The marathon is a tricky beast. You can nail your training plan, rack up the miles, feel invincible, and get the best super shoes, only to have it all come crashing down on race day because of one critical mistake: a poor fueling strategy for marathon.
I learned this the hard way during my first marathon.
My legs were ready, my endurance was there, but my fueling strategy? Let’s just say I hit the wall hard—right at the 25-kilometer mark.
All those months of training couldn’t save me from adding a brutal 20 minutes to my finish time.
If only I knew then what I know now.
So, let’s rewind the clock four months before that race, as I walk you through everything I wish I had done differently—lessons that could have not only saved me those 20 minutes but shaved off even more.
Fueling Strategy for Marathon
You might be wondering why we’re zooming back four months before race day when we’re talking about race day fueling. The answer? You’ve got to train your gut—just like you train your legs—to handle more fuel before running.
Related: Research Behind the 80/20 Rule in Running
Train Your Gut Before Race Day
If you’re like most runners (and like I used to be), your routine probably involves early morning runs done on an empty stomach or maybe just a light snack.
Let’s be honest—I was playing it safe, avoiding the dreaded mid-run stomach issues. But here’s the twist: I had it all wrong.
It turns out you can actually train your gut to handle more food before running. While not everyone’s gut might be fully “trainable” (and yes, I get the skepticism), it’s all about figuring out what works for you and then practicing it during training.
You can’t expect your stomach to suddenly cooperate with sports nutrition on race day if you haven’t conditioned it beforehand.
Makes sense, right?
The same goes for how close to race time you can eat. Practice gradually closing that gap during your training and observe how your stomach responds.
So, by training your gut, you’ll be primed and ready to toe the start line with a fully loaded tank—giving you the fuel you need to power through.
To nail this, I developed a gut-training plan that made all the difference before my first marathon.
How to Tolerate Food Before Running
Let’s start small. The first step is to sip on a glass of fruit juice about 20 minutes before each run. I actually picked up this tip from dietitian Stephanie Hnatiuk when we had a chat.
This is perfect for those who struggle to eat anything before a run but want to take that first step toward building tolerance.
After you can handle the juice for a week, the next level is blended smoothies. This is where things get a bit thicker and more nutrient-packed.
Test this out for a week. If you hit any bumps (like stomach issues), scale back the portion and give it more time.
Here’s how I progressed through the following weeks:
- Week 1: Start with a smoothie.
- Week 2: Add a piece of bread to your smoothie routine.
- Week 3: Keep the bread, reduce the smoothie a bit, and throw in a piece of fruit.
- Week 4: Add a spread to your bread (peanut butter, anyone?).
- Week 5: Include a muesli bar of your choice.
This gradual build-up is all about prepping your body to hold that full tank of fuel when you hit the start line.
Next, we’ll dive into how to train your gut to handle carbs mid-race…
Train Your Gut for Carbs Mid-Race
One of my biggest rookie mistakes during my first marathon was trying out a race gel for the first time on race day. Big mistake.
I took a mouthful of that sticky stuff and instantly regretted it. It felt like I couldn’t even breathe, let alone digest it. I ended up tossing the gel aside—along with any chance of keeping my energy levels steady.
So not only did I start the race with a half-empty tank, but I also failed to top it up mid-race. No wonder I hit the wall at 25 kilometers!
How to Tolerate Race Gels in a Marathon
If you want to avoid the same fate, you’ve got to train your gut to handle mid-race fuel. Months before race day, use your long runs to practice this.
Start with just a quarter of a gel every 45 to 60 minutes. Once your stomach gets used to that, bump it up to half a gel, and keep progressing until you can comfortably take down a full gel pack.
By the time race day rolls around, your stomach will be battle-tested and ready to handle those gels, ensuring your fuel tank stays topped up when you need it most.
Which brings me to a critical point—the timing of your gels during the race…
Related: Tapering Strategy for Better Marathon Times
When to Consume Gels in a Marathon
A common mistake many runners make is waiting until they feel that dreaded dip in energy levels before reaching for a carb gel.
But by then, it’s already too late.
Here’s why:
First, if you’re already hitting an energy crash, you’ve delayed your carb intake far too long.
Second, once fatigue sets in, your body shifts blood flow toward your working muscles and away from your digestive system.
So, that gel you just consumed? It’s likely to sit heavy in your gut, causing those infamous GI issues that can completely wreck your race.
The key is to be proactive, not reactive.
For most runners, a solid strategy is to take in 30 to 60 grams of carbs every hour, even if you feel fine.
Some runners find it more manageable to split that intake, consuming smaller amounts—say, half a gel—every 30 minutes rather than a full dose every hour. This approach can help keep those stomach issues at bay while ensuring you stay fueled.
Now, you’ve not only trained your gut to handle pre-race fueling but also mastered mid-race nutrition. With consistent energy intake, you’re setting yourself up for a much stronger finish.
Let’s talk about another crucial piece of the puzzle—your hydration strategy…
Related: Research Finds a Good Cadence for Running
Implementing a Hydration Strategy
Fueling up with food is only part of the equation—you’ve got to keep your fluids in check too!
During your race, staying hydrated is key to regulating body temperature, maintaining blood volume, and making sure those vital nutrients get where they need to go.
So how do you get your hydration spot on? It starts with figuring out how much sweat you lose per hour…
Calculating your Sweat Loss
Sweat rates are like fingerprints—everyone’s is unique. Factors like fitness, pace, elevation, temperature, and humidity all play a role in how much you sweat.
So, let’s figure out your sweat loss.
Calculating your Sweat Concentration
You can do it at home or in a lab.
Home Testing
At home, start by weighing yourself right before a run and go for a run. When you finish, dry off, weigh yourself again, and note the difference.
Don’t forget to factor in any fluids you drank during the run.
Repeat this process a few times at different paces, durations, and in varying weather conditions. Over time, a pattern will emerge, giving you a clearer picture of your average sweat loss.
For me, my sweat rate (pic 7.01) is relatively low—around 0.4 to 0.5 liters per hour. To give you some perspective, moderate sweat rates typically range between 0.7 and 1.8 liters per hour.
Ideally, you’d test under race-like conditions—same temperature, humidity, and race-day intensity—but this gives you a solid starting point.
If you want to go beyond just figuring out how much sweat you lose, there’s another layer of accuracy you can explore—testing your sweat concentration at a lab…
Sweat Test Labs
Sweat tests measure how salty your sweat is by determining your sweat sodium concentration. The test is quick and doesn’t even involve exercise—a small sweat sample from your skin is all they need.
For runners, knowing your sweat sodium levels is key because sodium is vital for nerve function, muscle contractions, maintaining blood plasma volume, and keeping your mind sharp—all of which are essential when you’re aiming for peak performance.
When you’re sweating heavily during long runs, especially if you’re someone with a high sweat rate or particularly salty sweat, replacing that lost sodium becomes crucial.
Some sweat test centers even take your sodium results and tailor a hydration plan specific to your training routines, race environments, and conditions.
They provide detailed guidance on what to drink, when, and how much, so you’re fully prepared for any scenario.
How Much Sodium Do We Sweat?
The amount of sodium you lose while sweating is largely determined by genetics, meaning everyone’s sweat has a unique salt concentration. That’s why the one-size-fits-all hydration advice doesn’t always work.
Wondering if getting your sweat tested might be worth it? Ask yourself these questions:
- Do you notice white streaks on your clothes or skin after sweating?
- Do you crave salty foods during long runs or races?
- Do you tend to cramp or feel wiped out after intense sweating?
- Do you think you have a high sweat rate?
- Do you have a demanding training load or tackle long races?
- Do you often train or race in hot conditions?
- Has your performance ever suffered because your hydration strategy felt off?
If you said yes to any of these, a sweat test might help optimize your performance by tailoring your hydration strategy to your specific needs.
For those who lose more sodium in their sweat, simply drinking water won’t be enough—you’ll need to include electrolyte drinks to stay properly balanced.
I got tested a few years ago and found out I’m a pretty salty sweater, losing around 1269 milligrams of sodium per liter of sweat!
With that info and knowing my sweat rate, I was able to dial in a hydration strategy that keeps everything in check on race day.
My Fluid Replacement Strategy
Let’s say I’m losing about 500 ml of sweat per hour—that means I’m also losing roughly 600 milligrams of sodium.
To keep everything in check, I need to replace both the fluids and sodium in the same concentration during the race. This helps keep my electrolytes in check, ensuring everything runs smoothly.
Resistant Starch Products: A Hydration Breakthrough
There’s also some exciting new research on boosting hydration. Products like PREPD, which feature a prebiotic called resistant starch, can be game-changers.
When taken 10 hours before your race, they help your gut absorb water more effectively, holding onto it longer.
The result? Research has confirmed you stay hydrated better and perform stronger.
By taking this before your race, you won’t need to adjust your hydration strategy mid-race—just stick to your plan and enjoy the benefits.
Now, I’m about to share a bonus tip on race-day GI issues, but let’s recap first…
You’ve got the right fueling strategy to start strong and stay strong, and you’re equipped with a fluid replacement strategy that’ll keep your body cool and ready to perform.
But as I mentioned earlier, even with perfect training prep, GI issues can still sneak up on race day…
Stomach Problems On Your Run
You might nail your gut training and build up a solid tolerance during those long runs, but then—bam!—race day hits, and suddenly those dreaded GI issues make an unwelcome appearance.
We’ve all been there—or at least most of us. That sudden “uh oh” moment mid-run that has you frantically scanning for the nearest bathroom. If you haven’t experienced this, consider yourself one of the lucky ones.
The truth is, our bodies—and our stomachs—are all unique, but there are a few common culprits behind those gut troubles when it comes to running…
Blood Flow
Under normal circumstances, your digestive system enjoys a steady supply of blood, keeping everything running smoothly.
But when you lace up and start exercising, your cardiovascular system prioritizes your working muscles, diverting blood and oxygen away from digestion.
This redirection can put your gut on pause, leading to that all-too-familiar urge to find a bathroom in the middle of your run.
Then, you’ve got vibration…
Vibration
Let’s be real—running isn’t exactly a smooth ride. Even if you have the most graceful stride, there’s still a lot of bouncing up and down. While your bones and cartilage absorb most of the impact, your stomach isn’t as lucky.
All that jostling puts extra pressure on your gut and intestines while sloshing your stomach acid around. When you mix these factors together, it’s no surprise your tummy isn’t thrilled.
On top of blood flow and vibrations, let’s talk about hormones…
Hormones
Yes, running ramps up cortisol, the hormone partly responsible for that runner’s high we all love. Unfortunately, cortisol also impacts other systems in our bodies, including digestion.
And if you’re gearing up for a race or big session, adrenaline joins the party, creating a cocktail that’s not exactly friendly to your gut.
For women, hormonal fluctuations during the menstrual cycle can make the stomach more sensitive, and running often exacerbates this discomfort.
If that sounds like you, it’s crucial to focus on controlling the factors you can manage.
Now, what can you do to prevent these issues? Let’s dive in…
How to Stop Stomach Issues from Ruining Your Run
Diet
Diet is the most obvious factor affecting your stomach, and it’s especially crucial for runners. We all know that what we eat impacts our digestive system, and running can exacerbate these effects.
Certain foods—like dairy products, sugary treats, and some fruits and vegetables—can upset your stomach. Consider cutting back on these or at least reducing their intake to see if it helps.
Your gut health is influenced not only by your diet but also by factors like antibiotics and other uncontrollable aspects.
An unhappy gut microbiome struggles more with digestion, which can lead to stomach issues during your runs.
Exploring prebiotics and postbiotics might be beneficial. Emerging evidence suggests they can support a healthier gut microbiome, which could alleviate general stomach issues and improve your running experience.
I’ve dabbled with these in the past, but it’s wise to research thoroughly before starting any new supplement. Some products may look promising but fail to reach the important parts of your gut due to stomach acid.
Timing
Timing plays an important role in preventing stomach issues during your run. Everyone’s digestive system is unique, so there’s no one-size-fits-all rule, but some general guidelines can help.
For most people, it’s wise to avoid having a large meal within three hours of your run. This gives your body enough time to digest and minimize any discomfort. For snacks, aim to eat no closer than 30 minutes before you start.
However, these guidelines can vary based on factors like the amount and type of food you’re consuming, and the intensity of your run.
For instance, you might tolerate a larger meal before a leisurely jog compared to a high-intensity threshold training session. Listen to your body and adjust accordingly to find what works best for you.
Hydration
Hydration is a delicate balance when it comes to running. On one hand, drinking too much water can lead to discomfort, such as a side stitch or a sloshing sensation in your stomach, which can disrupt your run.
On the other hand, not drinking enough fluid can result in more severe issues like diarrhea, vomiting, or feeling unwell, which in turn can exacerbate dehydration and create a vicious cycle.
The key is to start your run or race well-hydrated—not just with water but with electrolytes as well.
Develop a hydration strategy that ensures you’re topping up consistently throughout your run, adjusting for the conditions and intensity.
Avoid large quantities at once to prevent stomach cramps, and aim for regular, smaller sips to keep your body in balance.
Psychological Stress
Anxieties and nerves can wreak havoc on your digestive system, making it harder for your gut to handle the food you’ve been training with.
If you’re feeling jittery on race day, your gut might struggle with processing food, leading to discomfort and stomach issues.
To manage this, incorporate breathing exercises, meditation, or cognitive strategies to calm your nerves.
Keeping your mental state in check can help maintain digestive stability and ensure you’re ready to perform at your best.
If you’ve tried everything and still face persistent stomach issues during runs, seeking advice from a professional might be your next step for personalized guidance.
Now that you can master your marathon fueling, don’t miss out on another performance booster—coffee. It just might turn your daily cup into your secret weapon on race day!”
But now, I’m turning it over to you. What’s worked for you in keeping those gut troubles at bay? Share your tips and experiences so we can all enjoy smoother, more comfortable runs!
So there you have it. Good luck with your marathon and let me know if you found this article helpful.
