Build the Best Pre-Marathon Diet to Fuel You From Training to Race Day

The word "diet" calls to mind fast fixes and a focus on weight loss. But when you're training for a distance as demanding as the marathon, a restrictive approach can leave you too depleted to log all your miles.

Instead, focus on consuming enough of the right kinds of energy to fuel your performance, says Dina Griffin, a board certified sports dietitian and registered dietitian nutritionist at The Nutrition Mechanic. What works for one runner might not work for another, she stresses. Bodies respond differently to eating patterns based on factors like age, running experience and any underlying health or medical issues.

Still, there are some general guidelines to follow based on exercise science and the experience of athletes and nutrition pros over the years. Here, a starting point for your own pre-race fueling plan.

Read more: What to Eat When Training for a 5K

As you ramp up your mileage over the weeks and months before the race, you'll want to make sure you're getting enough calories and nutrients to withstand the stresses you're putting on your body.

Eating a variety of high-quality, whole foods — think lean meats, fatty fish, whole grains, dairy and a colorful array of fruits and vegetables — works well for most people, says Lydia Nader, RDN, founder of RUN Performance Nutrition in Chicago.

From there, you can consider your balance of the big three macronutrients: carbohydrates, protein and fat.

Though some athletes tinker with high-fat, low-carb diets, for most people, "carbs are still king when it comes to fueling your endurance sports," says Tom Holland, a certified sports nutritionist and author of Swim, Bike, Run, Eat.

The more miles you run, the more critical carbs become. Aim for about 5 grams of carbs per kilogram of body weight — that's 2.2 pounds — per day (so, a 150-pound runner would need about 340 grams), Nader recommends.

Protein enables your body to repair muscle tissue, grow stronger and stay injury-free, Nader says. She advises athletes to consume about 1.2 grams per 2.2 pounds of weight per day, while Griffin will target as high as 2 grams per 2.2 pounds per day. That's anywhere from about 82 to 136 grams of protein for a 150-pound runner.

And then there are fats. While she doesn't usually set a specific target, Nader encourages her athletes to eat plenty of healthy fats — including the anti-inflammatory omega-3 fatty acids found in fish like salmon, as well as walnuts and flaxseeds.

"When you train for a marathon, you are just putting your body through a lot of inflammation," Nader says. "There's a huge benefit to trying to alleviate as much inflammation from the inside out as possible."

Read more: What to Eat Before Running a Half-Marathon

In the last few weeks before your marathon, you'll probably notice fewer miles on your training schedule. This is called the taper. The point? To allow time for your body to absorb all the hard work you've put in, so you can line up on race day recovered, refreshed and ready to run your best.

Eating as much as you did when your mileage was higher could leave you feeling sluggish. But instead of thinking about cutting back, try shifting the balance of your meals, Griffin explains.

"I recommend focusing on quality proteins and fats, and filling your plate with more vegetables than grains," she says. "Then, there is still a good volume of foods that provide sticking power, but we aren't over-consuming carbohydrate calories that we may not need as much during taper time."

Nader advises her athletes to pile their plates high with colorful veggies and fruits — the more different hues you consume, the wider the array of immune-boosting vitamins and minerals you're getting. This supports your body's recovery and helps prevent you from getting sick in the last few days before the race, she says.

Read more: The Perfect Post-Marathon Recovery Plan to Bounce Back After a Big Race

For some long-distance runners, loading up on carbohydrates has an ergogenic or performance-enhancing effect. A study published in the August 2011 issue of the International Journal of Sports Medicine found London Marathon runners who'd boosted their carb consumption the day before the race ran faster and maintained their pace late in the race.

To do it right, you'll have to consume more than 7 to 10 grams of carbs per 2.2 pounds of body weight per day in the two to three days before the race. That means 476 to 680 grams of carbs for a 150-pound runner. (For reference, the average bagel has about 50 grams of carbs.)

Aim to get most of them from simple carbs like fruit, fruit juices and refined grains. Complex carbohydrates, like whole grains, are usually smart choices because they contain fiber and other beneficial nutrients. But this is one case where you want quick energy, and too much fiber can increase your chances of gastrointestinal issues on race day, Nader says. (Pair your simple carbs with a bit of protein to feel more satisfied.)

If all that seems overwhelming, it's also OK to continue your usual eating habits. Carb-loading isn't for everyone, and there's some evidence it doesn't work quite as well for women as for men, Nader says.

Read more: Are Protein Shakes Good for You After Running?

Keep your last evening meal simple and familiar: "Always stick with what you've tried beforehand," Nader says. Practice your pre-race dinner before long training runs to get an idea of what works best for you.

Most runners do well with simple carbs — white pasta, potatoes or rice — along with a lean protein like chicken or salmon, prepared without a creamy sauce (think marinara, not alfredo). Limit fat, which digests slowly; you want your digestive system cleared out before the race. Adding veggies fills you up and provides you with a last, heaping helping of anti-inflammatory antioxidants.

Anxiety can make pre-race eating difficult. But if you can calm your gut enough to stomach breakfast, it's a good idea to do so. The calories you consume in the morning will power you through the early miles, Nader says.

Again, avoid anything new you haven't eaten regularly before running. Experiment with simple, low-fiber carbs and a small amount of protein and fat to fill you up. Think oatmeal with cinnamon, a bagel with nut butter and banana, or an English muffin with jam or honey.