The 15 Best Ways to Prevent and Overcome GI Distress During an Ultramarathon

stomach issues

Studies have suggested that over 90% of ultra-runners experience at least one gastrointestinal-related symptom during the Western States ultramarathon (Stuempfle & Hoffman, 2015). You’d be hard-pressed to find an ultra-runner that hasn’t had some stomach problems in a race. GI issues remain the most common reason ultra-runners give for a DNF in ultramarathons.
In this blog, we will address strategies ultra-runners can use to minimize the chances of experiencing common symptoms of GI distress and ways to overcome such issues should they turn up during an ultramarathon.

Common Stomach Issues in Ultramarathons

During ultramarathons, common gastrointestinal (GI) problems include nausea, bloating, heartburn, diarrhea, and vomiting.

Why Are Stomach Issues So Common During Ultramarathons?ultramarathon stomach issues

Stomach issues frequently arise during endurance exercise because blood is diverted from the stomach to working muscles during activity, significantly hindering digestion. GI distress is especially prevalent in ultramarathons because ultra-runners need to eat a significant amount to prevent glycogen depletion (bonking).
High carbohydrate intake is necessary to prevent glycogen depletion and is associated with a higher rate of race completion. However, high carbohydrate intake can also result in GI distress.

How Ultra-runners Can Prevent Stomach Issues From Occurring During Ultramarathons

Prevention is always the best medicine, right? You should do everything in your power to PREVENT gut issues from arising in the first place. Then, if they do, know how to overcome them. For this reason, the top of my list focuses on prevention, while the bottom covers ways to overcome GI issues.

#1. Train Your Gut

Training your gut is probably the most crucial thing an ultra-runner can do before race day to avoid GI problems, hence the #1 spot. You should try to incorporate as many calories in training as you plan to consume on race day. For example, suppose your goal is to take in 300 kcal/hr during your ultramarathon. In that case, you better be doing some long runs incorporating 300 kcal/hr.

Additionally, you need to train your gut for the specific types of foods, gels, drinks, or whatever you intend to consume on race day. Training the gut is critical for avoiding nutrition-related disasters on race day. Additionally, doing so can increase the amount your stomach can handle, allowing you to better fuel your performance.

#2. Nothing New On Race Day

If you’ve never eaten a double-cheeseburger (not recommended) during a training session, then it’s not a good idea to eat one during an ultramarathon. Experiment with a variety of different fuels in training and find out what works for you. 50 miles into a 100-mile ultramarathon is not the place to try something new. Remember, just because your stomach does well with a particular food when sitting at the kitchen table doesn’t mean it will react the same when you’re running.

#3. Eat Breakfast 2-3 Hours Before Exercise

It’s important to eat breakfast before an ultramarathon to prevent stomach issues. Going in fasted will increase the likelihood of nausea. It’s also essential to eat the right foods for breakfast and at the appropriate time. Protein and fat can take over twice as long to digest compared to easy-to-digest carbohydrates. Additionally, eating too close to the race start, and you won’t have given yourself enough time for digestion, which can also lead to GI issues.

Lastly, remember to go with a tried and true breakfast you’ve used before multiple training runs. Check out this blog, Pre-Workout Nutrition For Ultra-Runners, for more information on how to dial in the hours leading up to a race or workout.

#4. Have a Plan

Know what you are going to use as energy and how much of it you will use. Yes, you will almost certainly have to adapt, and sometimes a plan can go out the window.  That’s just part of ultra-running.  However, that’s no excuse for not having a plan.  Determine how many kcal/hr you plan to consume and where those calories are coming from. Additionally, create a backup plan should you run into issues like palate fatigue or GI issues.

#5. Stick to Simple Carbs and Easy to Digest Sources of Fuel

Simple carbs are king in endurance sports, and ultramarathons are no exception. Things like carbohydrate drinks, gels, chews, and other simple sugars form the foundation of most of the energy ultra-runners take in.  The simpler the food, the easier it is to digest. Multiple transportable carbohydrate solutions contain various forms of sugars and have shown superiority to isolated sugars.
Remember, the majority of health consequences associated with simple sugars don’t apply during endurance exercise.

#6.  Stay Hydrated, Maintain Electrolyte Balance, and Stay as Cool as Possible in the Heat

Ok, so this technically could have been three different things, but they often go hand in hand with one another. Too little water, insufficient electrolyte intake, and overheating can all cause your stomach to sabotage you on race day.  

  • Know how much liquid and electrolytes you need to take in based on the heat index and your individual sweat rate (have a plan).  
  • Cool off at aid stations with cold towels, misters, throw some ice in a buff or arm sleeves, and drink something cold.

#7. Avoid NSAIDs

NSAIDs (like Ibuprofen) should never be taken during an ultramarathon. Yes, I know you have seen it (or done it) countless times. That doesn’t make it wise. The science is clear – NSAIDs are dangerous during endurance activity. They don’t improve your performance, and they can wreak havoc on your stomach. Please, take the time to read Why Endurance Athletes Shouldn’t Take NSAIDs.

#8. Improve Gut Bacteria with Probiotics

A healthy gut microbiome decreases an ultra-runners tendency towards GI distress. Specific strains of probiotics that have been shown to provide benefits including Lactobacillus and Bifidobacterium species. A 2019 study showed that 4 weeks of supplementation with the previously mentioned strains lowered the incidence of GI symptoms in marathon runners (Pugh et al., 2019).  Additionally, limiting the consumption of saturated fat can also positively influence the gut microbiome.

Overcoming Stomach Issues During an Ultramarathon

If you find yourself with stomach issues during an ultramarathon, don’t panic. All is not lost, and there is are usually ways to overcome whatever symptoms you may be experiencing.  Let’s switch gears and talk about some of these strategies.

#9. Slow Down

I know, I know, nobody wants to slow down during a race.  But more often than not, a modest drop in pace will help resolve common gastrointestinal distress symptoms.
Lowering your intensity allows more blood to redirect to the stomach, aiding digestion.  Plus, we are talking about an ultramarathon here. A small sacrifice in pace isn’t going to break you, but blowing chunks and being curled up in the fetal position on the side of the trail might. There’s typically a lot of miles to make it up!

If, however, you find yourself with stomach problems in the last 10% of a race, this might be a time that grunting it out and pressing forward at a higher intensity is justifiable.

#10.  Switch to Liquid Fuel

Switching to 100% liquid sources of fuel can be beneficial for ultra-runners experiencing GI distress. Liquids are easily digested and easier to get down when your stomach isn’t feeling up to par.
The best liquid fuel sources are “multiple transportable carbohydrate solutions.” Such solutions contain multiple forms of carbohydrates (glucose, fructose, maltodextrin, etc.), increasing absorption and decreasing the odds of gut discomfort compared to single carbohydrate solutions.

#11.  Keep Drinking

Hopefully, you remember that staying hydrated during ultramarathons was one of the keys (#5) to preventing stomach issues in the first place. Additionally, when problems creep up, it is critical to keep hydrating (water and electrolytes).  Sometimes, when a runner’s stomach is churning, the instinct is to not take in ANYTHING. This is understandable; consuming liquid doesn’t even sound good in extreme cases of GI distress. However, you must continue to hydrate; otherwise, you are in for more serious issues. 

Suppose you absolutely cannot keep anything down. In that case, it’s time to slow the pace significantly and even stop and rest if necessary until you can.

#12.  Reduce Intake in Increments

When the symptoms of nausea and/or bloating come on during an ultramarathon, it’s probably time to slow down (#6) and decrease your calorie intake in increments. There is no exact number of calories you should cut, as this depends on your body and the situation. Heat, how much you’re slowing pace, and what’s causing the symptoms in the first place are all factors to consider.
A good place to start might be to drop by 100 calories in the first hour and see if that provides relief. If not, an additional 50 might be warranted in the next hour and another in the next. So I might look something like this:

Planned kcal/hr – 350 kcal/hr

1st hour after symptoms – 250 kcal
2nd hour – 200 kcal
3rd hour – 150 kcal

I can’t recommend dropping below 150 kcal/hr, and staying below 200 kcal/hr for extended durations is also not recommended (see #12). When symptoms diminish, increasing intake in increments in a similar fashion is recommended.

#13.  Be Persistent With Intake

Not only should an ultra-runner be persistent with hydration, but they should also be persistent in acquiring at least SOME energy.  In longer ultramarathons, a consistent intake of less than 200 kcal/hour is not recommended.  Some degree of tenacity and stubbornness is eventually warranted when it comes to choking down some fuel. Although it’s not particularly pleasant and seems counterintuitive, failure to do so will likely make matters worse.

#14.  Replace Some Carbohydrates With Fat

Converting fat to energy isn’t as efficient as converting carbohydrates to energy. However, replacing some carbs with fat may positively affect your stomach during times of GI distress. After all, taking in some fat in place of carbohydrates is far better than not taking in anything at all. Try things like white tortillas filled with avocado or nut butter.  Remember to try these foods in training sessions before incorporating them into an ultramarathon.

#15.  Ginger

Ginger is a fantastic herb when it comes to helping alleviate nausea. If you are an ultra-runner, you have likely seen ginger at ultramarathon aid stations in the past. Keeping some form of ginger in drop-bags and with your crew is a good idea. Evidence suggests 1500 mg of ginger is effective for nausea relief (Nikkhah Bodagh et al., 2019).





Summary – Preventing and Overcoming Stomach Issues During an Ultramarathon

Nausea, bloating, indigestion, and other common gastrointestinal problems wreak havoc on endurance athletes and optimal performance. This is especially true in ultramarathons. However, you can significantly reduce the odds that stomach issues will ruin your big day with a little planning and practice.




Disclaimer – Use common sense, and always listen to your doctor over a blog post. They know more about your personal health situation than anybody behind a keyboard. As someone who has a Graduate degree in Clinical Nutrition, I realize the variance that certain medical conditions create when it comes to optimal nutrition and supplementation. If you have underlying medical conditions, always check with your doctor before starting a new supplementation routine.



Nikkhah Bodagh, M., Maleki, I., & Hekmatdoost, A. (2019). Ginger in gastrointestinal disorders: A systematic review of clinical trials. Food Science & Nutrition, 7(1), 96–108.

Pugh, J. N., Sparks, A. S., Doran, D. A., Fleming, S. C., Langan-Evans, C., Kirk, B., Fearn, R., Morton, J. P., & Close, G. L. (2019). Four weeks of probiotic supplementation reduces GI symptoms during a marathon race. European Journal of Applied Physiology, 119(7), 1491–1501.

Stuempfle, K. J., & Hoffman, M. D. (2015). Gastrointestinal distress is common during a 161-km ultramarathon. Journal of Sports Sciences, 33(17), 1814–1821.






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