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How to avoid gastrointestinal issues during exercise

Over 50% of endurance athletes complain of gastrointestinal symptoms during an endurance event. 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.


During exercise, our bodies undergo changes to adapt to stress, which can disrupt the digestive system. Several factors may exacerbate digestive symptoms such as the intensity, duration and type of effort; the level of fitness of an individual; the individual’s tolerance of different foods; types and amount of supplements and beverages consumed during exercise; training in the heat and heat acclimation; and taking anti-inflammatory drugs.


Fortunately, it is possible to avoid digestive symptoms during exercise. Here are three aspects to consider:


1.     Start your exercise well hydrated, avoiding both dehydration and over-hydration.

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. Dehydration can increase gastrointestinal issues during exercise. It causes blood volume to decrease, which reduces blood flow to the gut and delays gastric emptying. Also, it reduces the ability of our body to regulate temperature, resulting in greater core temperature. On the other hand, overdrinking to the point of overwhelming the stomach can also lead to GI issues.


When exercising in the heat or sweating excessively, sodium also needs to be replenished. The amount of sodium needed depends on how much you lose through sweat, but also on how much fluid you’re able to drink. If you take in too much sodium and don’t drink enough fluid, this can cause issues as well. Ask your dietitian or coach ways to calculate your fluid and sodium needs.


2.     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 eight weeks before a competition.


You should make sure to consume enough water when consuming gels or other foods. When choosing sports drinks or products, look at the ingredient list. Products with fewer ingredients have a lower osmolality and may be better tolerated. 


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.



3.     Choose low FODMAP foods and drinks before and during exercise.

FODMAP is an acronym for certain natural sugars that are harder to digest and can trigger symptoms in people with irritable bowel syndrome (IBS) or who have a more sensitive gut. In certain cases when digestive symptoms during exercise are severe, following a low FODMAP diet in the days leading up to a race and during periods of intensified training can help reduce gastrointestinal symptoms during and post exercise, whether someone has IBS or not. This is because during an intense or prolonged effort, 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 during your race.


In conclusion, gastrointestinal symptoms in endurance athletes are common but treatable. If this is your case, don’t hesitate to contact your Axes sports dietitian who specializes in gut health to help you develop a plan.



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