Are you carb loading correctly before your marathon, or could your race-week nutrition be setting you up to hit the dreaded wall at mile 20?

 

You’ve probably heard the classic advice: Eat a giant bowl of pasta the night before your marathon, and you’ll be ready to go!

 

But here’s the problem: Carb loading isn’t about one big pasta dinner. It’s about strategically increasing your carbohydrate intake in the days leading up to your race so your muscles have the energy they need to perform.

 

 

 

 

As a running physical therapist and coach, I’ve worked with hundreds of runners who have put months into their marathon training, only to struggle on race day because their fueling strategy wasn’t dialed in.

 

You can have the perfect training plan, complete every long run, and feel incredibly fit. But if you arrive at the starting line with inadequate glycogen stores, you’re making those 26.2 miles harder than they need to be.

 

In Episode 308 of the Healthy Runner Podcast, I’m joined by my good friend and registered dietitian, Brooke Czarnecki, RDN, LD, to break down how to carb load before a marathon, what foods to eat, when to start, and the common mistakes runners should avoid.

 

Whether you’re preparing for your first marathon or chasing your next personal record, this guide will help you approach race-week nutrition with a smarter plan.

 

 

Are You Carb Loading Wrong? Running Dietitian Exposes the Biggest Mistakes

 

 

 

 

 

What Is Carb Loading, and Why Does It Matter for Marathon Runners?

 

 

Carb loading, also called carbohydrate loading, is a nutrition strategy designed to maximize the amount of glycogen stored in your muscles before an endurance event.

 

Think of glycogen as your body’s stored carbohydrate fuel.

 

When you’re running a marathon, your body uses a combination of carbohydrates and fat to produce energy. As your running intensity increases, carbohydrates become especially important.

 

The challenge?

 

Your body can only store a limited amount of glycogen.

 

When those stores become significantly depleted, maintaining your marathon pace can become increasingly difficult.

 

That’s one reason runners may experience the dreaded wall late in a marathon.

 

Carb loading helps you begin your race with fuller glycogen stores, giving you more available carbohydrate energy for the miles ahead.

 

However, proper carb loading is only one part of the equation. Your training, pacing, hydration, and fueling during the race also play important roles.

 

Coach Duane’s Take: You wouldn’t start a long road trip with a half-empty gas tank. Your marathon deserves the same preparation. Make sure you’re giving your body the fuel it needs before you even reach the starting line.

 

 

1. Why Do Marathon Runners Hit the Wall at Mile 20?

 

 

You’ve probably heard runners talk about hitting the wall.

 

Everything feels great for the first 15 or 18 miles. You’re holding your goal pace, your breathing feels controlled, and you’re starting to imagine that finish line.

 

Then suddenly, your legs feel incredibly heavy, your pace drops, and every mile becomes a battle.

 

What happened?

 

One possible explanation is glycogen depletion.

 

When your available carbohydrate stores become too low, your body has difficulty sustaining the same running intensity.

 

However, hitting the wall isn’t always caused by nutrition alone.

 

Other contributing factors can include:

-Starting the race faster than your fitness supports.

-Inadequate marathon-specific training.

-Insufficient carbohydrate intake during the race.

-Heat, dehydration, or other environmental stressors.

-Beginning the race with inadequate glycogen stores.

 

This is why your marathon fueling strategy needs to begin well before race morning.

 

Carb loading helps maximize your starting glycogen stores, while consuming carbohydrates during the race helps maintain carbohydrate availability as you run.

 

The goal isn’t to rely on one strategy. It’s to combine proper training, smart pacing, and effective fueling.

 

 

2. The Biggest Carb-Loading Mistake: Relying on One Pasta Dinner

 

 

Let’s talk about one of the most common misconceptions I hear from runners.

 

“I’m carb loading tonight. I’m having a huge bowl of pasta!”

 

Now, there’s nothing wrong with pasta. It can be an excellent carbohydrate source for runners.

 

But eating one enormous meal the night before your marathon isn’t the same as following a structured carb-loading plan.

 

Your body needs adequate carbohydrate intake over time to maximize muscle glycogen stores.

 

Trying to cram everything into one meal can also leave you feeling overly full, bloated, or uncomfortable on race morning.

 

Instead of focusing on one massive dinner, think about spreading your carbohydrate intake throughout the day over the final days before your race.

 

This might include carbohydrate-rich meals, snacks, and drinks that are familiar to your digestive system.

 

The takeaway: Carb loading is a multi-day nutrition strategy, not a last-minute eating contest.

 

 

3. When Should You Start Carb Loading Before a Marathon?

 

 

One of the biggest questions runners have is whether they should begin carb loading 24, 48, or 72 hours before their marathon.

 

For many marathon runners, a structured carbohydrate-loading period of approximately 36–48 hours can be effective, while some individualized plans begin around three days before the race.

 

The exact timing depends on your carbohydrate targets, training taper, gastrointestinal tolerance, and individual needs.

 

During this period, your running volume is typically reduced as part of your marathon taper.

 

This combination of reduced training demands and increased carbohydrate availability helps your body build glycogen stores.

 

For endurance events lasting longer than approximately 90 minutes, established sports nutrition guidance often recommends carbohydrate-loading targets of around 10–12 grams of carbohydrate per kilogram of body weight per day for 36–48 hours.

 

However, that is a substantial amount of food, and not every runner needs or tolerates the same approach. A sports dietitian can help you determine an appropriate target.

 

The important point is to plan ahead rather than waiting until the night before your race.

 

 

4. What Should You Actually Eat Before a Marathon?

 

 

Knowing you need more carbohydrates is one thing.

 

Figuring out what to put on your plate is another!

 

During carb loading, the goal is to increase carbohydrate intake using foods you already know work well for your body.

 

Breakfast

Bagels, toast, pancakes, cereal, oatmeal, or other familiar carbohydrate-rich foods.

 

Lunch and dinner

Pasta, rice, potatoes, bread, and other carbohydrate-rich foods alongside moderate portions of protein.

 

Snacks

Pretzels, bananas, applesauce, crackers, granola bars, or other easy-to-digest carbohydrate sources.

 

Drinks

Sports drinks or other carbohydrate-containing beverages can help some runners meet their targets without relying entirely on solid food.

 

You may also benefit from temporarily reducing high-fiber foods and very large, high-fat meals if they tend to cause gastrointestinal discomfort.

 

That doesn’t mean every runner needs to eliminate vegetables, fiber, or fat.

 

It means choosing familiar foods and adjusting portions based on what your digestive system tolerates.

 

And remember: Race week is not the time to experiment with unfamiliar foods!

 

 

5. Can You Train Your Gut to Handle More Carbohydrates?

 

 

Here’s something many runners overlook.

 

Even if you carb load perfectly before your marathon, you still need to fuel during the race.

 

For longer endurance events, runners commonly work toward consuming approximately 60–90 grams of carbohydrate per hour, depending on race duration, intensity, product composition, and individual tolerance.

 

But what if every time you try to take in more gels or sports drinks, your stomach rebels?

 

That’s where gut training comes in.

 

Just like you gradually train your muscles to tolerate longer runs, you can practice consuming carbohydrates during training to improve your tolerance of a race-day fueling plan.

 

Start with an amount you can comfortably handle during your long runs and gradually practice your intended race-day intake.

 

Experiment with:

-Different carbohydrate sources and sports nutrition products.

-The timing and frequency of your fuel.

-Taking smaller amounts more frequently.

-Drinking appropriate amounts of fluid with your fuel.

 

The goal is to establish a repeatable strategy before race day.

 

Coach Duane’s Take: Your long runs aren’t just about building endurance. They’re also opportunities to practice the exact fueling strategy you’ll use during your marathon.

 

 

6. Is Eating So Many Carbohydrates Before a Marathon Healthy

 

 

For runners who typically eat a balanced diet, suddenly increasing carbohydrate intake can feel uncomfortable.

 

You might wonder whether consuming hundreds of grams of carbohydrates over several days could negatively affect your blood sugar or long-term health.

 

Here’s an important distinction.

 

A short-term carbohydrate-loading strategy designed to support an endurance event is different from your everyday nutrition pattern.

 

Carbohydrates are an essential energy source for endurance performance, and increasing intake before a marathon can support glycogen storage.

 

However, carbohydrate needs and blood glucose responses vary between individuals.

 

Runners with diabetes or other conditions affecting glucose regulation should develop an individualized fueling plan with their healthcare team and a qualified sports dietitian.

 

Carb loading isn’t about eating unlimited carbohydrates or ignoring your health.

 

It’s about matching your nutrition to the demands of your upcoming event.

 

 

7. Should Female Runners Carb Load Differently?

 

 

Female runners sometimes wonder whether their carb-loading strategy needs to change based on their menstrual cycle or hormonal fluctuations.

 

While hormonal changes may influence aspects of metabolism, current evidence does not support a single menstrual-cycle-based carb-loading protocol that applies to every female runner.

 

Individual energy needs, training demands, gastrointestinal tolerance, and overall carbohydrate availability are important considerations.

 

One particularly important issue is making sure you’re eating enough throughout marathon training.

 

Chronically underfueling can affect recovery, training adaptations, and overall health.

 

If you’ve spent months consistently underfueling, a few days of carb loading won’t address all the consequences.

 

This is where individualized guidance from a sports dietitian can be especially valuable.

 

 

8. Your Marathon Is Three Days Away. What Should You Do Now?

 

 

Imagine this scenario.

 

Your marathon is this weekend, and you’ve just realized you haven’t been following a carb-loading plan.

 

Is it too late?

 

Not necessarily.

 

You still have time to organize your nutrition, but the key is to avoid panicking or suddenly forcing yourself to eat enormous amounts of unfamiliar food.

 

Here’s a practical framework for the final three days.

 

 

Your 3-Day Carb-Loading Checklist

 

 

General preparation framework — individual carbohydrate targets should be personalized.

 

-Establish your carbohydrate target and meal plan.

-Shop for familiar, carbohydrate-rich foods.

-Spread carbohydrates across meals and snacks.

-Reduce excessive fiber or fat if they trigger GI symptoms.

-Maintain appropriate hydration without overdrinking.

-Prepare your race-morning breakfast and on-course fuel.

-Most importantly, don’t use race week to introduce an entirely new nutrition routine that you haven’t tested.

 

If you’re unsure how to calculate your carbohydrate needs or have a history of gastrointestinal problems, working with a registered dietitian can help you create a more personalized strategy.

 

 

The Bottom Line: Your Marathon Fueling Starts Before Race Morning

 

 

If there’s one thing I want you to take away from this episode, it’s this:

You can’t expect your body to perform at its best for 26.2 miles if you haven’t given it the fuel it needs.

 

Proper carb loading isn’t about eating as much pasta as possible the night before your race.

 

It’s about developing a thoughtful nutrition strategy, beginning early enough, choosing familiar foods, and practicing your fueling during training.

 

Your marathon success comes from putting all the pieces together: your run plan, strength training, nutrition, recovery, mindset, and race strategy.

 

You’ve already put in the hard work of training.

 

Now make sure your nutrition supports it!

 

 

Listen to Episode 308 of the Healthy Runner Podcast

 

 

Carb Loading Before a Marathon: What Most Runners Get Wrong with Brooke Czarnecki, RDN, LD

 

Join Brooke and me as we answer common marathon nutrition questions and discuss how to approach carb loading before your next race.

 

You can also learn more about Brooke and her work as a registered dietitian and endurance sports nutrition expert through her guest biography .

 

And if you want to continue learning about race-day nutrition, check out Episode 235: Optimizing Summer Hydration While Running .

 

Here’s to healthy running!

 

 

 

She went from Chronically Underfueled with Constant Injuries to Running her First Marathon!

 

Struggling with nagging injuries such as knee pain or plantar fasciitis and you thought you would never run pain free again?  Do you feel so lethargic and tired because you are not getting the proper amount of nutrition to fuel the amount of exercise you do on a daily basis?

 

Those were the things Rachel was struggling with prior to getting guidance with myself as her running Physical Therapist/coach and Brooke Czarnecki as her running Registered Dietitian at Spark Healthy Runner.  Listen to what she discovered that changed her training forever…

 

Watch Now!

 

 

Want a Personalized Marathon Nutrition and Training Plan?

 

 

Every runner is different.

 

Your training history, injury history, nutrition needs, race goals, and lifestyle all influence what your ideal marathon preparation should look like.

 

If you’re looking for individualized guidance to dial in your nutrition, build strength, overcome injuries, and run your next race with confidence, our Healthy Runner Coaching program and Healthy Runner Academy can help.

 

Our team combines running physical therapy, personalized run coaching, strength training, and sports nutrition expertise to help you become a healthier, stronger runner.

 

Ready to Take the Next Step? Learn More About Healthy Runner Coaching Here!

 

 

Your race-day hydration strategy shouldn’t start on race day! 💦

 

 

 

It’s something you should be practicing during your long runs NOW, especially if you’re gearing up for a fall half marathon or marathon.

 

Trust me, I learned this lesson the hard way.

 

During my first marathon, I cramped up and ended up walking the final 6 miles 😩

 

And I still remember those hot, sweaty long runs when I’d finish completely wiped out and spend the rest of the day as a lump on the couch instead of enjoying time with my family.

 

Over the years, I’ve learned that hydration and fueling deserve just as much attention as our running and strength training.

 

That’s why LMNT has become a staple in my hydration routine.

 

Each stick pack contains:

-1,000 mg sodium

-200 mg potassium

-60 mg magnesium

-Zero sugar or artificial colors

 

As a running physical therapist and coach, one of the biggest lessons I share with my athletes is this:

Nothing new on race day!

 

Use your long runs to figure out your hydration and fueling needs, what works for your stomach, and how much fluid and sodium you need based on your sweat losses and conditions.

 

Remember, electrolytes are one piece of the puzzle. Your carbohydrate fueling and overall hydration strategy matter, too!

 

And I’ve got a special offer to help you get started. 👇🏼

🎁 FREE 8-Count LMNT Sample Pack!

 

Get a FREE sample pack of LMNT’s most popular flavors with any purchase even if you’ve ordered before!

 

Claim Your FREE LMNT Sample Pack Free sample pack with any purchase

 

With fall race season here, now is a great time to dial in your hydration strategy instead of waiting until you’re standing at the starting line.

 

 

Nail your nutrition and run your best

 

Most runners spend an enormous amount of time trying to figure out what to eat before or during a run…

 

We hear it all the time…legs feel heavy…don’t have energy to go for a run, or worse you have to stop your run short because you just can’t go any further…

 

Imagine if you could feel strong during your run because you were eating the right food?

 

Spark Healthy Runner’s Registered Dietitian, Brooke Czarnecki has created an AMAZING resource for you on what you should eat as a runner.

 

 

This blueprint lays out how to fuel as a runner so you don’t have to feel sluggish during your runs or worse “bonk” during a race!

 

Here is what is included: 

 

✅Top 5 Nutrition Tips for Runners

✅ Nutrition Basics for Running

✅ The Ultimate Snack Guide

✅ Long Run Fueling Strategies

 

Claim your Nutrition Blueprint here!

 

 

 

Connect with Brooke:

Learn More About Brooke and get all her previous episodes on the podcast in one place!

Brooke’s Race Day Carb Loading Guide

 

– Instagram: @intentfulnutrition

– Email: intentfulnutrition@gmail.com

– Healthy Runner Facebook Community

– Actively Fueled Podcast on Spotify

 

 

Get my full personal running story here

 

 

 

There are six parts of your running journey that need to be optimized so you can run strong and last long! Learn them here.

 

 

Want these to land in your inbox each and every week so you can learn how to become a stronger, faster, lifelong injury free runner?

 

 

 

 

Subscribe to my weekly newsletter here!

 

Thanks for reading!

 

Yours in health,

Duane

 

 

Connect with Dr. Duane:

 

 

Dr. Duane Scotti, DPT, PhD, OCS is a running physical therapist, run coach, host of the Healthy Runner podcast, and founder of Spark Healthy Runner and has been a leader in the rehab and running community for 20+ years.

 

Duane initially started running as an adult, wanting to add some cardio to his gym sessions. After having hip surgery, his doctor advised him to get off the treadmill and run outside. Without having fully recovered, Duane suffered his first running-related hamstring tendon injury and many others as a novice runner early on.

 

As a coach, he has guided thousands of athletes back to running, finishing their first marathon, crushing a personal best, and even the elusive Boston Marathon qualifying time.

 

After 19 years teaching in higher education, Duane decided to step away as a Clinical Associate Professor of Physical Therapy to pursue his passion educating the running community.  Through his signature 1:1 coaching program, Healthy Runner Academy membership, weekly videos, and podcast episodes, he empowers runners to get stronger, run faster, and enjoy lifelong injury free running without having to stop running to get over an injury.  Dr. Duane truly believes that anyone can run and that all runners should be treated differently when recovering from an injury.  He is on a mission to change the traditional thinking that running causes “overuse injuries” or “your body is just not meant to run” and you must “take a break” to get better.  Through strength and run specific training you can grow a strong mind, strong body, and just keep running!

 

Duane received his Bachelor of Health Science degree and Master of Physical Therapy degree from Quinnipiac University in 2001 and 2003. He then went on to receive a clinical Doctor of Physical Therapy and a Ph.D. in Physical Therapy from Nova Southeastern University in 2017. Duane is a board-certified Orthopaedic Clinical Specialist, RRCA Certified Running Coach, Certified Mulligan Practitioner, certified in dry needling and has advanced training in spinal manipulation and rehabilitation for runners.

 

As an athlete, Duane is an adult-onset runner, 6x marathoner, avid half marathoner, and enjoys challenging himself to learn and grow in his personal running journey!

 

A native New Yorker from Long Island, Duane currently lives in Cheshire, Connecticut with his wife Deb and his two teenage daughters who are competitive volleyball players.  They all love to explore new beaches along the east coast.

 

-Instagram – @sparkhealthyrunner

 

–Join Our Healthy Runner Facebook Community

 

–Subscribe to our YouTube Channel

 

–duane@sparkhealthyrunner.com

 

Get weekly running tips on the Healthy Runner Podcast…available wherever you get your podcasts!