4 Tips to Prevent & Manage Runner’s Stomach

Gut Training for Long Distance Runners: How to Avoid GI Distress and Improve Your Race Times

Runner’s diarrhea. The trots. GI distress. 

No matter how you slice it, having the sudden urge to hit the toilet mid-race is never fun — but it is unfortunately common. If you ask a random sampling of runners, a majority will likely say that they have experienced gastrointestinal distress during long runs or long distance races.

According to an article in Human Kinetics, almost 90% of endurance runners have reported GI distress during a race. Perhaps you have been one of those runners – but that doesn’t mean you are doomed to have runner’s trot ruin each shot at a PR.

In fact, learning how to prevent runner’s diarrhea can actually help you avoid distress and have a better race experience – with likely a faster finish time as well.

How Gut Training Can Improve Your Race & Avoid Runner’s Diarrhea

Many racers associate fueling mid-run with runner’s diarrhea – and therefore avoid it overall. However, skipping mid-race nutrition will lead to poor outcomes in the half marathon, marathon, and ultra distances. Intra-race carbohydrate intake enhances performance in long distance races. With the correct fueling strategy, you can run a marathon without hitting the wall.

The carbohydrate recommendations for marathons (and other races) are quite high. A 2022 review in Sports Medicine synthesized the large body of research on nutrition for running performance and suggests 60 grams of carbohydrates per hour for long-distance running races. For half marathons, the recommendation is 30-60 grams of carb per hour; for marathons and ultras, the recommendation is 60-90 grams of carbs per hour.

That is a lot of carbohydrates! If you consume 60 grams of carbohydrates on race day without having trained your gut to tolerate it, your chances are high that you will experience the runner’s trots – especially when you factor in race day nerves. However, the gut is a muscle – it can be trained to tolerate a lot of nutrition even during higher intensity running. Gut training throughout your training cycle will prepare you to handle all those carbohydrates on race day, without stomach upset.

A 2017 study in Applied Physiology, Nutrition, and Metabolism concluded that by taking carbohydrates on training runs (one group from gels, the other from whole food), runners were able to reduce the symptoms of GI distress and improve their performance in a one-hour distance test. However, the placebo group did not see a reduction in symptoms or an improvement in performance. Practicing your nutrition strategy in training will reduce your risk of experiencing runner’s diarrhea – and help improve your marathon time.

4 Tips to Avoid Runner’s Stomach on Race Day

1. Take Note of Food Sensitivities

Even if you don’t suffer from full-blown food allergies, most people have a few foods that don’t sit quite well with them. Foods such as dairy (lactose), high-fiber foods, and greasy foods can cause stomach irritation. While you may feel fine eating these foods on a normal basis, you may find you feel your best forgoing them in the 12-24 hours before a long run.

If you pay attention to what you eat and how you feel afterward, you can get a sense of foods that you may want to avoid before a long run. Common culprits can include cruciferous vegetables, dairy, legumes, and soy products – but some runners find that eggs, red meat, or any fibrous vegetables cause GI distress. Ultimately, it takes trial and error and close attention to your diet, but once you know your food sensitivities, you can adjust accordingly for better long runs.

2. Practice Your Fueling in Training

Repeatedly practicing your fueling during training is the best way to minimize the likelihood of runner’s diarrhea on race day. You can actually train your gut to absorb more carbohydrates during exercise, so fueling in training will improve your body’s ability to digest carbs.

You want to begin gut-training early on in a training cycle – don’t wait until the taper to try out gels. Gut training can take trial and error. You may need to experiment with different products along the way, requiring several weeks to find the products that sit best for you.

These steps can help you train your gut to tolerate your fueling:

  1. When first trying a new gel or other fuel, start on an easy run of 60-90 minutes in duration.
  2. Start fueling on all long runs >90 minutes in duration. The recommendations are 30-60 grams of carbs per hour for runs less than 2-2.5 hours; start on the lower end (such as a gel every 40-45 minutes).
  3. Gradually increase the frequency of your gels on long runs, until you can tolerate a gel every 20-30 minutes (depending on carbohydrate goals).
  4. In the 6-8 weeks prior to your race, start taking gels during race-pace workouts. These can include long run workouts or shorter mid-week workouts at race pace. You want to train your gut to tolerate your fuel at a higher intensity.
  5. Since gut cells turn over quickly, take a gel in your final long run during the taper and your race-week workout.

3. Hydrate Adequately

Oftentimes, it’s not the gels that cause runner’s diarrhea – it’s your lack of fluid intake. Dehydration delays gastric emptying rates due to reduced blood flow to the gut. The slower your gastric emptying, the longer those gels are sitting on your gut and possibly causing GI upset. However, too much fluid intake can also cause stomach upset.

Drinking to thirst is sufficient for runs lasting 1-2 hours (depending on the runner). Once runs exceed two hours, you want a fluid strategy to ensure optimal hydration for both performance and gut comfort. Depending on your sweat rate, you need 10-24 ounces per hour (replacing approximately 50-75% of your sweat loss). (This calculator from Featherstone Nutrition guides you through how to calculate your sweat rate and fluid needs.)

In addition to adequate fluid intake, you want to replace electrolytes during runs. Electrolytes including sodium play an important role in fluid absorption and retention. Similar to fluids, too little or too much sodium can cause runner’s trots. The heavier you sweat, the more sodium you need. While there is individual variation, generally, light sweaters need 200-400 mg of sodium per hour; moderate sweaters need 400-600 mg of sodium; and heavy sweaters need 600-1000 mg of sodium.

Related: Salt Tablets for Runners

4. Be Willing to Experiment

GU and Gatorade may be the bread and butter of your average aid station but that doesn’t mean they need to be your choice for fueling and hydrating.

Your options are numerous even in terms of sports nutrition products. Options for runners prone to runner’s diarrhea or who can’t tolerate the saccharine taste of GU and Gatorade include gels such as Huma, Honey Stinger, and Hammer, drink mixes such as Tailwind or Generation UCan, or chews such as Glukos Energy Gummies.

Some runners prefer sports nutrition products for their ease of use – they are designed to deliver the exact amount of carbohydrates in an easy-to-consume form. Do know that some gels and drink mixes contain caffeine, which can irritate the stomach and increase the urge to go – you must read the labels! For some runners, the concentration of carbs and sugars in gels or chews can cause GI distress – which is when you want to look at alternative options. 

You are not confined to the products offered on the shelves of the sports nutrition aisle. While most runners opt for the convenience of a gel, you can choose your fuel from your pantry. Pretzels, gummy candy, applesauce, homemade banana chips, and dried fruit are all carbohydrate-rich and portable foods that you can eat on the run (literally). Just know that if you take natural fuel, you will need to be mindful of getting enough electrolytes (see above).

Patience is key. You will likely sample a few products that do not agreement with your stomach, that taste bad, or that don’t seem to have any effect on you. If you are training for a marathon or half marathon, don’t wait until the peak weeks of training to experiment – start early on in training or even in the base building period before.

5. Avoid NSAID Use (Unless Necessary)

A Coach Can Help Prevent Runner’s Diarrhea

A knowledgeable running coach will have knowledge of the array of products on the market, the general guidelines of nutrition, and the most recent research. The generic rule of “one gel every 45 minutes” does not work for all runners – just like cookie cutter training plans don’t work for all runners. A coach will work with you individually to develop, test, and perfect fueling strategies for both training and racing.

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25 Responses

  1. My first few long distance races didn’t involve any mid race fuel. Sometimes I’d feel good, sometimes I’d bonk big time. Fueling for me is tricky. Once I seem to find what works, my body changes its mind. I’ve had great success with Huma Gels and most recently Tailwind. I love that stuff!

    1. They sent me some samples to try and I’m excited to try it for summer! I like Hammer, but drinkable fuel with electrolytes sounds so convenient for summer long runs.

  2. I had some issues with fueling on long runs a few years ago. I did lots of experimenting and found some fuel that worked for me. Now that i haven’t done long runs or taken fuel on a run in so long, Im going to be starting completely over when I get back to it!

  3. You know I am alllll about the gut training! I had my gut so well trained during my first two marathons. Not as much during the last two, but I was running much harder, and that tends to play a part in how… fast/slowly my gut works, lol. But no cramping, which is key! SUCK IT CROHNS

  4. I’m still trying to find the best thing that works for me, but I find that if I eat a gel slowly (consume little by little over a mile), it helps me avoid any GI issues. I also run with a handheld bottle filled with one Nuun tablet and water to make sure I am getting in enough electrolytes and staying hydrated.

    1. Eat the gels slowly makes so much difference by keeping gastric emptying working – plus it’s so hard for the body to digest all of that at once when running! Races out here have Nuun at the aid stations (they’re a West Coast company) and that makes such a difference in hydration!

  5. Gu is GROSS. It makes me gag. How it’s so popular I’ll never know. I’ve had good luck with Clif chews and Hammer gel. I’ll be using just the gel this time, because I don’t want to buy both. I love the Hammer raspberry flavor with real raspberries in it!

    1. Hammer is my favorite – just like you, I like how it has real fruit in it and the flavor is more mellow and the texture is more palatable than Gu. GU is too sticky and too sweet!

  6. I get GI issues whenever I do a really hard workout and especially when I race so I take Immodium beforehand. I definitely stay away from any veggies and even fruits. I’ve got a pretty cranky stomach! I don’t use a whole lot of gels and chews during races and none during training runs, not because my stomach can’t handle them but because I don’t find a difference between when I use them and when I don’t! I’m not normal though–so don’t use me as an example of what to do.

    1. Hard running puts a pounding on the gut! I never understand when people eat stuff like apples or greens smoothies before a run. How do their stomachs handle that?

  7. I stopped using gels quite a while ago — part of the reason being one you mentioned — I like to take in a little bit every mile than all at once. I tried the gel flasks, but eventually I just got away from it.

    I’ve been experimenting with real food for my runs/races for several months now — seems to be working, but it sin’t quite as convenient as a gel — but often tastes a lot better!

  8. When I did my first half marathon I don’t think I had even encountered the concept of eating during a run yet. My stomach felt super crampy afterwards, though I’m not sure whether it was the lack of fuel or electrolytes (I think I did have some gatorade). I’ve used Honey Stinger products before but I think I need to try Hammer gels – they’re what most of the races here have at aid stations.

  9. such great info! so I used to do jelly beans until I switched to hammer gels. I just sip them too and rarely finish one unless it’s a race. what’s interesting is that over the last several months or so, I have gotten away from opening one during routine long runs. I find that I can now get through long runs without them (as long as I’m not overly pushing my pace). my problem is that not taking in gel leaves me feeling as though I may need to retrain my stomach to accept it! ha! I never really had an issue though so I am hoping I wont for next week’s 10 mile race lol

    1. Thank you! I think you’ll be fine – even if they do cause problems, a 10 mile race will be over with quickly. But I don’t think you will have a problem because your body is trained for the Hammer gels.

  10. This is such a great post! As someone who has massive GI issues, I have really had to practice my fueling and do find that fueling mid-run with chews/electrolytes helps but it took me a while to figure out what kind of fuel my belly could handle.

    1. Thank you! Practice really does help in reducing GI issues – it teaches the body how to digest while running. I’m glad you found what worked for you!

  11. I’ve been thinking a lot about experimenting with different fueling options. I normally prefer using chews but I still need to make sure I have the right amount of electrolytes. I recently got the Saltstick in my Stridebox so I’m looking forward to testing it out this weekend!

    1. I saw that they had those new Saltstick chews! I hope they work out for you – finding the right balance of electrolytes takes trial and error also but will help so much once you do find the right product for you.

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