3 Things I Would Do If I Were Starting My Marathon Journey Again to Avoid GI Distress
Training for a marathon is one of the most exciting and challenging journeys a runner can embark on. However, for many, it can also come with some unexpected and frustrating hurdles—especially when it comes to gastrointestinal (GI) distress. If you’ve been on a run only to find yourself sprinting toward the nearest restroom instead of the finish line, you’re not alone.
When I first started marathon training, I faced my fair share of GI issues: stomach cramps, unexpected bathroom emergencies, and the dreaded "runner’s trots." While it’s tempting to chalk these up as just part of being a runner, I’ve learned through experience—and from working with clients—that this doesn’t have to be your reality.
Here’s what I wish I’d known from the start: GI issues are common, but they’re not inevitable. By understanding your body, adjusting your nutrition, and training smarter, you can minimize discomfort and focus on what you love—running.
In this blog, I’ll walk you through the three things I’d do differently if I were starting my marathon training journey again. These tips are designed to help you identify and address the root causes of GI distress so you can perform your best on race day.
Don’t let GI Issues be the reason you can’t cross the
finish line!
Why GI Distress in Runners Happens: A Quick Primer
Before we dive into the solutions, let’s talk about why GI issues occur during endurance running. GI symptoms like cramps, nausea, diarrhea, and bloating are often caused by a combination of:
Reduced blood flow to the gut: During intense exercise, your body prioritizes sending blood to working muscles, which can slow digestion.
Mechanical stress: The repetitive motion of running can jostle your stomach and intestines, exacerbating symptoms.
Nutritional factors: Certain foods, beverages, or fueling strategies can irritate the gut or be poorly absorbed during exercise. Other factors that are not often considered are the day to day dietary choices that can lead to more complex GI issues.
“Studies suggest that 30–50% of endurance athletes experience GI symptoms during training or races. While some cases are mild, others can significantly impact performance—or even cause runners to drop out of races.”
Tip #1: Prioritize Your Overall Diet
Your everyday nutrition lays the foundation for how well your body performs during training. When I started running marathons, I didn’t pay enough attention to my day-to-day diet, which led to poor gut health and inconsistent energy levels. I was confused by all the information out there and was ultimately under-fuelling and missing key nutrients that took some time to repair.
Here’s what I’d do differently:
Increase Variety in Your Diet
Eating a wide range of foods, particularly carbohydrates, vegetables, and fruits, introduces diverse nutrients and prebiotics that support a healthy gut microbiome. A strong gut with a healthy and diverse microbiome can better handle the physical and nutritional stress of long runs.
Example:
Instead of sticking to plain pasta or rice, experiment with quinoa, farro, or sweet potatoes as your carbohydrate sources. Add colorful veggies like spinach, carrots, and bell peppers to meals for a fiber boost.
Track How Foods Affect You
Start a food and symptom journal to identify patterns. Write down what you eat, when you eat it, and how it makes you feel during and after runs. This can help pinpoint foods that might be triggering GI symptoms.
Introduce Fiber Gradually
While reducing fiber intake is common advice before race day, it’s important to consume adequate fiber during training to promote regular digestion. Slowly increase your fiber intake over several weeks to avoid overwhelming your gut.
Pro Tip: Aim for whole-food sources like oats, berries, and legumes, and drink plenty of water to support digestion
Foods higher in fibre will support a healthy gut microbiome that can prevent GI issues longer term.
Tip #2: Master Your Race-Day Fueling Strategy
If I could go back, I’d spend much more refining my fuelling strategy. I learned very early on that I have a strong aversion to gels, it’s a texture thing for me and I just can’t do them. Early on in my marathon journey, this resulted in a lot of under-fuelled runs, while I tried to find alternatives that did work for me. Which meant that I did a lot of experimenting!
Read the Labels on Sports Nutrition Products
Pay close attention to the ingredients in your gels, chews, and electrolyte drinks. Look for potential culprits like artificial sweeteners, high-fructose corn syrup, or dyes, which can irritate sensitive tummies.
Quick Tip: Many runners find success with isotonic gels or products made with maltodextrin, as these tend to be easier on the stomach.
Experiment Early and Often
Test your fueling plan during training runs—not just before the marathon. Experiment with different products, timing, and quantities to see what works best for your body, this should be happening throughout your training season because nutrition is so individual and what works for one person, may not work for you, but you need to find that out and preferably not on race day!
Example Schedule for a Long Run:
Pre-run: A banana with peanut butter 2 hours before.
During run: One energy gel every 30 minutes with a few sips of water and alternate with electrolytes.
Hydrate Correctly
Dehydration can amplify GI issues, particularly when combined with sugary gels. Aim to drink small amounts of water consistently during your runs, rather than chugging large amounts all at once, because chugging can lead to the sloshy feeling or side stitches.
Pro Tip: If you know you are a heavy sweater, or you’re training in hot-weather, consider carrying a sports drink with electrolytes and water to replace sodium and prevent cramping.
Train your tummy
Training your tummy is just as important as training your legs. Over time, you can improve your body’s ability to digest and absorb fuel (aka. carbs) during exercise. Here’s how:
Practice Eating During Runs: Start with small amounts of food or drink and gradually increase to simulate race-day conditions.
Choose the Right Carbohydrates: Glucose-fructose combinations are often better tolerated than pure fructose. Note that there are a lot of fuels on the market these days, but you can also use basic gas-station candy and real food too (check out my blog post on Real Foods To Fuel Your Runs).
Be Consistent: Aim to train with the same products you plan to use on race day to avoid surprises. Which is why it’s so important to start testing early on in your training season.
Some of my favourite brands for pre-fuelling on the go, electorlytes and carbs to fuel my long runs and races.
Tip #3: Seek Expert Support
If you’re struggling with GI issues despite your best efforts, it might be time to work with a professional. I spent far too long trying to figure it out on my own, and it wasn’t until I sought guidance that I truly started to see progress.
How a Nutritionist Can Help
A nutrition expert can help you:
Pinpoint triggers through detailed food and training logs.
Develop a personalized fueling plan tailored to your unique needs.
Help train your gut to better tolerate food and fluids during exercise.
DIY vs. Professional Guidance
While trial and error can get you part of the way, a working with a nutritionist can save you time, energy, and frustration. If you’re serious about achieving your goals, don’t hesitate to invest in support.
“Client Success Story:
One of my clients, Sarah, was ready to give up on training for her first marathon because of persistent stomach cramps. After just our very first session, we identified that her pre-run snacks were too high in fat, slowing her digestion. By switching to a carb-based snack and adjusting her hydration strategy, she was able to complete her training runs comfortably—and crushed her first marathon!”
Final Thoughts: You Don’t Have to Run Alone
Running a marathon is an incredible achievement, but the journey doesn’t have to be filled with discomfort and uncertainty. By focusing on your diet, refining your fueling strategy, and seeking support when needed, you can set yourself up for success—not just on race day, but throughout your entire training journey.
If you’re ready to tackle GI distress head-on, I’d love to help. Click here to learn more about my personalized nutrition coaching and how we can work together to get you running stronger and feeling better.
Happy running!
7 Day Meal Plan for Runners
If you’re looking for a little meal inspiration to fit your training plan, find my 7 Day Plan for Runners here.
