9 Nutrition Mistakes That Can Derail Your Marathon Training

Prepping for a marathon involves more than pounding the pavement. What you eat during training and on race day can make or break your PR. To help you avoid common marathon training nutrition mistakes, train smarter with advice from Nancy Clark, RD, a sports nutrition counselor in Boston and author of Nancy Clark's Sports Nutrition Guidebook.

Don't let all your hard work during marathon training go to waste. (Image: Eva-Katalin/iStock/GettyImages)

1. You Don’t Eat Enough

A lot of marathoners think if they lose weight, they'll be lighter and run faster, says Clark. The problem? Cutting too many calories from your diet leads to low energy. When you don't eat enough, your body doesn't have sufficient fuel to power you through your workouts.

That means you don't have the oomph to log those long miles. To perform your best, Clark recommends either fueling up an hour or so before a run or refueling within an hour after one. And make sure you're getting sufficient calories throughout the rest of the day, too.

Learn how to fill your plate with healthy, nutrient-dense foods by logging your meals on the MyPlate app. Download now to fine-tune your diet today!

2. You Overeat

Conversely, training for a marathon doesn't give you license to devour a stack of chocolate chip pancakes (and whipped cream!) every day. We know what you're thinking: "But I just logged 16 miles!"

Here's the problem: Outside of training, you're likely moving very little the rest of the day, says Clark, who's referring to sedentary athlete syndrome. Basically, it's the idea that the average exerciser or recreational athlete leads a very sedentary lifestyle beyond their workouts.

So, if you're stuffing your face with food after a long run and sitting 23 hours a day, you're probably ingesting more calories than you burned, which may lead to weight gain. To nip your appetite in the bud and stave off cravings for sweets, Clark recommends eating a combination of healthy carbs and protein (more on this later!) within an hour of your run.

3. You Skip Breakfast

Going for a short run? You might be fine skipping breakfast, but come marathon day, you can't race on an empty stomach. Here's why: When you don't eat before you exercise, your blood sugar drops and you won't have the pep to push through a long run, says Clark.

Plus, logging lots of miles on low energy is miserable — you'll feel exhausted, grumpy and lightheaded — and an ineffective training strategy. To run at your fastest, Clark recommends consuming between 100 and 300 calories of carbs before you hit the road to get your blood sugar on the up swing.

4. You Don’t Hydrate

During a marathon, one of your main concerns should be to prevent dehydration, says Clark. Dehydration not only slows your performance, but also delays your recovery. That's why it's important to calculate about how much you sweat so you know the exact amount of H2O you need to replenish those lost fluids.

So how do you figure out your sweat rate? Without drinking anything, weigh yourself before and after an hour-long run. If you lose two pounds of water, that's equivalent to one quart, meaning you should drink eight ounces every 15 minutes. By keeping your fluid goal in mind, you'll learn to properly rehydrate during training, and thus be ready to rock on race day.

5. You Don’t Fuel During Long Runs

On top of staying hydrated, maintaining a normal blood sugar level is your other primary goal during the race, says Clark. Remember, when your blood sugar dips, so does your energy. And on race day, you can't afford to peter out midway — you need enough gas in your tank to take you through mile 26.

In addition to eating before your workouts, you should be fueling throughout your long runs, too. You're likely to burn through your breakfast calories within an hour or so, but Clark recommends eating before you feel hungry. Depending on your size, you should aim to consume 200 to 300 calories an hour to keep your body working at its peak.

What does a mid-race snack look like? You need carbs for fuel — gels, sports drinks, power bars or dried fruit all do the trick. But what kinds of food you eat depends on what your body can tolerate, says Clark. "Part of the training is learning what foods will work for you during the long run," says Clark, who also suggests researching the race's website in advance to see the fueling options that will be available on the course.

6. You Don’t Refuel Properly After Runs

Addicted to your post-run protein shake? Your body needs more than just protein for proper recovery during marathon training. After you run, you should eat a meal with a 3:1 carb-to-protein ratio, says Clark. Carbs like fruits, vegetables and whole grains refuel the muscles while protein builds and repairs them.

Chocolate milk is an excellent post-run food, since it has the right balance of carbs and protein. Likewise, Clark recommends spaghetti and meatballs, chicken and rice or a peanut butter and jelly sandwich to enhance your recovery process.

7. You Don’t Carb Load Before the Race

Pre-race pasta dinners are a staple for marathoners. That's because a healthy store of carbs provides energy to complete all 26.2 miles. Just be sure you're not overdoing it on too many processed carbs, says Clark, who explains that too much white bread, bagels and pastas might clog you up and lead to constipation.

On the other hand, carb-loading with unprocessed, high-fiber foods like dates and figs can aggravate your stomach and cause loose stool.

To find the right balance, experiment with different fueling options during training, so come race day, you know exactly what types of carbs — and foods in general — work for you, says Clark. Essentially, you need to practice your eating — and train your intestinal tract — just as you do your stride.

8. You Eat Something Unfamiliar on Race Day

"More marathons are won or lost in the portable toilets than at the dinner table," says Clark quoting the marathon legend, Bill Rodgers. In other words, bowel issues and intestinal problems are a major concern for runners, and consuming something your body's not used to may cause a torrent of stomach issues.

On race day — and the days leading up to it — you want to stick to eating with what's tried and true, says Clark. That means nothing new on race day. By that point, you should know what types of foods your stomach can handle and which will help you run your best. So, if spaghetti works for you, don't suddenly try quinoa the night before.

And if you're traveling to a marathon, research your dining options ahead of time, so you can find the perfect spot for your pre-marathon meal. A little planning will go a long way when it comes to your performance on race day.

9. You Hit the Pub After the Race

You crushed your PR and now it's time to celebrate at the bar, right? Hold your horses! If you're drinking on an empty stomach and you're dehydrated, a little liquor will hit you like a ton of bricks, says Clark. Plus, alcohol can impair your recovery process, according to a July 2014 study in Sports Medicine.

If you're going to toss a couple back, first drink a few glasses of water and eat something with carbs to coat your stomach, says Clark. And beer may be a smarter post-race cocktail choice because of its higher water content. That said, if you can, skip the booze. There's nothing greater than a natural runner's high.

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