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Runner's Stomach: What Causes It and How to Avoid It
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Runner's Stomach: What Causes It and How to Avoid It

As many endurance athletes will know, there’s nothing quite as inconvenient as an unexpected bout of runner’s stomach mid-race. 

The sensation might come in the form of a stabbing pain in the side, a wave of nausea or a strong urge to run quickly to the toilet. 

The good news is that runner’s stomach can be preventable or you can at least reduce its severity by ensuring you’re making sensible dietary choices prior to and during training and remaining hydrated throughout your training.

This blog will discuss the main causes of runner’s stomach and digestive issues in endurance athletes and offer solutions to prevent or relieve symptoms when training or racing.

What Is Runner’s Stomach?

Runner’s stomach is a common digestive issue experienced by long-distance runners and endurance athletes.

It’s defined as a range of gastrointestinal (GI) distress symptoms occurring before, during or after exercise, including cramping, bloating, nausea, diarrhoea, vomiting and pain. 

Runner’s stomach is estimated to impact up to 90% of long-distance runners. Whilst running is the most documented form of exercise linked to these digestive issues, GI problems are also common in other endurance sports such as cycling or triathlon.

What Causes Runner’s Stomach

During prolonged exercise, the body prioritises supplying oxygen to the muscles in use; this is achieved by redistributing blood flow away from the GI system e.g. the stomach and intestines. 

This can be problematic for digestion, causing exercise-induced GI syndrome due to the reduced ability of the GI system to function efficiently. 

However, there are also many other factors that can contribute to a higher likelihood of experiencing runner’s stomach.

Caffeine Bullet Founder David Hellard finishing a race

Impact of Sport and Type of Exercise

The type of GI issue you experience can vary depending on your sport.

Running places more stress on the abdomen and stomach due to the higher impact forces on and jostling, which has been linked to lower GI symptoms such as bloating and diarrhoea.

Cyclists are known to more commonly experience upper GI symptoms like acid reflux. This is likely due to the forward-leaning position necessary for bike riding which creates pressure on the stomach area.

Poor Food Choices and Improper Timing of Fuelling

Eating the wrong foods at the wrong time can massively increase your risk of experiencing GI discomfort during exercise.

For example, eating high-fiber or high-fat foods too close to starting a workout will leave you feeling bloated and full, due to a slower rate of gastric emptying (the movement of food from your stomach to your intestines).

In addition, taking gels or energy drinks without water during exercise can also contribute to distress. Taking in highly concentrated carbohydrates such as gels can draw excess water into the gut that may result in diarrhoea.

Recommendations on Food Type and Timing for Pre-Exercise Fuelling

The American College of Sports Medicine recommends consuming 1-4 g/kg bodyweight of carbohydrates 1-4 hours before endurance exercise to “top-up” muscle glycogen stores.

  • Overnight oats with banana, berries, and almond milk
  • White toast with jam
  • Low fibre cereal with low-fat milk

Multiple studies suggest consuming 30 to 60 grams of carbohydrates per hour for endurance exercise lasting more than 1 hour to maintain blood glucose levels and delay fatigue.

This is generally quite easy to achieve through the use of sports drinks, energy gels and energy chews. However, more nuanced strategies will likely be required for ultra events.

Caffeine Bullet Founder David Hellard running in a park


When dehydration occurs during exercise, it may worsen existing gastrointestinal symptoms in addition to impairing athletic performance. 

There are several reasons why this might happen; most notably, dehydration reduces the amount of fluid available to support digestion and could lead to more intense gut pain and discomfort. 

Dehydration also causes decreased circulation throughout the body, further reducing blood flow to the GI system, potentially increasing the severity of GI distress.

For sessions shorter than 4 hours and in non-extreme weather conditions (e.g. high temperatures and humidity), drinking to thirst during the run is sufficient in most cases, as long as you aim to intentionally rehydrate post-run.

Post training, you should replenish the fluid volume lost during your session, this can be estimated by weighing yourself before and after your session to estimate fluid lost as sweat. A fluid volume (usually 1.5x) greater than that lost in training is necessary to fully restore water balance.

However, for longer sessions (4+ hours) or sessions in hot and humid conditions where sweat rates will be higher it is recommended to follow a hydration strategy throughout. For example fluid volumes of 450–750 mL per hour are recommended.

To minimize the likelihood of hyponatraemia (low blood sodium levels), electrolytes (mainly sodium) may be needed in concentrations greater than that provided by most commercial products.

If sweat rate is extremely high, aim to consume fluids containing higher amounts of sodium. This can be accomplished using electrolyte tablets or even by adding small amounts of table salt (about 0.5 grams per litre) to your drinks.

Not Using Ginger During Training

Ginger has a long history of use as a remedy for nausea and vomiting, particularly in the context of pregnancy-induced morning sickness. 

Most popular exercise supplements have very little evidence to support their use. However, recent research suggests that ginger is an effective natural remedy for a range of forms of nausea and vomiting. 

How Ginger Can Prevent Nausea

A 2015 study conducted at Heriot-Watt University found that ginger can alleviate nausea experienced during endurance exercise. Symptoms of nausea and gastric issues increased during exercise in all groups, however they significantly decreased after exercise in the group that consumed an intra-exercise beverage containing ginger extract. With the ginger beverage reducing perceived nausea and gastric distress scores by approximately 10% when compared to the placebo beverage. The mechanism behind this effect is believed to be related to ginger’s antagonistic effects on serotonergic 5HT receptors.

It’s important to note, that in this study, participants were only involved in a 5k run,  where significant GI issues are not typically expected. Therefore, the study primarily showed the impact of ginger on post-exercise nausea and GI distress rather than during the exercise itself. In longer-duration events, where GI issues are more likely to arise, the beneficial effects of ginger would likely be even more pronounced and alleviate issues during exercise as opposed to after exercise.

How Ginger Can Improve Digestion

Ginger is also commonly used to promote digestion and aid in mitigating gastrointestinal discomfort.

Ginger can significantly enhance digestion by speeding up gastric emptying – the journey of food from our stomach into the small intestine. A sluggish gastric emptying process can lead to discomfort and bloating due to the sensation of a fuller stomach, so ginger can be used to provide substantial relief.

Ginger also promotes contractions in the antrum, a region at the lower end of the stomach. These contractions are crucial in the digestion process as they help mix food with stomach acid and digestive enzymes, breaking down food into a more digestible form. This can facilitate more efficient nutrient absorption and decrease instances of indigestion and discomfort.

The 2020 systematic review conducted at the college of pharmacy at Seoul National University also analysed seven randomised controlled trials that investigated ginger’s effect on gastric function, primarily focusing on gastric emptying. All studies reported that ginger enhances gastric emptying. In addition, research suggests that ginger’s enzymes can help break up and expel gas formed in the intestinal tract during digestion, relieving discomfort.

For endurance athletes, this could have a significant impact, as faster gastric emptying is likely to reduce stomach discomfort during long training sessions or races, making it easier to consume more fuel and maintain comfort throughout the duration of exercise.

However, convenient and easy to take ginger supplements during exercise are hard to come by, that’s why we created ginger roars. We combined raw ginger with virgin coconut oil, cassava root and cane sugar. The result? A full flavoured energy solution that will help prevent digestive issues during training and racing. Each 33mg caffeine chew will help settle your stomach when you’re struggling to take on board fuel.

Ginger Roars close up shot of individually wrapped chew on a chopped piece of ginger

How to Settle Your Stomach Before Your Next Training Session

Runner’s stomach can be a challenging issue for endurance athletes, but with the right strategies, you can take steps to settle your stomach and prevent discomfort during your runs. Here’s a summary to help you prepare effectively:

Optimise Your Carbohydrate Intake Pre-Training:

Before training, it’s crucial to consume enough carbohydrates for energy. The American College of Sports Medicine suggests 1-4 g/kg of body weight of carbs 1-4 hours prior to endurance exercise. This tops up muscle glycogen and provides sustained energy.

Stay Hydrated:

Hydration is vital for performance and digestion. For sessions under 4 hours and in moderate weather, drink to thirst during the run. Afterward, replenish lost fluids by weighing before and after the session and consuming 1.5x sweat loss in fluids.

Opt for Low Fibre and Low Fat Foods Pre-Workout:

Choose wisely to avoid GI discomfort during exercise. Skip high-fibre and high-fat foods before workouts as they slow digestion. 

Incorporate Ginger Into Your Nutrition Plan:

Ginger reduces nausea and aids digestion. Add it to pre-run routine via ginger chews or beverages. It improves digestion and gastric emptying, reducing discomfort during your run.




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