How Triathletes Can Overcome GI Distress

By Ashleigh Libs | Feb. 27, 2018, 3:19 p.m. (ET)
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Gastrointestinal (GI) distress is an ailment many endurance athletes face but is often not talked about or researched as extensively as other, less common problems in this population. Up to 60 percent of endurance athletes have reported experiencing a variety of gastrointestinal symptoms. These can include (bloody) diarrhea, vomiting, nausea and abdominal pain. Experiencing these symptoms can cause an athlete to underperform and can impact one’s ability to recover. 


Gastrointestinal symptoms can be caused by a variety of things; however, three of the most common are discussed below.
Blood Flow
Biologically, gastrointestinal distress often occurs in endurance athletes because of the redistribution of blood flow. This means that blood will flow to the “working muscles” such as the heart, skeletal muscle and lungs more than the gastrointestinal tract during high-intensity exercise. When this happens, the GI tract cannot function as well, which leads to the adverse symptoms athletes often report.
Mechanical Changes
The type of activity can impact an athlete’s susceptibility to GI symptoms because of the impact and posture required. For example, runners experience symptoms more often than cyclists. This is because running puts greater stress on the GI system. Also, there can be changes in gut motility, which is how the GI tract contracts to move food through the system. 

Nutritional Factors
Several nutritional factors have been identified to increase incidence of GI distress in some individuals. Fiber, fructose, fat and protein have all shown some adverse effects in research by making a person more susceptible to these symptoms. 
“One of the biggest mistakes I see that contribute to GI distress include overeating prior to race day (the thinking of ‘having to load the tank’),” sports dietitian Dina Griffin said.
Finally, not consuming adequate fluids prior to and during exercise can exacerbate gastrointestinal issues. 

Basic Tips for Preventing and Overcoming

  • Consume food/beverage with multiple forms of carbohydrates. For example, consuming a beverage with both glucose and fructose may reduce the incidence of symptoms.
  • “Train the gut” by following a nutrition and fluid regimen throughout training to increase tolerance of the items before or during events.
  • Avoid highly concentrated carbohydrate beverages (>10%).
  • Consume familiar foods on race/event day. As Griffin states, it is important to “mimic what has been well-practiced throughout training (leading up to race day)” in order to perform at the athlete’s peak. 
Prado de Oliveira, E and Burini, R (2011). Food-dependent, exercise-induce gastrointestinal distress. Journal of the Internation Society of Sports Nutrition 8:12.
Prado de Oliveira, E. Burini, R., Jeukendrup, A. (2014) Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med; 44 (1): S79-S85.
Gary WK Ho (2009). Lower gastrointestinal distress in endurance athletes. Current Sports Medicine Reports 8:2.
“Gastrointestinal Distress in Athletes” by Peak Performance Nutrition
Ashleigh Libs is currently a master’s student in nutrition with a sports concentration at the University of Utah. She received her bachelor’s degree in dietetics, with a minor in psychology, from the University of Dayton (Ohio). She has experience working with the University of Louisville’s football team and the University of Dayton’s soccer, women’s volleyball and baseball teams. Her goal is to help people/athletes discover what works for them nutritionally to reach their performance goals. You can get in touch with Ashleigh by emailing her at

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.