Runners stomach, aka: “exercised-induced GI issues” are very common in endurance athletes, and not just runners.

It’s a horrible situation to be in, and unfortunately, most athletes have experienced exercise-induced GI distress a time or two. In fact, studies have shown that up to 50% of athletes have dealt with some form of GI issue during training and/or racing.

Before we dive into how the potential causes, it’s important to understand why runners stomach is a common issue for many people. Physiological changes, impact of exercise, posture, food, hydration, and supplements all can cause or worsen GI issues.

And every athlete is different in what’s triggering their issues. GI issues during exercise are highly individualized to the athlete. This is what makes it so challenging and frustrating.

And, this is exactly why when we work with our athletes we do a deep dive into several factors to determine the potential cause and work to eliminate or reduce the effect. 

Factors That Can Cause Runners Stomach

Changes in physiology while running.

Some symptoms may be a result of the physiological changes that happen when we run. Running can affect:

• Blood flows away from the gut and to the working muscles. This oftentimes will cause bloating or cramping. 
• Changes in the movement of food through the intestines. For some, there might be a decrease in gastric emptying leading to fullness and bloat. While others may experience an increase which can lead to diarrhea. 
• Change in circulating gut hormones. intense exercise like high-intensity intervals causes an immediate rise in your blood glucose and leads to an exaggerated release of hormones. These hormones include adrenaline and norepinephrine, which are released by the sympathetic nervous system (allowing your body to respond to physical or mental stressors with an increased heart rate). The effects of these glucose-raising hormones can affect gut motility. 
• Decrease in something called the LES (lower esophageal sphincter) tone—which can contribute to symptoms like acid reflux 
• How water and electrolytes move between the gut and the working muscles. While dehydration doesn’t necessarily cause GI symptoms, it certainly can make a small issue much worse. 

Food and improper timing around fueling 

Some foods, particularly when eaten too close to the start of exercise, can increase the likelihood of experiencing GI symptoms. Namely, foods that are high in: 

• Fiber
• Fat
• Protein and/or 
• Sugar substitutes or alcohols 

These can contribute to GI issues on the run because they take longer to digest.

Here are some ideas for what do to before a workout:

• Easy-to-digest carbs. Like applesauce. Toast with/ PB or jam. Yogurt. Choc milk. Lower-fiber cereal.
• If you have a finicky stomach, liquid calories get digested quicker than solid foods.
• Give 3-4 hours for a full meal to digest before starting a workout. And 1-2 hours for a snack. Especially for runners as a full tummy while running can cause GI issues.
• Hydrate!!! Dehydration can also lead to GI issues no matter how perfect you are. Especially in these hot summer days.

Another common issue is poor nutrition intake or timing during the run. For some athletes, consuming too many carbohydrates at once rather than spacing it out over time can create issues. For others, it often is because not enough fluids were taken in alongside fuel. 

Lastly, it takes practice and time to allow your gut to adapt to taking in fuel while exercising. Be patient and diligent in building your gut’s tolerance. It is actually well established in research that for those who are not used to taking in food and fluid during exercise are twice as likely to develop GI symptoms. 

Supplements

Some supplements may also trigger digestive issues for athletes. Caffeine, while yes—can absolutely act as a performance aid, can also increase gut motility and is associated with nausea during exercise so trial it well in training to know it’s not going to lead to issues on race day.

Iron or magnesium, while hugely beneficial to those athletes who are deficient, do have reported GI side effects, so the timing of those supplements can be crucial.

Easy Ways to Help Prevent Runners Stomach:

• Drink extra water to prevent dehydration. Use electrolyte + hydration mixes as needed.
• For every 100 calories of nutritional product, you consume, aim to take in 4-8 oz of water to help digest and break down the product
• Be cautious with caffeine. Caffeine is known for having a laxative effect, especially coffee. 
• Avoid high-fiber foods for a few days before your competition. Fiber increases fecal bulk and movement. Eating a fiber-rich diet during training is great to keep your bowel movements regular, but for competition day you will want to decrease your need to travel to the bathroom. Some especially high-fiber foods to pay attention to are: veggies, seeds, whole grains like oats or quinoa, or nutritional products that have added fiber
• Motion is lotion, so on the evening prior to the event, I go for an easy-effort run for 20-30 minutes. I’ve affectionately dubbed this as my “colon-cleanse run” and it works every time to take care of the bowel business and have less worry about it during the race.
• Limit foods that contain sugar alcohols such as sorbitol, mannitol, xylitol, etc. Sugar alcohols don’t fully digest and can ferment (a.k.a. – cause gas) in the gut.
• If you have an inkling that you may have a sensitivity to gluten or Celiac disease, consult your doctor for testing. Most people with these diagnoses will see a rapid response, showing improvement within weeks when eliminating gluten from their diet.
• As there are many factors that can contribute to GI problems, it’s important to try different eating and drinking patterns and types of foods. Creating a list of “safe” foods to eat and a pre-competition ritual will provide you with the confidence to know you won’t lose your race due to an unexpected trip to the porta-toilet.
• For a lot of athletes, bowel issues may resolve themselves as training progresses so this hopefully will be the case for you.
• You may want to consult a doctor. There could be a potential bowel disease or problem that requires medical action.

The Takeaway

As I’ve mentioned, this issue is SUPER common in endurance athletes. So you are not alone.

If things are really bad. Consult a doctor, make sure there isn’t a medical issue, and then consult a dietitian, we’ve got ways to help you work through this.

My number one priority for my clients is to enjoy their race without worrying about porta emergencies and feeling their very best. 

My team and I are here to support you. We are an experienced and passionate team and can help investigate your GI issues and how to get you training and racing confidently. Our 1:1 program is ideal for fine tuning your fueling and nutrition.