Your race fuel needs practice

A gel in your pocket is only useful if you can eat it. Gut training means repeatedly practising food and fluid intake around exercise. The aim is to tolerate the fuelling your event requires. [1] [8]

Why your stomach objects

Long or hard exercise can reduce blood flow to the gut and disturb its movement and absorption. Heat adds strain. Running also adds mechanical movement. Symptoms have several possible causes, so one bad gel rarely explains the whole picture. [2] [8]

Nausea, bloating, cramps and diarrhoea can interrupt fuelling or end a race. The dose, the drink concentration and your existing tolerance matter alongside the effort and conditions. [1] [2] [8]

What the studies show

In a randomised trial of 25 runners, two weeks of carbohydrate practice reduced gastrointestinal symptoms compared with placebo. A separate trial of 18 runners also found fewer symptoms and less carbohydrate left unabsorbed after two weeks. [4] [5]

Those trials used repeated feeding during running, including 90 g of carbohydrate per hour. They involved small groups and controlled sessions. Their results do not establish that every runner should start at that dose. [4] [5]

A 2023 systematic review found eight eligible studies, with interventions lasting 4–28 days. Results supported better comfort and possibly less incomplete absorption. They did not establish a standard protocol or prove protection against intestinal injury. [6]

Choose an intake you can practise

The 2016 joint sports-nutrition position stand gives 30–60 g of carbohydrate per hour for exercise lasting 1–2.5 hours. For efforts beyond 2.5–3 hours, it gives up to 90 g per hour. These ranges guide event fuelling. Your starting intake needs to reflect what you already tolerate. [3]

At higher intakes, the carbohydrate mix matters. Glucose and fructose use different intestinal transport pathways. Combining them, sometimes labelled multiple transportable carbohydrates, allows more ingested carbohydrate to be used than glucose alone at high doses. Maltodextrin supplies glucose. [1]

A glucose-fructose mix still needs practice. Your effort, race duration and tolerance should guide the plan with a sports dietitian when needed. A longer race does not make the highest hourly intake compulsory. [1] [3] [8]

Give practice several weeks

Two weeks is a tested intervention length. It is not a proven minimum, a deadline for adaptation or a guarantee. The best frequency, progression and duration remain uncertain. Much of the research includes men, which limits generalisation. [4] [5] [6]

Leave several weeks before your race to repeat and adjust your fuelling. This is a practical planning choice based on the trials, rather than a validated schedule. Fit practice into training you already tolerate. [1] [4] [5] [6]

Rehearse during your runs

Use the following as a rehearsal checklist. It translates the research into practice, but the sequence itself has not been tested as a programme. [1] [6] [8]

1. Start from an amount you already tolerate on a familiar run. Write down the product, carbohydrate grams, fluid volume and timing. Count carbohydrate from drinks as well as food. [1] [3] [8]

2. Spread intake through the session and use the planned drink concentration. Repeat it before increasing the amount. Change one thing at a time so your notes remain useful. [1] [8]

3. Rehearse the breakfast, gels, drinks or foods you expect to use. Include practice at a representative effort and on relevant terrain within your existing training. A comfortable easy run cannot confirm tolerance for every race condition. [1] [8]

4. Record symptoms during and after the run, alongside effort and weather. If symptoms increase, review the dose and conditions before progressing. Persistent or severe symptoms need assessment by a qualified clinician. [6] [8]

For example, 20 g every 30 minutes totals 40 g per hour. That is arithmetic for a rehearsal, not a universal recommendation. Choose the starting amount from your own tolerance and fuelling needs. [3] [8]

Low-FODMAP has a narrower role

FODMAPs are fermentable carbohydrates that can be poorly absorbed and contribute to gas and bowel symptoms. Reducing selected foods before a race is a different strategy from practising carbohydrate intake during running. [7] [8]

In a crossover trial of 11 runners, six days of low-FODMAP eating reduced daily symptoms. Symptoms during exercise did not differ significantly from the high-FODMAP condition. A quieter stomach during the week is not proof of better race tolerance. [7]

The 2025 position statement supports considering a short 24–48-hour reduction before exercise for symptom management. It also reports that symptom relief and markers of intestinal injury can move in different directions. [8]

Discuss this with a sports dietitian if symptoms recur. Rehearse any changes before race week and preserve enough energy and carbohydrate. Broad, long-term food restriction is not the gut-training goal. [3] [8]

Take a practised plan to the start

Gut training can improve comfort, but individual responses vary. Faster gastric emptying during exercise and the exact adaptations behind symptom improvements remain uncertain. The evidence cannot promise a symptom-free ultra or a particular finish time. [6] [8]

Choose food you have used, an amount you can tolerate and a rhythm you have rehearsed. Adjust from what happened in training. [1] [8]

References

[1] Jeukendrup AE (2017). Training the Gut for Athletes. Sports Medicine 47 (Suppl 1), 101–110. DOI.

[2] Costa RJS, Snipe RMJ, Kitic CM, Gibson PR (2017). Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics 46(3), 246–265. DOI.

[3] Thomas DT, Erdman KA, Burke LM (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics 116(3), 501–528. DOI.

[4] Costa RJS, Miall A, Khoo A, Rauch C, Snipe R, Camões-Costa V, Gibson P (2017). Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Applied Physiology, Nutrition, and Metabolism 42(5), 547–557. DOI.

[5] Miall A, Khoo A, Rauch C, Snipe RMJ, Camões-Costa VL, Gibson PR, Costa RJS (2018). Two weeks of repetitive gut-challenge reduce exercise-associated gastrointestinal symptoms and malabsorption. Scandinavian Journal of Medicine & Science in Sports 28(2), 630–640. DOI.

[6] Martinez IG, Mika AS, Biesiekierski JR, Costa RJS (2023). The Effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise: A Systematic Literature Review. Sports Medicine 53, 1175–1200. DOI.

[7] Lis DM, Stellingwerff T, Kitic CM, Fell JW, Ahuja KDK (2018). Low FODMAP: A Preliminary Strategy to Reduce Gastrointestinal Distress in Athletes. Medicine & Science in Sports & Exercise 50(1), 116–123. DOI.

[8] Costa RJS, Gaskell SK, Henningsen K, et al. (2025). Sports Dietitians Australia and Ultra Sports Science Foundation Joint Position Statement: A Practitioner Guide to the Prevention and Management of Exercise-Associated Gastrointestinal Perturbations and Symptoms. Sports Medicine 55, 1097–1134. DOI.

Trailwise is not a medical device. Neither is it a replacement for a doctor or a physiotherapist. Trailwise flags what is worth a conversation. It does not diagnose, and it will tell you when it does not know.