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Running from the runs

The good news is the gut is highly adaptable and your endurance training is helping you in more ways than one.

Running from the runs


Last updated: 02-Mar-16

Written by Sports Dietitian Rin Cobb

If you’ve ever found yourself out on a run, seeking out the nearest toilet rather than the next checkpoint, you’re not alone. Gastrointestinal (GI) issues affect a significant number of runners, which is not only distressing but can put an end to a race before it’s even begun. So why are some affected more than others and what can you do about it?

Your GI tract extends from your mouth down to your stomach, through the small and large bowel and ending at your anus. The main job of your GI tract is to digest and absorb all the nutrients you get from your diet so your body can use them as needed, whilst removing the remaining waste products. Understandably if this process is interfered with, it can lead to a number of less desirable symptoms.

GI distress has many forms from heartburn to stomach cramps to the dreaded runners trots and as many as 20-50% of you report some degree of distress during training or more commonly on race day. Unfortunately, figuring out the cause can be quite complex as I’m sure you’ve already discovered, if you’ve been troubled with gut issues before. Physiological, mechanical and nutritional factors all seem to play a part and it’s more than likely a combination of these that lead to someone becoming symptomatic, which could also help explain inconsistencies in symptom type and frequency.

Table 1: GI symptoms associated with running
Upper GI symptoms Lower GI symptoms
Reflux/heartburn Intestinal/lower abdominal cramps
Belching Side ache/stich
Bloating Flatulence
Stomach pain/cramps Urge to defecate
Nausea Diarrhoea
Vomiting Intestinal bleeding



As you run, blood flow is redistributed away from your gut to the exercising muscles to deliver the increased need for oxygen and other nutrients so you can keep going. As you run harder and for longer, this reduced blood flow to the gut increases, which could be why endurance runners complain of GI issues more so than other athletes. Ultimately if the gut is not getting an adequate supply of blood, it cannot work as it should and gut function will be compromised.


Gastric jostling as you run can in itself lead to more lower GI symptoms and that urgency to dash behind the nearest bush, however it can also damage the gut. Combined with a reduced blood flow, this could be why some runners experience more severe GI bleeding resulting in bloody stools.


Trigger or treatment, nutrition can have a major role to how your gut performs on the day. Type of food, timing of your last meal before you run, caffeine and dehydration can all affect your bowels.  Meals higher in fibre, fat and protein take longer to digest so can increase the risk of GI symptoms and is one reason why low fibre options are generally recommended if increasing your carb intake for the few days before a race. Dehydration reduces your overall blood supply so it can have a further knock on effect to your gut’s blood supply. 

There are a number of runners who cut out various foods from their diet believing they have an intolerance of some sort. However, if the gut is compromised from the exercise you're doing, it’s going to struggle to process food the same way so rather than cutting out foods such as wheat and dairy altogether, try limiting these around race day if you feel they are causing you issues on the run and don’t forget to substitute them so you don’t miss out on all the other essential nutrients they provide.

Gut Training

The good news is the gut is highly adaptable and your endurance training is helping you in more ways than one such as increasing blood flow to the gut, tolerating larger volumes of fluid and improving the flow of nutrients through the gut. Runners who routinely eat on the go also report less symptoms so factoring in a nutrition strategy to your runs will not only provide a readily available fuel supply but could also help prevent tummy troubles come race day. For those that really struggle to eat on the go try building this in gradually, having little and often whilst using simple foods like plain biscuits, bananas or malt loaf and not forgetting carb based drinks as a source too. 

Table 2: Guidelines to help prevent GI problems during running

Meal timing

Aim to have your pre-event meal 2-4hrs before exercise & only a light snack or fluids in the 1hr before; if racing early in the morning could have your large meal the night before and a light snack in the 1hr before

Meal type

Ensure low in fat & protein

Avoid high fibre in the day or days before competition


Avoid dehydration; aim to start exercise well hydrated (straw coloured pee)

More effective to drink throughout the day before competition rather than large boluses on race day

Use isotonic sports drinks (4-8% carbohydrate) for optimal fluid & carbohydrate absorption

High sugar

Avoid high sugar drinks (>10% carbohydrate) pre & during competition

Avoid high fructose foods & drinks pre competition


Avoid lactose pre competition & use alternatives; lactose free, soya or nut


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