If you’ve ever had to make an emergency bathroom stop mid-run or felt nauseous halfway through a race, you’re not alone. Gastrointestinal (GI) problems are incredibly common among runners - from mild bloating and cramping to more severe issues like diarrhea or vomiting. While these symptoms can be frustrating (and sometimes embarrassing), they’re often a result of the unique stress running places on your body, especially your gut. The GI system plays an important role in the delivery of carbohydrates and fluid during exercise. GI problems are experienced by 30-65% of long-distance runners, which tells us that gut function is not always optimal during prolonged exercise.
Common symptoms of runners' gut:
- Stomach cramps
- Bloating
- Nausea
- Acid reflux
- Diarrhea
With Cape Town Marathon just around the corner, this article will discuss the causes of runners gut, as well as some nutrition strategies to help prevent this from happening to you.
Potential causes for runner’s gut include:
- Mechanical jostling of the internal organs from the impact of running (this can be shown by studies that demonstrate increased lower GI symptoms in runners compared with cyclists)
- Reduced blood flow to the gut during exercise, when blood flow is redirected to the working muscles. (At rest, about 1.56L of blood goes to the digestive organs per minute. During intense exercise, that amount drops sharply to just 0.3L per minute).
- Increased stress hormones (several chemical and hormonal changes occur in response to endurance running, that are implicated in GI disturbances, such as increases in cortisol, adrenaline and noradrenaline).
- Overheating and dehydration (dehydration further reduces blood flow to the gut, with runners who lost 4% or more of their body weight in their sweat being more likely to experience GI symptoms)
The role of nutrition in preventing runner’s gut:
Nutrition plays a crucial role in preventing runner's gut. Proper dietary choices can significantly reduce the likelihood of symptoms such as cramping, bloating, nausea, and urgent bowel movements. Avoiding high-fibre, high-fat, and overly processed foods in the 24–48 hours before a run can help minimize digestive stress. Hydration is equally important, as dehydration can worsen gastrointestinal distress. Additionally, timing meals appropriately, usually finishing solid food intake at least 2-3 hours before running, allows the digestive system to process food efficiently. By focusing on a well-balanced, runner-friendly diet and developing a personalized fuelling strategy, athletes can greatly reduce the risk of runner's gut and improve overall performance.
Training Your Gut:
Athletes often overlook the critical role of the GI tract in performance, particularly during prolonged exercise, where efficient delivery of fluids and carbohydrates is essential. Endurance sports frequently trigger GI symptoms like cramping, bloating, and diarrhea, which can impair nutrient absorption and hinder performance. However, research suggests that the GI tract is highly adaptable, and targeted nutritional strategies, referred to as “gut training”, may enhance nutrient delivery and reduce these symptoms.
Different methods for training the gut include training with large volumes of fluid or immediately after a meal, training with higher carbohydrate intake during exercise, simulating your race-day nutrition plan, and increasing the carbohydrate content of your day-to-day diet. The image below from a study by Jeukendrup et al. (2017) summarizes the different strategies and their effects:
Practical tips and summary:
Pre-run fuelling:
- Limit fibre-rich foods and gas-forming foods
- Experiment with liquid meals before racing
- Avoid caffeine if this makes your symptoms worse
- Avoid spicy foods
- Keep well-hydrated
- Try to use the bathroom before the race
- Opt for a tried-and-tested pre-race breakfast
- Avoid high-fat foods
Pre-race breakfast ideas:
- Oats with banana and honey
- Crumpets with jam or syrup
- White toast with peanut butter and banana
During your run:
- Don’t try anything new on race day - practice your race day nutrition beforehand
- Avoid caffeine-containing gels if they upset your stomach
- Drink plenty of fluid with electrolytes
- Avoid artificial sweeteners
Conclusion:
Runner’s gut may be common, but it’s not inevitable. With the right preparation and nutrition strategies, you can minimize the risk and run your best race. By understanding the causes, training your gut, and making smart dietary choices before and during the Cape Town Marathon, you’ll give yourself the best chance of avoiding GI distress. Remember, what works is highly individual, so practice your nutrition plan well in advance and don’t experiment on race day. A calm, well-fuelled gut could be the difference between a tough run and a personal best.
References:
Costa, R. J. S., Miall, A., Khoo, A., Rauch, C., Snipe, R., Camões-Costa, V., & Gibson, P. (n.d.). D r a f t Gut-training: The impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. https://mc06.manuscriptcentral.com/apnm-pubs
