How not to go number 2 in you wetsuit – Avoiding runner’s diarrhoea

Avoid the toilet challenge!
Avoid the toilet challenge!

Do you suffer from stomach problems when you do excercise or race? This phenomenon is more common than you think. Research is probing and narrowing down its causes making it easier for those suffering from this challenge and it turns out that this problem can be even more challenging for us who do swimrun, in a black tight and warm wetsuit. 

Stomach problems during exercise is common among runners, twice as common compared to other sports like swimming. Problems with your stomach (gastrointestinal) can have great impact on your performance, even making you quit a training session or race. Common stomach problems are:

  • Diarrhoea
  • Reflux
  • Nausea
  • Vomiting
  • stomach pain
  • Belching
  • Bloating
  • Lower abdominal cramps
  • Urge to defecate                 

What exactly causes diarrhoea among runners is still debated in research. Most agree however that causes are multifactorial, but mainly related to ischemic (insufficient blood flow to the gastrointestinal tract), mechanical (vibration and movement of organs), and nutritional factors (food intake before and during the race). There are also strong indicators that some people are genetically more prone to developing symptoms such as diarrhoea.

In general, people are affected differently, ranging from mild to very acute forms. Normally, the majority suffers from a functional type diarrhoea which mainly consists of watery stool. However, in certain cases runners suffer from what is called ‘acute exercise-induced diarrhoea’ also known as ‘Runner’s Trots’, which forces the runner to pass stool immediately and in rare cases suffer from bloody diarrhoea.

Eating gels can become counter-productive!
Eating gels can become counter-productive!

Research suggests that intake of carbohydrates, specifically gel, and during exercise in hot conditions might increase the risk for diarrhoea. Why it’s especially important to have this in mind when swimrunning, since much of the running takes part in a fully closed-up wetsuit which encapsulates and increases the body heat. If the sun is out the day of the race, or if the dead clam and windless, the person prone to stomach problems should be extra careful.

It is recommended that you pay attention to these issues up to 3 days (72 hours) before a race, which is normally the longest time required for the digestive process. If you have a history of suffering from runner’s diarrhoea, avoid intake of known causes at least 3 hours before exercise.


  • Dehydration

Avoid or lower the intake of:

  • Bicarbonate
  • Caffeine
  • Fibre
  • FODMAPs*
  • Fructose (alone)
  • Fat
  • Protein
  • High concentrated carbohydrate beverages
  • Nonsteroidal anti-inflammatory agents (NSAIDs)

  • Be careful when doing exercise or racing in a full closed-up wetsuit
  • Especially in hot climates or when the sun is out.

Ok to ingest:

  • Combining glucose with fructose (carbohydrates)
  • Normal food intake
  • Normal beverages




*Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, are carbohydrates poorly absorbed by the body, usually found in wheat, onions and some dairy products, fruits and vegetables. Exercise caution around this if you are prone to diarrhoea or especially suffering from irritable bowel syndrome (IBS).

If you don’t suffer from runner’s diarrhoea that often. A good advice is to try to test and eat variants of above mentioned food with plausible negative impact, and to do exercise in a controlled environment to try to isolate potential individual causes.

Remember: In swimrun it’s common to travel to races all over the world, why it is likely you end up in a different country with a different food and water culture. It is common for many races to share an evening meal the night before the race, why the key rule should be that if you are prone to stomach problems, not to change your dietary intake close to or the night before race.

Bring your own food or buy products you trust!

Good luck

/The WoS Team

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Runner’s diarrhea: what is it, what causes it, and how can it be prevented?

Curr Opin Gastroenterol. 2016 Oct 27.

de Oliveira EP. Read the full study here.

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