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No Gut Trouble on Race Day, More Glory

Gazelle Nutrition Lab / Blog  / No Gut Trouble on Race Day, More Glory

No Gut Trouble on Race Day, More Glory

Tackling Gut Issues in Athletes

Runner in the Mountains


Stomach trouble during exercise got you down? You aren’t alone. Athlete gut trouble is common. Studies suggest that on average, between 30 to 50% of all athletes experience some form of gastrointestinal (GI) distress. Gender, age, environmental conditions, and sport-type all factor into how often gut troubles turn up. In long-distance runners, for example, 30-90% report stomach issues, while in ultra-endurance events, 93% of long-distance triathletes demonstrate symptoms. Symptoms include nausea, vomiting, abdominal cramping, and diarrhea, and even blood loss in bowel movements.

Gut issues are more common in novice athletes but even the pros can’t avoid them. Des Linden, the 2018 Boston Marathon Champion, reportedly said of this year’s Boston finish “Honestly, I was just trying not to vomit”. Even soccer superstar Lionel Messi was plagued with vomiting before his matches before he reportedly changed his diet to include a healthier balance of foods.

In this blog, I look at why athletes suffer from gut issues and some possible solutions to your gut ailments.


Athlete Gut Trouble: Possible Causes

Reasons for athlete gut trouble is not fully understood. Even so, a look at gut biology can give us some clues about causes.

Exercise affects how your gut works. It changes its absorption and motility, as well as gut barrier function. But, it is not one size fits all.  There are might big differences in how your GI system reacts to exercise compared with your training buddy. What works for one person will not necessarily work for the next person.

Changes in Circulation

You need good blood circulation in your gut, or splanchnic perfusion, to optimally absorb nutrients.  During exercise, your body sends more blood to tissues that need it most- like your muscles, skin, heart and lungs- and less to your GI system. For some people, the effects are mild. For others, gut blood circulation is greatly reduced when they are exercising, especially during intense exercise. Such blood perfusion changes are linked to symptoms like nausea, vomiting, abdominal pain, and diarrhea.

Changes in Movement

Gut movement, or motility, also plays a role in GI symptoms during exercise. Soon after swallowing, the movement of our esophagus carries food to our stomach. Changes in how our esophagus moves, or in the muscle tone where it meets our stomach, can occur because of exercise. These changes may result in belching, reflux, nausea, and vomiting.

Lower down, physical activity can affect how readily food and fluids empty from our stomach into our GI tract for digestion and absorption. Studies suggest that both intense exercise and hypohydration (i.e. not drinking enough) affect our stomach emptying and can contribute to gut symptoms.

Changes in Permeability

Finally, there is a growing body of research about how intense and prolonged exercise may make our GI tract more permeable. Some researchers have found that the gut may become more permeable after running a marathon, and others have suggested that gut permeability may cause symptoms in runners.


Six Nutrition Tips to Try


Well-tolerated food and fluids are those that either minimize the effects of exercise on the gut or work in spite of the gut changes. Let’s have a look at the causes, and some tricks and tips that may help avoid that dreaded competition day on the toilet or in the bushes.


#1 Quench Your Thirst

Top 3 Hydration Tips


Start your exercise well hydrated. Dehydration exacerbates GI symptoms. A 2008 study from Creighton University in Nebraska, USA, found that water restriction during prolonged exercise worsens gut permeability.

What does this mean for your gut tolerance? It means poorer absorption and more chance of discomfort.

How can you avoid this fate? Drink 1-2 cups of fluid 2-4 hours before starting exercise, more if it is hot or you have not been keeping up with your hydration. Within the hour before exertion take in another ½ to 1 cup of fluid. Once you start the activity, drink small amounts often. For most athletes, amounts in the range of 400 ml to 800 ml per hour work well (or ~ 2 to 3 cups).

But, listen to your body cues and drink to thirst to avoid over-hydrating. Also, consider homemade or commercial sports drinks in hot and humid conditions or prolonged exercise to promote optimal fluid absorption and encourage frequent drinking. The gut absorbs carbohydrate-electrolyte solutions (i.e. sports drinks) more rapidly than water.



  • Hydrate well before, during, and after exercise. Dehydration worsens GI symptoms.
  • Pre-exercise- Drink 12-20 oz. of fluid with 8 oz. immediately before the event.
  • During exercise- 6-12 oz. of fluid every 15-20 minutes. Space your fluids rather than drinking them all at once to promote absorption.
  • Post-exercise- 16-24 oz. for every pound lost during exercise.


#2 Eat Food that Travels

Rice in a Bowl


Avoid foods that delay gastric emptying. The culprits? High fibre, high fat, high protein foods are digested more slowly than low fibre, carbohydrate-rich alternatives. Before and during a competition, you want food that is readily digested and absorbed for immediate fueling.

Before intense training sessions or competition day limit the following types of foods:


  • High Fiber

Regularly eating high fibre foods is suitable for general health, beneficial for blood sugar control, and promotes regularity. But, before intense exercise or competition, fibre can worsen GI issues.

Before a competition, avoid high fibre foods like brown bread or cereals, whole grains and vegetables. Include high fibre foods after training sessions, before less intense training sessions, and during rest days.


  • High Fructose Drinks

Soda as a High Fructose Drink

Avoid high-fructose drinks, like soda, before training. Interestingly though, a combination of glucose and fructose may be well tolerated during training. Examples of glucose/ fructose combos used by many long-distance cyclists and triathletes are bananas and sports drink, or a cola beverage and bread.


  • Concentrated Carbohydrate Solutions

Concentrated carbohydrate solutions (greater than 500 mOsm/L) and foods like soda and gels can create GI upset because they delay gastric emptying. But, carbs are beneficial to performance, so what should you do?

If using concentrated carbohydrates, the trick is to take them with sufficient water or to choose drinks with lower carb concentrations (i.e. most sports drinks). This approach prevents high concentrations of carbohydrates in the stomach and GI tract and in turn, avoids a shift of fluid into the intestine resulting in GI symptoms.

Even if you are only able to take in enough water with the carbs to minimize, but not avoid gut upset, this may be enough. Sometimes mild GI symptoms do not negate performance benefits. In one 2012 study looking at marathoners and Ironman finishers, higher CHO intakes were associated with mild nausea and flatulence but also with faster finish times. A little athlete gut trouble, it turns out, is not a game-ender.


  • High Fat Foods and Large Servings of High Protein Foods

Similar to fibre, fat and protein delay the emptying of food from our stomachs into our small intestines. If food is sitting in our stomach, we are more likely to experience GI symptoms. So, avoid high-fat foods and large servings of protein before your competitive event. Schedule that burger and fries meal you’ve been craving for after the finish rather than pre-event.



  • Choose low fibre, low fat, moderate protein, carbohydrate-rich foods before exercise.
  • During exercise, drink water with highly concentrated carbohydrate gels and solutions.
  • Avoid using high fructose drinks alone. When using fructose for endurance, choose drinks that contain a combination of glucose and fructose, or maltodextrin and fructose.


#3 Train the Gut

Endurance Athlete with Food Supplies


Athletes who are not used to eating and drinking while exercising are twice as likely to develop symptoms as athletes who are accustomed to eating and drinking during exercise. There are several reasons for improved tolerance to food with experience.

One reason may be that our ability to absorb and use fuel during exercise improves with practice. A 2010 study separated 16 endurance-trained cyclists into two energy-matched groups- a low carb group and a high carb group. After 28 days, the top carb group was able to oxidize- or use for energy- the carbs they took in at a higher rate than the low carb group. This difference in oxidation rate was thought to be due to better absorption in the top carb group.

Another study found that although gastric emptying did not improve with fluid training- stomach discomfort did improve. In this 2008 study, the researchers checked stomach tolerance during five runs where they coached participants to drink every 10 minutes to match their sweat loss. Participants rated their stomach comfort as improved on the fifth run compared to the first run.



  • Don’t be discouraged if you have trouble tolerating food and fluid when you first start eating and drinking during exercise.
  • Start with small amounts and work up.
  • Your ability to absorb, use and tolerate food and liquid during exercise will improve with practice.
  • Even if you are experienced, practice new nutrition strategies many times during training to perfect your competition day strategy.


#4 Rely on Sugar Variety

In your digestive system, carbs are broken down into their component sugars (i.e. glucose, fructose, and galactose). They are then absorbed from the intestinal lumen (i.e. the inside of your gut), into epithelial cells (i.e. the cells that line your gut), and then into the bloodstream via shuttles, called transporters, specific for glucose and fructose.  The availability of these transporters limits how many carbohydrates we can absorb each hour. This sounds complicated, doesn’t it?

What you need to know is that your glucose transporters are maxed out at about 60 g an hour.  If you are taking in fructose as well as glucose you can then use the fructose transporters to amp up the total carb you can oxidize, or use for fuel, hourly. With a combination of sugars, your gut can maximally absorb about 70-90 g of carbohydrates an hour and sometimes a bit more in well-trained athletes.

How does this help with gut trouble? You get better gut tolerance because you can absorb all the sugar rather than having it hang out in your gut, and causing fluid to accumulate there. In fact, beverages containing multiple transportable carbohydrates (like glucose and fructose) have been shown to reduce GI symptoms . This is similar to the finding in mountain bikers where multiple transportable carbohydrates (in this case maltodextrin and fructose) not only lead to enhanced performance but were better tolerated compared to using one sugar alone.



  • For exercise lasting longer than 2.5 hours consider taking in carbohydrate in amounts of 70-90 g an hour (or more in some people). To optimally absorb this quantity of carbs and to limit adverse GI symptoms, choose high carbohydrate foods, supplements, and fluids that provide a source of multiple types of sugars. For example, glucose and fructose, or maltodextrin and fructose.


#5 Eat Well in Advance of Exercise

Sunrise Exercise


Side stitches are more common in those who eat within 2-3 hours of exercise. Smart athletes schedule their meals well in advance of exertion. This suggestion is both the simplest and hardest one for many people. While the directions are straightforward, it can be a challenge to implement in practice for those who exercise early in the day.

While many will not be able to awake 2-3 hours before exercise, eating a full meal 15-30 minutes before you step out for a run is likely not a good idea either. Consider waking at least one hour before your exercise starts to give you time to eat and digest your food. If solid food doesn’t work for you first thing, consider a liquid meal like a smoothie. Also, take time to have a full bathroom break. Incomplete bowel movements are associated with urgency during activity.



  • Eat well in advance of exercise. If your exercise starts early, awake at least one hour beforehand to give yourself time to eat and have a full bathroom break.
  • Consider a liquid meal when pinched for time. Liquids are digested more quickly than solid foods.


#6 Probiotics and Nitric Oxide

Peppermint and Yogourt


Probiotics are good bacteria that are helpful for maintaining a healthy gut. As such, it stands to reason then that including probiotic-rich food in your diet may be helpful for athlete gut trouble. A small 2019 study in 24 recreational runners found that four weeks of probiotic supplementation leading up to a marathon significantly reduced GI symptoms in the last third of the race. Where can you get probiotics? Yogurt with live cultures and kefir are two sources, as well as supplements.

Nitric oxide (NO) is another potential strategy that may work by improving gut blood circulation. Researchers have looked at improving perfusion by looking at ways to increase NO production in the gut.

Options to do so include nitric oxide synthase-dependent (glutamine-arginine-citrulline) supplementation or nitric-oxide synthase independent (nitrate-nitrite) supplementation. This area of research is still in its infancy. And even if gut blood perfusion might be improved, vegetable sources of dietary nitrate are sometimes associated with GI symptoms.



  • Include probiotic-rich food in your diet daily. Give yogurt and kefir a try. For vegetarians, salty substitutes include miso soup or sauerkraut. Kombucha and supplements are also alternatives.
  • Include nitrate-rich food in your diet often. Beets and dark green leafy vegetables like arugula are sources of dietary nitrate. Be aware: sometimes these foods can worsen GI symptoms.


Other Solutions


Consider Impact and Posture

High impact sports may result in gut damage. Gut issues more common in runners than cyclists. Researchers theorize that the high impact of running causes intestinal damage and combines with the jostling of the stomach to result in flatulence, diarrhea, urgency, and even gut ischemia and bleeding in runners.

For cyclists, upper GI symptoms, like belching and reflux, may occur due to positioning. Swallowing air when taking in fluids from bottles or heavy breathing can further complicate the situation. For these athletes, training can help reduce this cause of GI distress.


Review Your Meds

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are a class of drugs that include medications such as ibuprofen and naproxen. Many athletes use NSAIDs for pain relief during sporting events. However, NSAIDs are associated with a three to five times higher risk for upper GI complications, mucosal bleeding, and perforation compared with no drugs at all. As such, use these medications with caution and consider avoiding them altogether if you experience persistent or recurring GI symptoms. Your best practice is to speak with your doctor or pharmacist for advice.


Get Zen

Meditating for Stress Relief

Stress has long been pinpointed as a potential culprit of gut issues. A 2018 study in 74 men and 76 women runners looked at GI distress triggers. Researchers found that anxiety and stress were correlated with GI symptoms even after other potential associations, like running experience and food and fluid, were considered. If stress is a significant part of your life it’s time to consider taking steps to make things a bit more zen. Aside from meditation and simplifying your daily activities where possible, you can also get some help from a mental health expert when needed.


Putting the Strategies into Practice

Gut symptoms during exercise can derail training and competition. Often, using the strategies I outlined can help or eliminate GI troubles. Sometimes, GI issues persist and require help from a dietitian and doctor. Some athletes may benefit from following a low FODMAP diet and reintroduction phase to pinpoint triggers.  This diet is outlined well elsewhere.

For most of us, we can get relief by changing what, and when we eat, around exercise. Trial the above strategies to see if any of them work for you. If your gut issues persist, consider seeking the help of a dietitian who specializes in the gut.


Nutrition planning is integral to achieve your optimal athletic performance. Gazelle Nutrition Lab delivers one-on-one or group nutrition counselling and consulting to both recreational and high-performance athletes. In addition, the Gazelle Blog is a free resource for healthy recipes and health tips. Have questions? We’d love to hear from you! Get in touch!


Additional Sources

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De Oliveira EP, Burini RC. The impact of physical exercise on the gastrointestinal tract. Curr Opin Clin Nutr Metab Care. 2009;12:533–538.

De Oliveira et al., Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med. 2014(Suppl 1):79-85.

Jentjens RL, Underwood K, Achten J, et al. Exogenous carbohydrate oxidation rates are elevated after combined ingestion of glucose and fructose during exercise in the heat. J Appl Physiol. 2006;100:807–816.

Lambert GP et al. Absorption from different intestinal segments during exercise. J Appl Physiol. 1997;83:204-212.

Lambert GP, Lang J, Bull A, et al. Fluid restriction during running increases GI permeability. Int J Sports Med. 2008; 29: 194–8.

Moses FM. The effect of exercise on the gastrointestinal tract. Sports Med. 1990;9:159–172.

Peters HP, Wiersma JW, Koerselman J, et al. The effect of a sports drink on gastroesophageal reflux during a run-bike-run test. Int J Sports Med. 2000;21:65–70.

Pfeiffer B, Stellingwerff T, Hodgson AB, et al. Nutritional intake and gastrointestinal problems during competitive endurance events. Med Sci Sports Exerc. 2012;44:344–351.

Rao KA et al. Objective evaluation of small bowel and colonic transit time using pH telemetry in athletes with gastrointestinal symptoms. Br J Sports Med 2004;38:482-487.

Ryan AJ et al. Effect of hypohydration on gastric emptying and intestinal absorption during exercise. J Appl Physiol. 1998;84:1581-1588.

ter Steege RW, Van der Palen J, Kolkman JJ. Prevalence of gastrointestinal complaints in runners competing in a long-distance run: an internet-based observational study in 1281 subjects. Scand J Gastroenterol. 2008;43:1477–1482.

van Nieuwenhoven MA, Brouns F, Kovacs EM. The effect of two sports drinks and water on GI complaints and performance during an 18‐km run. Int J Sports Med. 2005; 26: 281–5.




Ashley Leone

Ashley is a Sports Dietitian and Owner of Gazelle Nutrition Lab. Ashley provides nutrition advice and plans to athletes and everyday active people alike. Her goal is to help fuel your inner athlete and put good sense back into eating. Ashley is an enthusiastic and knowledgeable nutrition specialist, and has been a Registered Dietitian for almost 20 years.

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