Written By

Dr Emily Jevons

3 minutes

Your nutrition has the power to make or break your event which is why it’s so important to get it right.


Gut, gastrointestinal complaints, often referred as GI issues, are known to be relatively common in athletes of all levels, recreational to elite, particularly (but not limited to) in endurance sport. Research has estimated a huge 30-50% of endurance athletes experience symptoms such as diarrhoea, abdominal pain, cramping, bloating, nausea, heartburn or even vomiting (de Oliveira et al, 2014).

Reasons for gastrointestinal complaints can be due to a few different factors. Physiological due to changes in blood flow as the body redirects blood flow from the digestive system to your working muscles, psychological due to feelings of anxiety, mechanically (movement specific) such as the up and down motion of running or the tight position of a TT bike can put pressure on the abdominal region and finally, nutrition.

Certain foods or drinks can irritate the gut during exercise, this is highly individual and is why it’s so important to find out what works for you. Undigested carbohydrate can lead to bloating, gas production and delayed stomach emptying.

Dehydration has also been linked to increased gastrointestinal issues as it leads to reduced blood supply to the gut.

Usually, such gastrointestinal issues will have a detrimental effect on how you feel, how much fuel you then want to continue taking on and your physical performance.

One way you can minimise GI issues is by having a planned & practiced fuelling strategy that you know works for you and your gut. This is why practicing your fuelling strategy in training and adopting a ‘nothing new on race day’ mindset is key.


Just like other muscles in the human body, you can train your gut over time. This will improve your tolerance to food, carbohydrate supplements and fluid intake during exercise and helps develop your bodies capacity to absorb and digest carbohydrate during exercise (Cox et al, 2010; Jeukendrup, 2017).

The general principle of training your gut involves starting with small quantities and gradually increasing over time so your body can adapt and lean to accommodate greater volumes of food and fluid. Research has shown even 2 weeks of gut training can improve gut symptomology and consequentially, performance (Costa et al, 2017).

We recommend trying to implement the following when training your gut:

  1. Training shortly after a meal (or sooner than you normally would) and eating solid foods during training to get used to exercising with food in your stomach.
  2. Gradually increasing the amount of carbohydrate you consume every hour during training, using your chosen products. For example, if you were going to use our GO Isotonic energy gels for your event, you could start by trying 1-2 gels per hour (22-44g of carbohydrate per hour), building up to 3-4 gels per hour (66-88g of carbohydrate).
  3. You should also be drinking regularly during training to ‘train the stomach’ and encourage faster stomach emptying, especially if your event is going to be in warmer conditions where you know you will need to consume fluids more often than normal.
  4. Choose the right sessions to practice and be consistent. Identify your longer or more race specific sessions throughout the week and use though to practice your fuelling strategy. Consistency is key to adaptation.

Be patient and give this process time, we are not referring to trialling your nutrition the week before your event, we’re referring to a few weeks, sometimes months before for some individuals.


A common mistake that’s made with race-day fuelling is thinking more is better. Try to stick to your strategy that you have tested beforehand. More fuel does not equal better performance and consuming too much can trigger unwelcomed gastrointestinal symptoms if you’re not used to consuming this amount.


Costa RJS, Miall A, Khoo A, Rauch C, Snipe R, Camões-Costa V, Gibson P. Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Appl Physiol Nutr Metab. 2017 May;42(5):547-557. doi: 10.1139/apnm-2016-0453. Epub 2017 Mar 22. PMID: 28177715.

Cox GR, Clark SA, Cox AJ, Halson SL, Hargreaves M, Hawley JA, Jeacocke N, Snow RJ, Yeo WK, Burke LM. Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. J Appl Physiol (1985). 2010 Jul;109(1):126-34. doi: 10.1152/japplphysiol.00950.2009. Epub 2010 May 13. PMID: 20466803.

de Oliveira EP, Burini RC. Carbohydrate-dependent, exercise-induced gastrointestinal distress. Nutrients. 2014 Oct 13;6(10):4191-9. doi: 10.3390/nu6104191. PMID: 25314645; PMCID: PMC4210913.

Jeukendrup AE. Training the Gut for Athletes. Sports Med. 2017 Mar;47(Suppl 1):101-110. doi: 10.1007/s40279-017-0690-6. PMID: 28332114; PMCID: PMC5371619.

Written By
Dr Emily Jevons
Dr Emily Jevons
Emily has worked with Science in Sport since 2021. With a PhD in Exercise Physiology & Nutrition, she currently provides nutritional advice for endurance athletes. Emily not only understands the science behind performance nutrition solutions, but also the physiological and psychological demands of sport after competing competitively in swimming and triathlon for a number of years.
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