Lifestyle | Health & Wellness

How to Avoid Gastrointestinal Issues During Exercise

Learn How to Avoid Gastrointestinal Issues During Exercise When You Have IBS

Did you know that over 50% of endurance athletes complain of gastrointestinal symptoms during an endurance event such as cycling, triathlon and running? Some of the most common symptoms reported include nausea, vomiting, bloating, abdominal pain, urgency to go to the toilet, diarrhea, and in some situations, involuntary projectile vomiting. This article is about learning How to Avoid Gastrointestinal Issues During Exercise.

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Diet Is a Start

Following a low FODMAP diet can definitely help, but there are also other things that can be done to help prevent GI issues during exercise.

When we start exercising, our body undergoes some natural changes to prepare itself for the actual exercise stress, which can perturbate (agitate) the gastrointestinal tract.

When we start exercising, two main things occur.

First, there is an increased stimulation of the sympathetic nervous system, which reduces gastric emptying and intestinal motility. This can impair the transport of nutrients, which means that if we consume carbohydrate or other nutrients during exercise, the uptake of those nutrients into the body and into circulation may be impaired, which leads to malabsorption. Carbohydrate and protein malabsorption can occur during exercise, but also after exercise with a post exercise recovery beverage.

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Simultaneously, when we start exercising, the blood flow moves into the muscles to provide muscles with oxygen and nutrients. Therefore, there is less oxygen available along the gastrointestinal tract, which creates damage and inflammation to the gut. This allows the bacterial content of the intestine to leach into normal circulation, which can lead to GI symptoms.

Those perturbations to the gut are called the exercise-induced gastrointestinal syndrome. Factors that can exacerbate exercise-induced gastrointestinal syndrome include exercise intensity, duration, and mode, the fitness status of the participants, their level of tolerance to foods and fluids during exercise, exercising in the heat and acclimation to the heat, as well as taking anti-inflammatory agents.

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Strategy for Success

Fortunately, there are things that you can do to help prevent GI issues during exercise.

Here are 3 nutrition tips to help prevent exercise-induced gastrointestinal syndrome.
1- Choose low FODMAP foods and drinks before and during exercise

Following a low FODMAP diet (which will include the reduction in dietary fiber) in the days leading up to competition and during periods of intensified training can help you reduce gastrointestinal symptoms during and post exercise, whether you have IBS or not. This means that it is preferable to avoid ALL high FODMAP foods, even those that you can usually tolerate. This is because during an intense or prolonged effort, your tolerance to fermentable carbohydrate can be diminished, causing malabsorption and GI symptoms. If you have a sensitive gut, you should also make sure to choose low FODMAP sports supplements. Choose sports drinks and gels with a 2:1 glucose to fructose ratio. This information is usually specified on the label.

2- Start your exercise well hydrated, and avoid both dehydration and over-hydration   throughout exercise

Dehydration can increase gastrointestinal issues during exercise. Firstly, it causes the plasma volume to decrease, which reduces blood flow to the gut and delays gastric emptying. Secondly, it reduces the ability of our body to regulate temperature, resulting in greater core temperature.

On the other hand, over drinking to the point of overwhelming the stomach can also lead to GI issues. Studies show that proper hydration before and during exercise can reduce the frequency of GI symptoms and reduce malabsorption of carbohydrates from the pre-exercise meal.

The American College of Sports Medicine recommends drinking 5 to 10 ml of fluid per kg of body weight two to four hours prior to exercise to optimize hydration status. A very pale colored urine (like lemonade) is a good indicator that you are well hydrated. However, keep in mind that taking multivitamins can affect the color of the urine. To estimate your fluid losses during exercise and know how much fluid you should drink during exercise, you can weigh yourself before and after your workout. You should aim for a weight loss of no more than 2% to 3% of body mass during your exercise bout. Finally, drinking cold drinks when exercising in the heat also can help reduce gastrointestinal symptoms.

3- Train your gut to tolerate carbohydrate during exercise

Consuming carbohydrates during prolonged exercise (2 hours or more) is recommended with aim to maintain blood sugar levels, provide energy, attenuate fatigue and enhance performance. However, if your gut is not used to absorbing and processing carbohydrates during exercise, this can cause malabsorption and lead to gastrointestinal symptoms.

It is important to train your gut to increase carbohydrate tolerance during exercise using a structured gut-training protocol at least two weeks before a competition. It is advised to use lower carbohydrate concentration beverages, and consider adequate water intake in adjunct with any solids being consumed, including semi-solid forms like sports gels, because hypertonic solutions (solutions that are too concentrated in nutrients) reduce gastric emptying rates or in other words slow down digestion and are more likely to cause GI discomfort.

The Takeaway

Basically, what this all means is that you should make sure to consume enough water when consuming gels or other foods, and choose drinks that contain no more than 8% carbohydrate (80 grams per 1000 ml or 34 ounces).

When choosing sports drinks or products, look at the ingredient list. Products with less ingredients have a lower osmolalityand may be better tolerated. Also, specificity in terms of selecting the appropriate gut training fuel source is important. This means that you should train with what you’re going to race with to get the adaptations of the gut to the specific foods or sports products that you’re going to be using.

Finally, consuming carbohydrates during exercise is not only important to provide energy, it can actually help reduce gastrointestinal symptoms by increasing the blood flow to the intestinal area.  For this reason, you should avoid long periods without carbohydrate consumption during prolonged exercise. It is advised to consume carbohydrates early (immediately pre-exercise) and frequently (every 20 minutes) in small amounts according to your tolerance.


Editor’s Note: Article author Kathryn Adel MS, RDN, CSSD recently completed a specialized course from Monash University focusing on exercise and gastrointestinal/IBS symptoms. Read more about her course review in her article, Monash University Food as Medicine Course: Overview & Review.

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