How to avoid stomach problems on the run

One of the most common questions runners ask is: ‘How can I prevent or cope with stomach problems during training and races?’ It’s not an issue many of us like to talk about openly, but it's one that’s surprisingly common among runners.

It is estimated that 30 to 50 per cent of endurance athletes experience gut problems related to exercise. The most debilitating and annoying of these issues seems to be the sudden and overwhelming need to evacuate your bowels. In cases of extreme frequency or discomfort, this is known as runner’s diarrhoea or ‘runner’s trots’. Other common problems include abdominal pain and cramping, belching, bloating, nausea, heartburn, flatulence and vomiting. In a study at Maastrict University, in the Netherlands, 93 per cent of triathletes had at least one gastrointestinal (GI) symptom, of which 29 per cent were serious enough to affect performance.

One reason why stomach problems are particularly common in runners is the repeated and sustained up-and-down movements, which literally shake and loosen all the food inside your gut. This is exacerbated by a reduced blood flow to the intestines as more of your blood is diverted to your exercising muscles.

Even if you’re fine during training, you may experience stomach discomfort or an urge to ‘go’ shortly before a race. This is a natural response to stress as your body goes into ‘fight-or-flight’ mode. Stress hormones are released and the digestive process slows or even stops temporarily so that the body can divert all its internal energy to facing a perceived threat.

Certain foods may irritate the gut – for example high intakes of fibre, fat, protein or fructose. Dehydration or consuming a drink that has a concentration of carbohydrate tha you're unaccustomed too can also add to the stress on the gut.

But you can fight back! Here’s how to avoid stomach problems and pit stops while running:

  • Doing a short warm-up run before a race, or a warm-up loop around your house before a training session, can help to get things moving. Alternatively, having a little food or a warm drink before a morning run may have a similar effect and enable you to empty your bowels before you head off. Experiment with training at different times of the day to find out what works best for you.
  • Reduce your intake of high-fibre and gas-producing foods the day before, as well as the day of, a race. Common culprit foods include bran cereals, cruciferous vegetables (such as cabbage, cauliflower and broccoli), beans, lentils and caffeine. For some people, energy gels and bars can cause problems, as can high-fructose foods and drinks. Fructose is absorbed relatively slowly from the gut and, in high concentrations, (especially in the form of a drink) can cause GI symptoms.
  • Start your workout or race fully hydrated. Some athletes avoid drinking in the misguided belief that it causes GI symptoms whereas, in fact, dehydration may be the culprit.
  • If you experience any discomfort when using sports drinks, experiment a little. You could, for example, make them more diluted during training runs, although this approach isn't practical during races, unless you plan to carry your own fluids.
  • Train your gut by regularly consuming carbohydrate foods or drinks during long runs (more than 60 to 90 minutes). Start with very small amounts then gradually increase the amount and frequency. It is possible to increase the number of carbohydrate transporters in your gut so that you become better able to digest and absorb carbohydrate during exercise.
  • Experiment to find what works for you. During training and racing, sports nutrition products – such as bars, gels and chews – are designed to boost your energy but if you consume more carbs than you're used to, you may increase the risk of stomach problems.
  • It may take quite a bit of ‘trial and ‘error’ but by practising your race fuelling and hydration strategy during training there will be less risk of problems on race day.

Anita Bean ( is a registered nutritionist, specialising in sports and exercise, a health writer and former champion athlete. She is the author of more than 20 books, including The Complete Guide to Sports Nutrition and The Runner's Cookbook, and a regular speaker at our Meet the Experts event.