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

Gut Training for Long Distance Runners

If you ask a random sampling of runners, a majority will likely say that they have experienced GI distress during long runs or long distance races. According to a recent article in Human Kinetics, almost 90% of endurance runners have reported GI distress during a race. Perhaps you have been one of those runners – I have – but that doesn’t mean you are doomed to suffer GI distress every time you take in some fuel during a marathon or half marathon. In fact, gut training can actually help you avoid GI distress and have a better race experience – with likely a faster finish time as well.

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

How Gut Training Can Improve Your Running

Many runners associate fueling mid-run with GI distress and therefore avoid it overall. However, not fueling at all during a marathon or longer event can have disastrous consequences, many of which could land you in the medical tent. Running for over two hours without any fuel can lead to bonking, lightheadedness, confusion, fatigue, and low blood sugar – not exactly what you want when you are aiming for a half marathon or marathon PR.

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. Quite simply put, gut-training will not only reduce the risk of GI distress on race day – it will help you run a faster marathon or half marathon.

Both scientific research and anecdotal experience support the efficacy of fueling during a long run or long distance race. Your body uses a combination of carbohydrates and fat to produce energy on a run. When you deplete the stored carbohydrates (usually after 90 minutes to 2 hours worth of running, depending on the intensity), you will bonk and slow down unless you take in more calories and carbs. Consuming 30-60 grams of carbohydrate per hour during long distance running events will help you avoid the dreaded wall and stay on your goal pace throughout those grueling final miles.   

You would not wait until race day to practice training at goal race pace or running long distance – and likewise, you should not wait until race day to try out your fueling strategy. You are far more likely to experience GI distress with the combination of the physical stress of racing, new products, and race day nerves. Training your body to handle fuel is another piece of the marathon and half marathon training puzzle – just like strength training and goal pace training.

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. For me, it’s high-lactose/unfermented dairy, beans, and cruciferous vegetables – and I deliberately avoid those foods in the 24 hours before long runs if possible.

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.

Practice Your Fueling in Training

Repeatedly practicing your fueling during training is the best way to minimize the likelihood of GI distress 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 – because it may require trial and error, which is not what you want to deal with during the peak weeks of marathon training. Begin with a smaller volume of fuel on a shorter long run (~90 minutes), especially as you sample different products. From there,  gradually increase the frequency of your fuel until you feel strong and energetic throughout your long runs.

Gut Training for Long Distance Runners

How you take in fuel during a run makes a difference and therefore is also something to practice in training.  Unless the gel states otherwise, take water with them to improve gastric emptying. Some runners prefer the sipping method (or slowly eating a pack of chews or food) to reduce the volume hitting your stomach all at once, which in turn improves the rate of digestion and reduces GI distress.

Ideally, you want to rehearse your exact race day fueling strategy at least twice in training. This best occurs during 18-22 mile runs for the marathon and 12-14 mile runs for the half marathon. You also want to practice taking in your fuel at goal race pace if possible, since faster running burns more carbohydrates but can also lead to more stomach upset.

Don’t Forget Electrolytes

The culprit of GI distress on a run isn’t always related to fueling – it may be caused by dehydration and electrolyte imbalance. Dehydration and electrolyte imbalance can cause stomach cramping, nausea, and other GI issues – not to mention the risk of dangerous medical conditions such as hyponatremia (too little sodium in the bloodstream).

Water alone may prevent dehydration, but it won’t prevent cramping or fluid imbalance. Sodium, potassium, magnesium, and calcium are the most vital electrolytes for runners. Products such as Nuun, Enduropacks, Tailwind (which also provides carbs), or Salt Stick will all provide the electrolytes you need to stay hydrated and run cramp-free.

Whether you carry your own electrolyte supplements or drink from the race’s offering, you want to be diligent about consuming these minerals during the race. If you opt for traditional electrolyte drinks that contain carbs and sugars, factor those into your fueling plan so that you are not oversaturating your gut during the race. Practice your electrolytes in training to find what works best for you.

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 GI distress 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.

Gut Training for Long Distance Runners

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.

Work with a Coach

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.

Want to learn more about my coaching services? Email me at [email protected] or check out my coaching page here!

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Have you ever bonked or experienced GI distress in a race?
Do you prefer gels, chews, drinks, or whole foods as fuel?

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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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