Gut Upsets in Runners- What Does the Science Say?


Poo happens! That dreaded urge to poo on the run or even worse! Most experienced runners have been caught out at some stage in training or racing, we all know that feeling and dread it! In fact the research suggests 30-42% of runners experience the urge for a bowel movement and 14-27% have actually experienced diarrhoea while running.  We all hate that sense of knowing “will I be able to hold on till I get home, make a public toilet or even that thick bush over there”.  I always carry a few folds of toilet paper in my laces on every morning run just in case. While I’ve never been caught out in a race like the poor guy in the photo, poo can happen.

Claire and I recently spent three days chatting to veteran runners at the Expo in the three days leading up to the Gold Coast Marathon. While it’s not conducive to a fast half-marathon, it did highlight to me how many runners suffer from the ‘runs’ and also how many carry injuries into events. I’ve thus decided to write two articles – one on gut upsets and how to avoid them and the other on what science says about preventing running injuries.

The Gut during Exercise

Sport science has shown a lot happens to the gut when we exercise. These changes include:

  1. A reduction in duration, frequency and size of gut contractions during harder intensity exercise – this means absorption of foods is reduced during harder runs.
  2. Transit time of food is reduced during harder runs – again meaning less absorption and gravity pushing out what’s in the gut.
  3. Blood flow to the gut is lowered by up to 60-70% meaning food is not absorbed as quickly.
  4. Dehydration lowers this already reduced blood flow even more, again compromising absorption.

Runners with pre-existing gut conditions such as irritable bowel syndrome or lactose intolerance often suffer runner’s runs. They should be making every effort to see a sports physician or sport dietician.

 Preventing Gut Upsets during Exercise

Below are a swag of scientifically-based recommendations that might minimise gut upsets during training and racing. If you suffer from the runner’s runs, try these one at a time to see what might work for you. If you still have issues, get along to a professional for advice.

  • Keep a food diary to know which foods may trigger the gut upset and experiment dropping the risky foods out of the diet. Typical culprits include fruit juices, fresh or dried fruits, beans, lentils, milk, grain breads, cereals.
  • Use low fibre liquid meal supplements the day before competition.
  • Avoid solid food in the three hours leading up to training or racing.
  • Use liquid food as the pre-competition meal.
  • Before and if needed during exercise, use high glycemic index, low-fat/protein foods that are emptied from the gut quickly.
  • Use sports drinks that are isotonic rather than too rich (fruit juice, milk, soft drinks) before and during exercise.
  • Be hydrated as dehydration has been linked to gut upsets.
  • Sip rather than guzzle water or sports drinks.
  • Train using the drinks you plan to use in racing.
  • Train using the foods you plan to use in racing.
  • Avoid high fibre foods and caffeine before training or racing.
  • Avoid artificial sweeteners including diet drinks and sugar-free gum that contain sorbitol that can lead to diarrhoea.
  • Develop a routine of emptying the bowel before training in the morning.
  • Try a high fibre meal the night before to speed up the transit time – I use muesli combined with plenty of water and it always works a treat – up and go!
  • Have an anti-diarrhoeal tablet (e.g. Imodium, Kaopectate, Pepto-Bismol) before racing or training and follow the instructions on the pack.
  • Know where the toilets are on your run route and run easy to the first one before you run harder.
  • Try running at different times of the day to the normal time that always leads to the runs!

 Sources: Clark, N. (2010). Undesired sideliners: side stitches and runner’s trots. Running & FitNews, 28(4): 21-23.

Fallon, K. (2010). Athletes with gastrointestinal disorders. In Burke, L. & Deakin, V. (Eds) Clinical Sports Nutrition. Sydney, McGraw-Hill.