How to Prevent Digestive Issues During Exercise

Kathryn Adel February 19, 2019 Practical Tips, SFW

Did you know that more than 50% of endurance athletes suffer from gastrointestinal issues during an endurance event such as a marathon or a triathlon? Reported symptoms include nausea, vomiting, gas, bloating, stomach pain, an urge to defecate, and diarrhea. Here are three aspects to consider to avoid gastrointestinal issues during exercise!

When we begin to exercise, our body undergoes changes to adapt to the stress induced by the effort, which can disrupt the digestive system. When starting exercise, there is an increase in blood flow to the muscles to provide them with the oxygen and nutrients that they need during physical effort. As a result, there is less oxygen available to the gastrointestinal system, which causes damage and inflammation to the intestines. There is also a stimulation of the sympathetic nervous system, which reduces the rate of digestion and can thus affect the transport of nutrients. This means that if you consume carbohydrates or other nutrients before or during exercise, they may be poorly absorbed. Malabsorption of protein and carbohydrate can also occur after exercise when consuming a recovery beverage or snack.

Several factors may exacerbate digestive symptoms such as: the intensity, duration and type of effort, the level of fitness of an individual, the tolerance of the individual to different foods, types and amount of supplements and beverages consumed during exercise, training in the heat and heat acclimation, as well as taking anti-inflammatory drugs. Fortunately, it is possible to avoid digestive symptoms during exercise. Here are three aspects to consider!

1) Begin your exercise well hydrated, and avoid dehydration or overhydration

When digestive discomfort occurs during exercise, there is a tendency to associate these symptoms with foods, beverages or supplements that have been consumed. However, it may be simply your level of hydration that is responsible! Indeed, dehydration causes a decrease in blood volume, which reduces blood flow to the intestines and delays digestion. Dehydration also decreases the body’s ability to regulate its temperature, thereby increasing body temperature. On the other hand, drinking too much can also cause digestive issues. Studies show that a proper level of hydration before and during exercise can reduce the frequency of digestive symptoms and reduce the malabsorption of nutrients contained in the pre-workout meal.

The American College of Sports Medicine recommends drinking 5 to 10 ml of fluid per kilogram of body weight two to four hours before exercise to optimize hydration levels. Light colored urine (such as lemonade) is a good indicator of adequate hydration levels. However, it should be noted that taking certain vitamins can make the urine darker. During physical exercise, it is advisable to drink regularly, according to one’s thirst. Finally, consuming cold beverages when exercising in the heat can also help reduce digestive symptoms.

2) Train your intestines to tolerate carbohydrates during exercise

Consuming carbohydrates during prolonged exercise (lasting over an hour) is recommended to maintain blood glucose levels, provide energy, reduce fatigue and improve sports performance. On the other hand, if your digestive system has not been accustomed to absorbing and digesting carbohydrates during exercise, carbohydrates can be poorly absorbed, leading to digestive symptoms. So, it is essential to practice consuming carbohydrates during workouts. The type of carbohydrate is important, which means that during your workout, you should the same supplements (gels, drinks, etc.) that you plan to use in competition. Generally, your tolerance to carbohydrates during exercise should improve from week to week. If this is not the case, you should try other kinds of supplements. When choosing a supplement, look at the ingredient list. A supplement that contains fewer ingredients is generally better tolerated. It should be noted that consuming carbohydrates during exercise can also help reduce digestive disorders by increasing blood flow to the intestines. Thus, consuming a small amount of carbohydrates more often during exercise (for example, taking a sip of a sports drink or an energy chew (Clif Blok, Sport Bean) every 20 minutes rather than a gel every 45 minutes) can potentially help increase carbohydrate tolerance during exercise in people who have more difficulty tolerating them.

3) Reduce your fiber and FODMAP intake for a few days before your race

The term FODMAP is an acronym for certain categories of sugars that are not completely absorbed by the small intestine, and instead ferment in the colon, which can thus produce digestive symptoms. More specifically, the sugars concerned are lactose, fructose, sorbitol, mannitol, fructans and galacto-oligosaccharides. People who have irritable bowel syndrome (IBS) are particularly sensitive to FODMAP. On the other hand, studies suggest that during prolonged and intense effort, tolerance to fermentable carbohydrates may be reduced, leading to malabsorption and digestive discomfort in some individuals who generally tolerate these types of sugars. Thus, if you have experienced severe digestive symptoms with exercise, it may be worthwhile trying to reduce your intake of fiber and FODMAP-rich foods for a few days before an important sporting event. So, for example, instead of eating spaghetti with tomato sauce and garlic bread the day before a race, you might want to choose rice with chicken and a small amount of vegetables instead.

Author

Kathryn Adel

Kathryn holds a Bachelor Degree in Nutrition as well as a Bachelor and a Master Degree in Kinesiology, all from Laval University. She is a Registered Dietitian and active member of the Ordre professionnel des Diététistes Nutritionnistes du Québec (ODNQ) and of the American Academy of Nutrition and Dietetics. She holds the Monash University's certification for the FODMAP diet and IBS, and has considerable clinical experience in that area. She is also an accomplished athlete, having ran track and cross-country at a national level. Kathryn specializes in sports nutrition, weight loss, diabetes, as well as heart and gastrointestinal health.