You’ve put in the training. Your legs feel strong, your mindset is focused, and race day is just around the corner. But there’s one thing you’re still worried about—your gut.
If you’ve ever experienced stomach cramps, nausea, or an urgent bathroom stop mid-run, you know how disruptive gastrointestinal (GI) distress can be for endurance athletes.
These digestive issues are common, but they don’t have to be inevitable. Whether you’re preparing for a marathon, long-distance triathlon, or your next ultra, understanding what causes runner’s stomach and how to prevent it can be a game-changer for both performance and peace of mind.
This blog post will break down the causes of GI distress during exercise, explain the science of gut training, and offer actionable tips to help you fuel more comfortably. Let’s get started.
What Is Runner’s Stomach and Why Does It Happen?
If you’ve ever found yourself doubled over with cramps mid-run or sprinting to the nearest porta-potty during a race, you’re not alone.
These unpleasant symptoms are often signs of what’s commonly known as runner’s stomach — a form of gastrointestinal (GI) distress that impacts endurance athletes of all levels.
Runner’s stomach refers to a range of digestive symptoms that occur during or after intense or prolonged exercise, including:
- Nausea
- Bloating
- Cramping
- Gas
- Diarrhea
- Vomiting (sometimes)
While it’s most commonly associated with running, athletes in triathlon, cycling, and ultrarunning also report similar issues.
It can be discouraging to train hard for weeks or months only to have your race derailed by digestive discomfort. Many athletes accept these symptoms as inevitable, but in most cases, they can be significantly reduced or even eliminated with the right strategies.
Understanding why this happens is the first step toward managing and eventually preventing these symptoms.
Let’s explore the connection between exercise and digestion in more detail.
Exercise and Digestion: The Science Behind GI Distress
When you’re working hard during a training session or race, your body diverts blood flow away from your digestive system and toward your muscles and skin (to support performance and cooling).
This can slow down or impair digestion, setting the stage for GI distress.
Other factors also come into play, including:
- Mechanical jostling: The repetitive bouncing during running can physically shake your digestive tract, especially when food or fluid hasn’t been fully absorbed.
- Dehydration: Without enough fluid, the stomach may empty more slowly, increasing the risk of nausea and cramping.
- Stress: Race-day nerves can stimulate the gut, sometimes causing urgent bathroom trips.
- Heat and humidity: These can increase gut permeability, leading to symptoms like diarrhea and cramping.
- Hormonal shifts: Particularly in female athletes, menstrual cycle phases can influence gut motility and discomfort.
The link between exercise and digestion is complex, but it can be manageable. Awareness is key, and small changes can lead to big improvements.
The more you understand about your body’s response to endurance exercise, the more empowered you are to adapt and prevent issues.
Common Causes of Exercise-Induced Gastrointestinal Distress
While each athlete’s experience is unique, some common triggers frequently contribute to exercise-induced gastrointestinal distress, including:
- Large or high-fat/fiber meals pre-workout: These take longer to digest and can still be sitting in the stomach when you start running.
- Overeating or underfueling: Too much food causes bloating, while too little can cause nausea.
- Unfamiliar sports products: Trying new gels or drinks during a race often leads to GI symptoms.
- Inconsistent hydration: Both dehydration and overhydration can cause problems.
- Excessive caffeine intake: Especially in concentrated forms, caffeine can be a gut irritant.
- Poorly timed meals or snacks: Eating too close to a workout may not allow enough time for digestion.
- Medications or supplements: Iron, magnesium, or NSAIDs can irritate the gut.
Identifying your personal triggers can help you make informed choices and avoid preventable issues. Keep a training and nutrition journal to spot patterns in symptoms and make data-driven adjustments.
How Gut Training Can Help Prevent Runner’s Stomach
One of the most effective strategies to reduce runner’s stomach is gut training.
Gut training is the process of teaching your digestive system to tolerate food and fluids during exercise. Just like your muscles adapt to training, your gut can adapt too.
The goal is to increase the stomach’s tolerance for volume and the small intestine’s ability to absorb carbohydrates.
Without gut training, even the best fueling plan can fall apart on race day. If your body isn’t used to digesting during high-intensity efforts, GI distress is almost inevitable.
Gut Training Tips:
- Practice your race-day fueling strategy during long training sessions. Don’t wait until race day to test your nutrition.
- Start with small amounts of fuel and gradually increase. This builds tolerance without overwhelming the gut.
- Use the same timing and types of fuel you plan to use in a race. Mimic race conditions as closely as possible.
- Track what works and what doesn’t in a training log. Note symptoms, timing, and product types.
- Stay consistent; gut training takes time. Most athletes need 6-8 weeks to see full benefits.
By incorporating gut training into your regular routine, you’ll minimize surprises on race day and better support exercise and digestion.
Tips to Manage GI Distress Before and During Exercise
Preventing GI distress during endurance exercise is all about preparation and personalization.
Here are several practical strategies you can start using today:
Before Exercise:
- Eat your last large meal 3-4 hours before training or racing. Stick to low-fiber, low-fat, high-carb options.
- Limit high-fat and high-fiber foods the night before and the morning of a long session. These slow digestion and increase the risk of gut issues.
- Drink plenty of water and electrolytes in the 24 hours leading up to your workout. Especially important in warmer climates.
- Avoid trying new foods or supplements right before a race. Stick to tried-and-true choices.
During Exercise:
- Use sports drinks or gels you’ve tested in training. Your gut needs familiarity to function well under stress.
- Don’t overload the stomach; space out fueling every 30-45 minutes. This avoids spikes in GI discomfort.
- Use a combination of water and electrolytes, especially in hot or humid conditions. Avoid plain water-only strategies on long sessions.
- Stay calm and trust your plan. Anxiety and overcorrection often make symptoms worse.
The key here is consistency. Athletes who stick to a dialed-in nutrition plan typically experience fewer and less severe GI symptoms.
When to Seek Help for Persistent Runner’s Stomach
While occasional stomach issues are common, frequent or severe symptoms aren’t something you should just “push through.”
If you’re dealing with ongoing GI distress, it could signal a deeper issue like:
- Food intolerances (e.g., lactose, gluten)
- Micronutrient deficiencies
- Dehydration or overhydration habits
- Inadequate carbohydrate intake
- Hormonal imbalances or RED-S (Relative Energy Deficiency in Sport)
- Poor gut-brain axis regulation
This is where working with a sports dietitian can make a huge difference. You don’t need to figure it all out on your own. A personalized plan can help you prevent exercise-induced gastrointestinal distress and build more confidence in your training.
When we work together 1:1, we can explore your dietary history, training load, stress levels, and supplement use to build a plan that not only improves performance but supports long-term health.
Ready to say goodbye to runner’s stomach and hello to GI distress-free races? Apply for 1:1 coaching here!
You Don’t Have to Suffer Through GI Distress
GI issues can be frustrating, embarrassing, and even race-ending. But with a deeper understanding of runner’s stomach, consistent gut training, and personalized nutrition strategies, you can reduce your risk and feel stronger on the course.
Every athlete is different, and what works for one person might not work for another. The key is to test, track, and tailor your fueling strategy to your unique needs.
If you’re tired of guessing and want support in managing your nutrition for endurance training, I’m here to help. Apply for 1:1 coaching or join the Flight Collective for community and expert guidance.
Your gut is trainable. Let’s get to work.
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