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What are the Main Gastrointestinal Problems in Athletes and What Can I Do to Prevent Them?

More marathons are won or lost at the porta-toilets than at the dinner table. Read our guide to gastrointestinal problems in athletes.

Gastrointestinal complaints (or gastro-intestinal problems) are very common amongst endurance athletes and many are aware that running can cause GI problems. An estimated 30 to 50% of distance runners experience intestinal problems related to exercise. Bill Rodgers, marathon legend, with 4 victories in both the Boston Marathon and New York City Marathon in the late 1970s said: "More marathons are won or lost in the porta-toilets than at the dinner table." This illustrates the magnitude of the problem for endurance athletes and in particular long-distance runners and triathletes.

gastrointestinal infographic

Symptoms of GI problems

Gastro-intestinal problems come in many different forms and are highly individual. Some symptoms are mild and don’t have much impact on anything, others can affect performance or even health.

The most common gastrointestinal complaints include:

  • Eructation (belching)
  • Abdominal Pain
  • Nausea
  • Gastroesophageal reflux (or heartburn)
  • Abdominal Cramping
  • Increased Flatulence
  • Loose Stool, diarrhea, and vomiting

The runner's trots

One of the more serious problems is diarrhea. Because diarrhea is so common amongst endurance runners this is also known as the “runner’s trots”. GI-complaints are normally divided into two categories: symptoms of the upper intestinal tract or symptoms of the lower intestinal tract (see infographic).

There is a third category of symptoms that cannot be classified as upper or lower gastro-intestinal problems but might be related to the gastro-intestinal tract (for example stitch). All of the symptoms may be experienced during any type of endurance activity, but they are more common during running compared to cycling. In triathlon, we see many more problems on the run than the swim or the bike. This could be because it is later in event, but it is also related to the up-and-down movements of running.

Prevalence of gastrointestinal problems

In one study, the vast majority (83%) of 471 marathoners who completed a survey reported GI problems occasionally or frequently during or after running: 53% experienced the urge to defecate and 38% reported diarrhea (1). Women were more likely than men to experience these problems.

In another study 1,700 participants were surveyed after a marathon race (2). Lower gastrointestinal symptoms, such as diarrhea, abdominal cramps, urge to defecate, flatulence, and gastrointestinal bleeding were found to be more common than upper gastrointestinal symptoms such as nausea, vomiting, heartburn, bloating, and side ache (stitch).

In yet a study conducted at a long-distance triathlon (Embrunman) we found that 93% of the participants reported at least one symptom of gastrointestinal discomfort. 29% of these symptoms were rated as serious (complaints that would affect exercise performance) (3).

Lower gastrointestinal symptoms are more often observed in women than in men, and some symptoms are more frequently reported by younger people compared with older participants. Problems seem to occur more frequently during running than during activities such as cycling or swimming, possibly because of the vertical (i.e., up and down) movements of the gut during running. Individuals with pre-existing GI issues (such as reflux, lactose intolerance or irritable bowel syndrome) are more likely to get GI-symptoms during competition.

Our final thoughts on gastrointestinal problems

One can argue how reliable numbers are when obtained by different methods and each method will provide different values. However, whatever way one looks at the data via whatever method you trust most, one message is very clear: gastro-intestinal problems are very common and are a frequently quoted reason why a race has not gone according to plan.
In the next article we will look at some of the reasons why these problems occur.
If you are looking for potential solutions to these GI-problems go to this article on prevention of GI-problems.
Note: this blog was adapted from a blog on

If you have any questions about this article, or any other questions - simply reach out to us at We're here to help!


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