs fuel to make good time, and the best way to fill it up is with a carb-heavy meal. During the week before your race, set aside the diet advice, grab a couple packs of pasta and help your body prepare to run 42 kilometers.

Food and the wall
To understand why what you eat is so important to how you run, you need to know what happens when a runner hits the wall. Toward the end of a race, many runners start to feel like they can't take another step. This goes beyond your normal post-workout exhaustion - runners feel sluggish and fatigued, and their speed suddenly drops despite their best efforts. This makes athletes frustrated, and they begin to wonder if they can physically finish the race. Some even drop out, defeated. 

"Carbohydrates are the primary fuel your body needs to run a marathon."

There's a scientific explanation for this phenomenon, and it has to do with how your body stores and uses energy. Carbohydrates are the primary fuel your body needs to run a marathon. They're stored as glycogen in your liver and muscles, and your body processes them quickly and efficiently. This is what gives runners their power at the beginning of a race.

After a while, your body uses up all its stored glycogen and turns to fat for energy. Fat is a lot harder to metabolize, and the process produces ketones that make your muscles hurt and leave you feeling exhausted. Once this happens, a runner loses about 30 percent of his or her speed, according to the Harvard Gazette.

To avoid hitting the wall, many runners use a practice called carbo-loading. They increase their daily amount of carbohydrates about a week before the race, getting anywhere from 85 to 95 percent of their calories from carbs. This gives their body enough time to store ample amounts of glycogen for an endurance run.

Designing meals
Runners World suggested runners start increasing their carb intake five days before their race and really focus on carbo-loading during the last two days.  While you don't need a diet limited to rice and white bread, you should take care not to consume too much fiber, fat or protein. These fill you up more quickly than carbs, are harder to digest and can lead to stomach problems during the race. 

The best way to carbo-load is to include food with a large amount of carbohydrates at every meal. Try a breakfast heavy on peeled fruits and oatmeal, then eat cereal, trail mix, a banana or all three as a snack. Pasta is a good staple for lunch or dinner, as are rice-heavy dishes like burritos or a lightly spiced paella. Other food choices include pita bread, beans, potatoes, nuts, seeds and legumes.

With your months of training and a carb-heavy diet the week before, you're ready to ace your next marathon.