After spending months training for a marathon, the last thing you want to do is let an ill-advised meal ruin your run.

You need to eat something that can give you enough energy to get to the finish line, but it also needs to be something that won't sit in your stomach like a brick.

"Fueling your body for a marathon is important, but not all nutrients are created equal," says Kim Lowry, dietitian at Houston Methodist and experienced marathon runner. "In addition, the timing of your meals matters, too."

If you're looking for the best way to fuel your body for a marathon, consider Lowry's advice for setting your body up for race-day success.

Wake up early and eat the right breakfast

I'm sure you've heard that breakfast is the most important meal of the day. It should come as no surprise that race day is no different.

"As you sleep, your brain uses about one-third of the carbohydrates you have stored away," explains Lowry. "Replenishing this supply before a race is important because carbs are your body's primary fuel source while running a marathon."

This means that your pre-race breakfast plan should focus on replenishing your energy stores by eating carbohydrates that are easy for your body to digest (known as simple carbs).

"You'll want to eat about 60 grams of simple carbs about 3 to 4 hours before the race," says Lowry. "And while carbs should be your main focus, adding a little protein to your breakfast can help prime your muscle for better repair and recovery after the race."

A pre-race breakfast that has simple carbs and some protein includes:

• A banana
• A bagel with about 1 to 2 tablespoons of peanut butter

"Just make sure you avoid high fiber and high fat foods the morning of the race," warns Lowry. "These take longer to digest and can cause bloating or gastrointestinal distress during your run."

Lowry also recommends getting in one last dose of carbs right before the race.

"About an hour before you start, have another 30 to 60 grams of simple carbs," says Lowry. "I recommend something that's very easily digestible, like an energy gel packet or energy chews."

Your meals the day before the race are important, too

A good pre-race breakfast is important, but so are the meals you have the day before. And, no surprise here, carbs are the star of the show yet again.

"You want to eat a lot of carbs the day before running a marathon," says Lowry. "And you want to get most of them during lunch."

Lowry says to eat a big lunch that's about 80% carbs the day before the race. She recommends having:

• Pasta with meat sauce
• A burrito bowl with a lot of rice, low-fiber veggies and lean protein

For dinner, Lowry recommends the same food options as above, but to cut the portion size in half.

"By carbo-loading at lunch, you're able to saturate your muscles with the energy they'll need the next day — but also give yourself plenty of time to digest everything so you don't feel bloated in the morning," explains Lowry. "Following that with a smaller dinner can help maintain adequate carb levels without making you feel full when you wake up."