Runner’s stomach refers to a wide range of stomach symptoms during, after, or otherwise related to running. People may experience diarrhea, abdominal pain, and cramping.

According to Sports Dietitians of Australia, runners are more likely than other athletes to experience stomach pain during exercise. Various aspects of a runner’s lifestyle, including diet, may also contribute to stomach pain during and after exercising.

While runners may report pain during or after exercise, a 2022 study found that most runners experience symptoms during a run. It showed that 61% of runners surveyed experienced at least one running-related gastrointestinal symptom.

Read on to learn more about what runner’s stomach is, why it happens, and how to manage it.

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Runner’s stomach is a symptom, not a medical diagnosis. It refers to a broad group of symptoms, and people may use the term to describe different experiences.

Some common symptoms people anecdotally report include:

  • diarrhea during a run
  • abdominal pain and cramping
  • the sensation of a stitch or cramp in the side — a symptom doctors call exercise-related transient abdominal pain

Researchers have proposed a number of potential explanations for runner’s stomach. None of the explanations completely explain all cases, so it is likely that several different factors may contribute to it.

Exercise-related transient abdominal pain (ETAP)

ETAP is the stitch in the side many people get when exercising. Researchers still have not conclusively determined its cause.

According to research from 2015, irritation of the parietal peritoneum, which covers the wall of the abdomen, is the most likely cause.

Dehydration

Running can be an intense workout that causes a person to sweat and rapidly lose fluids. Without adequate hydration, a person may develop muscle cramps, vomiting, nausea, and diarrhea. Diarrhea may further dehydrate a person, making symptoms worse.

Diet

A 2022 study that examined the digestive symptoms of runners did not find any correlation between diet and stomach pain. However, foods that irritate a person’s stomach may do so during or after a run.

Sports Dietitians of Australia suggests that high carbohydrate drinks, especially right before a run, may contribute to stomach pain. This is because these drinks pull extra water into the gut, exacerbating symptoms.

Reduced blood supply

Early in a run, the body has to pump more blood to the muscles. This reduces blood supply to the digestive tract, impairing digestion and potentially causing stomach pain.

This may be one factor contributing to ETAP, but it could also explain diarrhea.

Rarely, a person may develop a more serious complication. Ischemic colitis means that a person develops serious digestive distress from lack of blood flow. This can cause diarrhea and abdominal pain.

A 2017 study of 17 active runners found that running induces changes in the way the intestines absorb nutrients. Specifically, a 90-minute challenging run increased intestinal permeability.

While this suggests that running may affect digestion, it is not a complete explanation. There were no differences in intestinal permeability between those with and without symptoms of runner’s stomach.

Because researchers do not fully understand runner’s stomach — and because several different issues may contribute to the phenomenon — there is no surefire strategy for preventing it.

However, some tips that may help include:

  • Hydrate leading up to and during a run, but avoid very sweet beverages.
  • Do not eat heavy meals right before a run.
  • Train in advance for a run to build the body’s tolerance.
  • Avoid fiber, protein, and other slowly digested food before a run. Instead, eat a small carbohydrate-rich meal.

For some runners, an upset stomach continues to last after the run. Others may experience discomfort after the run ends. This is not distinct from runner’s stomach and has many of the same causes.

However, it is important for runners to note that not all cases of stomach pain are from runner’s stomach. Any chronic or severe stomach pain may signal a serious underlying condition, even if it frequently coincides with running.

A person should contact a doctor if they have:

  • stomach pain, bloating, or diarrhea that does not improve
  • bloody diarrhea
  • vomiting along with signs of dehydration, such as a very dry mouth or sunken eyes
  • stomach pain that does not resolve with home care
  • intense stomach pain along with a fever

Doctors do not fully understand runner’s stomach. They do not know what causes it, and there is no evidence that a single cause accounts for all cases.

Instead, it is likely that several different factors, and potentially an interaction between these factors, may explain the phenomenon.

Many different issues can cause digestive pain, so it is important to seek medical care for chronic symptoms.