In this blog, Raf Van Dyck, practical assistant and dietitian at Ghent University, provides scientifically grounded insights and practical tools to help you prevent gastrointestinal issues during exercise and improve your gut comfort and performance.
Get to Know Your Gut
It all starts with taking a closer look at what you’re experiencing and where you feel it, as gastrointestinal issues can take many different forms.
Some symptoms affect the upper gastrointestinal tract, including:
- Burping
- Regurgitation
- Nausea
- Upper abdominal pain
- Heartburn
Other symptoms affect the lower gastrointestinal tract, including:
- Lower abdominal bloating
- Excessive gas
- An urgent need to go to the toilet
- Diarrhoea
- Blood in your stool
If you regularly experience these symptoms in everyday life, even when you’re not exercising, there may be an underlying medical condition. In that case, be sure to consult a doctor to rule out conditions such as lactose intolerance, stomach ulcers, Crohn’s disease, ulcerative colitis or coeliac disease. Blood in your stool should always be checked by a doctor.
If your symptoms only occur during exercise, adjusting what you eat and when you eat it can often make a big difference. Below, we break down the key factors you can control to help keep gut issues at bay.
It all starts off the track
Exercise-related gut issues rarely have a single cause. That’s why a healthy lifestyle is essential for good gut health. Make sure you get enough sleep and find the right balance between stress and relaxation.
A balanced diet rich in fibre, antioxidants and fluids is the foundation. You can find these in foods such as:
- Wholegrain bread, oats, seeds and nuts
- Vegetables and fruit
- Water, tea and soups
Your gut microbiome, the community of bacteria living in your gut, also benefits from a healthy diet. These bacteria produce short-chain fatty acids such as acetate, propionate and butyrate. These fatty acids help strengthen the gut barrier, protecting your body against harmful bacteria and substances.
Foods to pay extra attention to:
Some foods are more likely to trigger gut issues than others. They can increase gas production, contribute to blockages or speed up gut motility. Here are a few things to keep in mind:
- Gas-producing foods: mushrooms, cabbage, onions, leeks, peppers, legumes, eggs, fish, beer and carbonated drinks.
- Foods that may contribute to blockages: raw vegetables, asparagus, mushrooms, legumes, nuts and tough cuts of meat.
- Foods that speed up gut motility: coffee, alcohol, carbonated drinks, high-fat meals and gas-producing foods.
FODMAPs, what?!
Some people and athletes are more sensitive to certain types of carbohydrates, known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols). Examples include fructose (fruit sugar), lactose (milk sugar) and xylitol, a sweetener often found in chewing gum. If you’re sensitive to these carbohydrates, eating foods that contain them regularly or in large amounts can trigger gut symptoms.
Monash University has developed the Monash University FODMAP Diet app, which helps you check whether foods are high or low in FODMAPs. You can then try cutting back on certain foods to see whether your symptoms improve or disappear.
When stress and strain hits your gut
Gut issues are more common during high-intensity exercise or prolonged efforts. Race-day nerves can also make things worse. If you experience gut problems during training or competition, take a closer look at the circumstances and what you ate and drank beforehand. This is the best way to identify potential triggers and figure out what works for you.
How you move matters
Your stomach and intestines need a good blood supply to deliver oxygen and nutrients to the tissues. When blood flow is reduced, the gut can become stressed, potentially leading to pain and other physical symptoms.
When running, the repeated impact of each stride puts extra strain on the gut. On the bike, a position that compresses your abdomen and restricts blood flow can also cause problems. That’s why posture and core stability training are important for helping to reduce gut issues during exercise.
Your nutrition plan on race and training days
Before
If you want to start your workout or race with a calm stomach and happy gut, there are three things to consider: what you eat, when you eat and the form your food comes in.
First, not all nutrients are equally easy to digest. Carbohydrates and water are generally well tolerated, while protein, fat and fibre take longer to digest.
Second, timing matters. The bigger the meal, the more time your body needs to digest it. Depending on the size and composition of your meal, aim to eat between 30 minutes and 3 hours before you start. If your meal is high in protein, fat or fibre, give yourself a little extra time.
Finally, texture also plays a role. Drinks, porridges and shakes are generally easier to digest than solid meals containing lots of meat, vegetables and sauces.
During
Drinks tend to put less strain on your stomach and gut than solid foods during exercise. Osmolality matters too. Hypotonic and isotonic sports drinks are generally well tolerated.
The type and combination of sugars also make a difference. Combining glucose and fructose in the right ratio can help reduce the strain on your gut. If you consume 90 grams of carbohydrates per hour, a glucose-to-fructose ratio of 2:1 is ideal. At 120 grams per hour, a 1:0.8 ratio is recommended. It’s also best to avoid carbonated drinks.
You can also train your gut, a strategy known as gut training. The more you practise taking in carbohydrates during high-intensity sessions and under race conditions, the better your gut can adapt and the lower your risk of gastrointestinal issues. Finally, keep an eye on your hydration and make sure you don't start your workout already dehydrated.
After
After exercise, it's important to replace the fluids and add the proteins you've lost. When it comes to food, build things up gradually, moving from liquids to solid foods. You could start with a recovery drink, move on to a banana or rice pudding, and finish with a full meal.
References
Raf Van Dyck – Practical Assistant and Dietitian, Ghent University
- Morton et al, From Metabolism to Medals: Contemporary Perspectives and Revisiting Carbohydrate Guidelines for Fuelling Endurance Athletes During Exercise, Journal of Nutrition 156(5):101442, february 2026
- Prado de Oliveira et al Gastrointestinal Complaints During Exercise: Prevalence, Etiology, and Nutritional Recommendations, Sports Med, 2014 May 3;44(Suppl 1):79–85
- Monash University: www.monashfodmap.com/ibs-central/i-have-ibs/starting-the-low-fodmap-diet/
- Doornink et al., Leidraad voor voedingsdeskundigen bij kanker, 1999
