Runner’s Diarrhea (Trots) What is it and How to Prevent it?

About Runner’s Diarrhea

Runner’s diarrhea is frequent, loose and often watery stool that may occur during or after a long distance run, workout, occasional run, or fast walk (1). It is also commonly referred to as runner’s trots. The exact cause of runner’s diarrhea is not known although there are several theories as to why this phenomenon does occur. While it is not always severe, it can exacerate dehydration that arises with long distance running or other strenuous physical activity.

Read more on diarrhea after exercise.

To a large extent runner’s diarrhea can be prevented but not always. It is usually not serious if short-lived and properly managed. Simple measures are sufficient to prevent complications until the diarrhea resolves. As far as possible, antidiarrheal medication should not be used. Sometimes diarrhea may be due to an infection and the watery stool is one way to flush out the microbes and its toxins.

Causes of Runner’s Diarrhea

Runner’s diarrhea does not only affect professional runners or athletes. In fact this type of exercise-induced diarrhea may even occur with other types of sports, exercises and strenuous physical activity.  It can sometimes even result in diarrhea during the racing event. In these cases it is important to reconsider the viability of completing the race as severe dehydration is more likely.

While the exact cause of runner’s diarrhea is unclear, it is believed to be due to the following factors:

  • Vigorous and uncharacteristic movement of the intestines during running can increase bowel motility. Furthermore tensing of the abdominal muscles may increase intra-abdominal pressure.
  • Blood flow being redirected from the gut to the legs which reduces bowel activity and may impair digestion if a meal was consumed shortly before running.
  • Stress, which may trigger pre-existing irritable bowel syndrome (IBS). This may affect professional athletes in particular due to the psychological stress of competing.
  • Dehydration which arises with any strenuous physical activity in itself may not lead to dehydration. However, inappropriate rehydration may cause water to remain in the bowels or draw water out of the body into the bowels which can then lead to watery diarrhea.

The strain on the body with certain events can increase the likelihood of certain infections, such as gastroenteritis. Therefore the diarrhea that develops following a sport event may not be due to the strenous physical activity. Instead it is a result of an infection or sometimes even other causes of diarrhea that are unrelated to running.

Prevention of Runner’s Diarrhea

The following steps before, during and after the run may help prevent runner’s diarrhea. It is important to note that medical intervention is necessary if there dehydration has arisen and is not easing with oral rehydration. It is always advisable to consult with a sports physician prior to any major race, even if there are no major health concerns.


At least TWO DAYS before the run the following foods should be avoided:

  • High-fiber foods like legumes (beans, soy, peas, lentils), cabbage, cauliflower, large amount of cereals, to avoid excessive bloating.
  • Fat-rich foods like pork, bacon, pizza and most of other fast foods, cakes, olives, nuts, chocolate, which are hard to digest and may stay in the bowel for long periods of time.
  • Dairy, including yogurt, cheese and icecream, especially if lactose intolerant.
  • Fructose-rich foods: honey, grapes, apples, pears, mango, stone foods (like peaches, cherries), dried fruits (like prunes, raisins, figs, dates), jams, fruit juices or any fruit product from mentioned fruits; sorbitol (in “sugar free” chewing gum, “low calorie foods”, some carbonated beverages or sport drinks); also avoid other “polyols” (read labels), like xylitol, maltitol, mannitol, isomalt.  For further explanation read about fructose malabsorption.
  • Hot spices, like pepperoni, which may irritate the bowel;
  • Alcohol, because it causes dehydration even before the event.

Generally safe foods before running are bread, corn products, rice, pasta, poultry, potatoes, bananas, citruses (lemons, oranges), moderate amounts of green-leafy vegetables, soups and broths.

Picture 1. Marathon runners

At least TWO HOURS before the run:

  • Have a bowel movement if possible, and do not eat anything more until the end of the run.
  • Small amounts of oral rehydrating solutions can be helpful but do not drink copious amounts at one sitting.


  • Drink enough water or oral rehydration solutions (ORS). Sports drinks that are specially formulated for atheletes are also acceptable.
  • Avoid hot drinks or drinks sweetened with sorbitol or xylitol, carbonated drinks, caffeine, alcohol. Fruit juices should also be avoided during the event.
  • Never consume water and other fluids from questionable sources. This includes rivers, lakes, streams, public faucets or from individuals who are not at rehydration stations or officially elected to provide hydration services.


Proper rehydration during this time is crucial in preventing runner’s diarrhea as well as other complications such as diarrhea. Rehydration should ideally involve the use of an oral rehydrating solution. This contains the optimal concentration of fluid and electrolytes that are properly absorbed in the gut and replenishes the fluid and salts lost with sweating. If there is severe dehydration then an intravenous (IV) drip for fluid replacement may be necessary.

Read more on oral rehydration solutions.

Attempting to rehydrate with fruit juices, sodas, caffeinated beverages like tea or coffee, or alcohol can be a problem. It may trigger or aggravate runner’s diarrhea. It may also worsen dehydration. The problem with these beverages is that it does not contain the optimal concentration of fluid and electrolytes. This poses a problem in the body that already has undergone stress and dehydration.

Fluids may not be absorbed from the gut into the body (osmotic diarrhea) or may be drawn out from the body into the gut due to a disturbance in electrolyte concentration. The increased water volume in the bowels can thereby lead to diarrhea. Furthermore substances like caffeine not only dehydrate the body but may stimulate the already active bowels which can worsen diarrhe and hasten dehydration.

Related Articles:


  1. Runner’s diarrhea  (
About Jan Modric (209 Articles)
Health writer

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