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“
Gut symptoms are common, but they don’t have to derail training. Small, practised tweaks – what you eat, when you eat it, and how you hydrate – usually make the biggest difference.
Featured article from 
Ever had your stomach turn mid-run? You're not alone.
Digestive issues during running – stitch, nausea, bloating or urgent pit stops – are common. In sports science you'll see two terms: Exercise-Induced Gastrointestinal Syndrome (EIGS), which describes changes in gut function during exercise, and Exercise-Associated Gastrointestinal Symptoms (Ex-GIS), which are the symptoms you feel (nausea, cramping, reflux, urgency). These are most often reported in endurance sports like running and triathlon (Costa et al., 2025).
What's actually going on?
During longer or harder efforts, blood is prioritised to working muscles, core temperature rises, and stress hormones tick up. For some runners, that mix can delay stomach emptying and irritate gut lining, especially if you're under-fuelled or dehydrated (Costa et al., 2025). Put simply: the gut is working in tougher conditions than usual.
Common symptoms
- Upper GI: nausea, bloating/burping, reflux.
- Lower GI: cramping (including “stitch”), gas, urgency, loose stools.
If symptoms persist despite basic tweaks, or you notice blood or mucus in stools, or recurrent low iron, B12 or Vitamin D, check in with your GP or a sports dietitian.
Why do gut problems happen on the run?
A few usual suspects tend to combine:
- Exercise stressors: heat, longer or high-intensity sessions, dehydration, pre-race nerves. (Costa et al., 2025; Mountjoy et al., 2023; Santonicola et al., 2019)
- Personal factors: menstrual-cycle shifts, IBS/IBD or undiagnosed intolerances, poor tolerance of planned gels / drinks, poor tolerance of specific gels/drinks, or NSAID use (e.g., ibuprofen) (Costa et al., 2025; Mountjoy et al., 2023; Santonicola et al., 2019)
- Nutrition context: lots of fibre or high-FODMAP foods close to training; low energy availability/REDs; restrictive or disordered eating patterns (Costa et al., 2025; Mountjoy et al., 2023; Santonicola et al., 2019).
Can you “train” your gut?
Yes. Just like legs and lungs, the gut adapts to what you regularly ask it to do. Gradually practising fluid and fuel intake during training can improve tolerance (better gastric emptying and absorption, fewer symptoms) and help performance (Jeukendrup, 2017; Martínez et al., 2023). Think of it as giving your stomach reps, not surprises.
There are several gut training strategies recommended for runners that can be tailored to help improve symptoms. You should always seek the guidance of an Accredited or Advanced Sports Dietitian to monitor and modify accordingly, but some strategies include:
- Training immediately after a meal
- Training with high carbohydrate or solid foods
- Training with increased / large fluid volume
- Increasing daily carbohydrate content of dietary intake
Whilst these strategies may seem counterintuitive or contrary to what is typically advised to avoid pre-exercise, they may support the gut health to adapt which can lead to an improvement in tolerance! (Jeukendrup, A.E., 2019)
Nutrition tips to calm the gut around key sessions:
Go lower fibre the day before hard work
If you're symptom-prone, dial down high-fibre/high-FODMAP foods in the 12–24 hours before a race or big session e.g., large serves of legumes, bran cereals, onion/garlic/broccoli, and bigger nut/seed portions. Keep overall diet for gut health quality high across the week; just shift timing (Burke et al., 2019 & Costa et al, 2025).
Time meals so they help, not fight you
- The night before: a carb-forward dinner tops up muscle glycogen (your go-to fuel for working muscles) (Burke et al., 2019; Murray & Rosenbloom, 2018).
- 1–2 hours before an early session: a small, low-fibre carb snack may feel easier – toast with honey, a banana, dates, or a low-fibre cereal bar.
- 3–4 hours before a later session: a simple meal you digest well – chicken-rice bowl, tofu noodles, pasta with lean protein, eggs on toast – plus easy salad veg (carrot, capsicum, zucchini, leafy greens). Middle-distance and distance papers emphasise practising race-style fuelling so it's familiar on the day (Stellingwerff et al., 2019; Burke et al., 2019).
Hydration and the gut
Even mild dehydration can make a session feel hotter and your gut less happy. A practical pre-exercise guide is about 5–7 mL/kg of fluid roughly 4 hours before exercise; if urine is still dark or you haven't peed, another ~3–5 mL/kg in the 2 hours before may help (ACSM, 2007). In the heat, or if you're a salty sweater, consider electrolytes (Goulet, 2012).
Quick checklist
- Trim high-fibre/high-FODMAP foods in the 12–24 hours before key sessions if you're symptom-prone (Burke et al., 2019).
- Practise small, familiar carbs and fluids on easier runs, then build up, aka gut training (Jeukendrup, 2017; Martínez et al., 2023)
- Start runs well-hydrated using the ACSM guide; add electrolytes for heat/humidity (ACSM, 2007; Goulet, 2012).
- Log what you ate, drank and felt - patterns show up fast.
When to get help
Check in with a GP or accredited sports dietitian if symptoms don't settle with basics, you notice blood/mucus, or you have ongoing fatigue or low iron/B12/Vitamin D. Also, worth a chat if you suspect a food intolerance or if fuelling feels stressful (Mountjoy et al., 2023).
Gut symptoms are common, but they don't have to derail training. Small, practised tweaks – what you eat, when you eat it, and how you hydrate – usually make the biggest difference. If issues linger, personalised support is the fastest path back to comfortable running.
Close-up of person preparing toast with peanut butter and banana, a gut-friendly snack rich in fibre, potassium, and healthy fats for runners.
Disclaimer
The information provided in this article is of a general nature only and is not intended to replace professional medical, health, or fitness advice. It does not take into account your individual objectives, physical condition, medical history, or needs. Before acting on any of the guidance or recommendations provided, you should consider whether it is appropriate for you in light of your personal circumstances. You should always seek the advice of a qualified healthcare professional (such as a physiotherapist, podiatrist, dietitian, or medical doctor) before starting, changing, or relying on any exercise, training, or nutrition program. Rebel Sport accepts no liability for any loss, injury, or damage suffered by any person relying on the information provided.
References
- ACSM. (2007). Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377–390.
- Burke, L. M., Jeukendrup, A. E., Jones, A. M., & Mooses, M. (2019). Contemporary nutrition strategies to optimize performance in distance runners and race walkers. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 117–129.
- Costa, R. J. S., et al. (2025). Sports Dietitians Australia & Ultra Sports Science Foundation joint position statement: Preventing and managing exercise-associated gastrointestinal perturbations and symptoms. Sports Medicine, 55(5), 1097–1134.
- Goulet, E. D. B. (2012). Dehydration and endurance performance in competitive athletes. Nutrition Reviews, 70(Suppl 2), S132–S136.
- Jeukendrup, A. E. (2017). Training the gut for athletes. Sports Medicine, 47(Suppl 1), 101–110.
- Martínez, I. G., Mika, A. S., & Costa, R. J. S. (2023). The effect of gut-training and feeding-challenge on markers of gastrointestinal status in response to endurance exercise: A systematic review. Sports Medicine, 53(6), 1175–1200.
- Mountjoy, M., Ackerman, K. E., Bailey, D. M., et al. (2023). IOC consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57(17), 1073–1097.
- Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243–259.
- Santonicola, A., Gagliardi, M., De Filippis, F., et al. (2019). Eating disorders and gastrointestinal diseases. Nutrients, 11(12), 3038.
- Stellingwerff, T., Måkestad Bovim, I., & Whitfield, J. (2019). Contemporary nutrition interventions to optimize performance in middle-distance runners. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 106–116
