Exercise and the gut is a complex relationship, moderate exercise has been shown to support the growth of beneficial bacteria in the gut. However, many athletes (particularly runners) may experience changes in their gastrointestinal symptoms during intense exercise.
Some of the reasons you may experience changes in your bowel movements during exercise include:
A reduction of oxygen to the gut
During exercise, oxygen delivery to the working muscles increases which can leave the gut with limited amounts of oxygen.
An inflammatory response to high intensity exercise is very normal, however this inflammation can at times trigger undesirable gastrointestinal symptoms.
- Changes in electrolyte balance
Exercise often causes electrolyte losses through sweat, as a result this can influence homeostatic fluid balance which in turn may contribute to symptoms such as Diarrhea.
These changes are normal and are widely experienced, over-exercising may contribute to making these symptoms worse. However, there are some things you can do ahead of your training session to help limit these gastrointestinal symptoms:
Work with your gut
Ultimately we will all respond to interventions and different foods in a unique way. Try to record how different meals/ foods and drinks make you feel and impact your gut in order to find the best approach for you.
This does not mean you have to go on a low fodmap diet, however if you are exercising a lot and noticing drastic impacts on your gut symptoms limiting your fodmap intake can help with reducing these symptoms.
Staying hydrated helps to limit the impact of electrolyte losses. However, if you are exercising for a prolonged period of time you may want to look at re-fuelling with electrolytes during your session.
Avoid eating too close to exercise
Consuming foods too close to exercise can contribute to impaired gut symptoms as your body is trying to digest the foods with the reduced oxygen which in turn can contribute to impaired digestion and partially digested food entering the gut.
Lis, D. M., Stellingwerff, T., Kitic, C. M., Fell, J. W., & Ahuja, K. D. (2018). Low FODMAP: a preliminary strategy to reduce gastrointestinal distress in athletes. Med Sci Sports Exerc, 50(1), 116-23.
Monda, V., Villano, I., Messina, A., Valenzano, A., Esposito, T., Moscatelli, F., ... & Messina, G. (2017). Exercise modifies the gut microbiota with positive health effects. Oxidative medicine and cellular longevity, 2017.