Nausea, vomiting, bloating, gut pain and diarrhoea. These are some of the common gut issues experienced by endurance athletes who exercise for more than three hours.
It’s estimated that up to 96% of these athletes experience gut symptoms, which can get more severe and more common the longer they exercise.
The ‘fight-or-flight’ response
Many factors can cause exercise-associated gut symptoms (officially termed “exercise-associated gastrointestinal symptoms, or Ex-GIS); however, it’s primarily due to the “fight-or-flight” response and changes in blood circulation.
In response to strenuous exercise, there’s an increase in activation of the sympathetic nervous system, along with a redirection of blood flow towards working muscles and away from the gut.
As a result, gut function and integrity can be compromised, making an athlete more prone to experiencing gut issues.
Lack of blood flow to the gut can cause damage to the cells, which allows gut contents to enter circulation, including harmful toxins associated with bacteria. In severe cases, this could be fatal if it leads to a systemic inflammatory response and infection.
Exercise can also compromise gut function by delaying movement of food along the gut and impairing its digestion and absorption of nutrients.
Gut problems are further compounded among endurance and ultra-endurance athletes who need to consume a considerable amount of food and fluids during exercise to sustain their efforts.
Current recommendations state that these athletes should aim for an intake of about 30-90 grams of carbohydrates per hour during exercise. But this may mean a greater amount than what an athlete is accustomed to, which can further worsen symptoms and lead to under-fuelling.
In cases when Ex-GIS becomes extremely severe, this can lead to an athlete dropping out of a race.
Better understanding how to train your gut
Much like how challenging exercises and training can make your muscles stronger, it’s thought the gut can also be repetitively challenged in order to improve its tolerance of nutrition during exercise.
Isabel Martinez is a nutrition scientist in Monash University’s Department of Nutrition, Dietetics and Food – and a runner – who’s exploring the benefits of gut training to improve gut function and reduce the gut problems that plague endurance athletes.
Her team is recruiting adults aged 18-55 who are able to complete three hours of running at 60% maximum effort (an easy long run pace with several short breaks); are free from gastrointestinal diseases/conditions; and able to attend assessment appointments and exercise trial days at Monash University’s BASE Facility in Notting Hill.
Findings from the research will help fine-tune nutritional recommendations for athletes, help manage gut issues, and, ultimately, support health and optimal performance.
