Foods to Avoid Before a Marathon: A Race-Week Nutrition Guide for Endurance Runners

Race week nutrition can make or break your marathon. While most runners focus on carb loading, the foods you avoid in the 48-72 hours before the gun are just as critical. From Saturday night curries to innocent-looking granola for breakfast, the wrong meal at the wrong time can trigger bloating, cramps and unwanted bathroom stops mid-race. Here's the science-backed guide to what to cut and what to eat instead.

Table Of Contents

• Why Your Gut Struggles On Race Day

• Foods To Avoid

• Takeaway Food To Avoid

• What To Eat Instead

• Take Home Points

Why Your Gut Struggles On Race Day

Between 30-90% of distance runners experience GI symptoms during hard efforts¹. During intense running, blood is redirected away from your gut to working muscles, slowing digestion and increasing gut sensitivity¹˒². Add pre-race nerves and the mechanical jostling of running and your digestive system is already under stress before you've eaten a thing. What you eat in the 48-72 hours before the gun can make or break race day.

Foods To Avoid

High-Fibre Foods

Fibre slows gastric emptying and increases fermentation gas in the colon. In race week, swap wholegrain bread, brown rice, bran cereals, and raw salads for their low-residue white equivalents³.

High-Fat & Fried Foods

Fat is the biggest delay of gastric emptying, a rich, fatty meal can still be sitting in your stomach on race morning¹˒³. Avoid fried food, cream sauces, cheese-heavy dishes, and fatty cuts of meat in the 48 hours before racing.

Spicy Foods

Capsaicin irritates the gut lining and can trigger cramping, heartburn, and urgency, even in runners who handle spice well day-to-day¹˒².

Fermentable Foods: Beans, Legumes & Cruciferous Vegetables

Beans, lentils, broccoli, cauliflower, and cabbage contain indigestible carbohydrates that gut bacteria ferment into gas. Humans lack the enzyme to break down raffinose-family oligosaccharides in legumes, so they reach the colon intact and produce bloating and flatulence⁴.

High-FODMAP Foods

Cutting high-FODMAP foods for a few days before your race has been shown to reduce bloating and unwanted toilet stops in most runners who try it⁵⁻⁸. Key high-FODMAP foods to limit: apples, pears, watermelon, mango, onion, garlic, large portions of wheat, and lactose-heavy dairy.

Unfamiliar Foods & Low-Carb Meals

Never eat something new before a race. Novel foods introduce untested gut triggers, and if you're racing away from home, pack your go-to pre-race foods³. Equally, avoid low-carb meals, the Academy of Nutrition and Dietetics/ACSM recommends 10-12g of carbohydrate per kg of body weight over the final 36-48 hours for male marathon runners, while female athletes benefit from around 8g/kg/day given a slightly lower sensitivity to carbohydrate loading, provided total energy intake is adequate³˒¹¹.

Takeaway Food To Avoid

• Indian curries → high fat (ghee, cream) plus capsaicin spice: a double hit of slowed digestion and gut irritation¹˒⁹.

• Raw poke bowls → High in fibre from raw vegetables and also likely high in FODMAPs due to ingredients such as edamame, onion and garlic.

• Large bowls of oats or muesli → oats contain fermentable beta-glucan; muesli adds dried fruit, nuts, and seeds, significantly raising the fibre load

• Bean burritos → legumes, raw onion, garlic, and chilli salsa combine fibre, FODMAPs, and spice.

• Creamy pasta → the pasta is fine; carbonara or alfredo-style sauces are not. Stick to a simple tomato-based sauce.

• Thai Food → coconut cream, chilli, same problem as Indian.

• Falafel/hummus wraps → chickpea-heavy, high fibre and FODMAP.

• Açaí/smoothie bowls → May contain high-FODMAP fruits, granola, seeds. If you're having a smoothie or açaí bowl, keep it small, stick to low-FODMAP fruits like banana and blueberries, and skip the granola, dried fruit, and honey toppings.

What To Eat Instead

Keep it familiar, high-carb, low-fat, and low-fibre¹⁰.

• Night before → white pasta with tomato sauce, white rice with lean protein, baked potato, plain bread rolls

• Race morning (1-4 hrs out) → white toast or bagel with honey or jam, banana, rice cakes. Aim for 1-4g carbohydrate per kg body weight³.

• Golden rule: if you haven't eaten it before a long run in training, don't eat it before your race

Take Home Points

• Strip fat, fibre & spice 48-72 hrs out

• Avoid fermentable foods

• Skip the risky takeaways

• Carb-load with familiar, low-residue foods

• Nothing new on race day, or the day before

Ash Miller
Dietitian and Nutritionist (Masters)
Bachelor of Physical and Health Education
Instagram: @ashthomo_nutrition

References

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4. Winham DM, Hutchins AM. Perceptions of flatulence from bean consumption among adults in 3 feeding studies. Nutr J. 2011;10:128.

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7. Wiffin M, Smith L, Antonio J, Johnstone J, Beasley L, Roberts J. Effect of a short-term low-FODMAP diet on exercise-related gastrointestinal symptoms. J Int Soc Sports Nutr. 2019;16:1.

8. Parnell JA, Wagner-Jones K, Madden RF, Erdman KA. Dietary restrictions in endurance runners to mitigate exercise-induced gastrointestinal symptoms. J Int Soc Sports Nutr. 2020;17:32.

9. Great Run. What to eat before a run [Internet]. Great Run; 2024 [cited 2025]. Available from: https://www.greatrun.org/training/what-to-eat-before-a-run/

10. Sports Dietitians Australia. What to eat before, during and post exercise [factsheet]. Melbourne: Sports Dietitians Australia; 2024. Available from: https://sportsdietitians.com.au/Article?Action=View&Article_id=6

11. Lebrun CM, Rumball JS. Recommendations for healthy nutrition in female endurance runners: an update. Front Nutr. 2015;2:17.

Disclaimer:

The content in this blog is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always speak with your doctor or allied health team before changing your diet, exercise, or taking supplements, especially if you have a health condition or take medication. Please use this information as a guide only. Aid Station doesn't take responsibility for individual outcomes.