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Nutrition6 min read

Gut training for runners

Stomach problems are one of the most common reasons runners slow down or drop out of long races. Your gut adapts to what you regularly give it during exercise. Practising race fuelling in training, and building it up step by step, means you can take more carbohydrate with fewer problems on race day.

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A trail runner drinking from a soft flask with gels in his hydration vest.

The short answer

Gut training means practising carbohydrate intake on long runs so your gut adapts. Start 6–10 weeks before your race at about 30–40 g of carbohydrate an hour, and raise it by about 10 g an hour every week or two towards your race target. Use the same gels and drinks you will use on race day.

  • Practise at race pace on some sessions: the gut copes less well at higher intensity.
  • Never try a new product or a much bigger amount for the first time on race day.

What is gut training?

A gut training plan for a marathon

An example progression on one or two long runs a week. Move on only when the current amount feels comfortable.
Weeks before the raceCarbohydrate per hour on long runs
10–930–40 g
8–740–50 g
6–550–60 g
4–360–75 g, using a glucose and fructose mix
2–1Your race target, at race pace on at least one run

Find your race target with the race nutrition planner, then use this plan to build up to it. Fill your stores beforehand with a proper carb load.

How to avoid stomach problems when running

  • Use the exact gels, chews and drinks you will use on race day.
  • Take gels with water, not with a strong sports drink.
  • Take carbohydrate little and often, every 15–20 minutes, rather than all at once.
  • Eat a lower-fibre, lower-fat meal 2–4 hours before long runs and races.
  • Practise drinking from cups if your race uses them.

Above 60 g an hour, mixing glucose and fructose lets more carbohydrate in, because they use different routes through the gut wall (Jeukendrup, 2014). Learn more about drink strength in isotonic, hypotonic and hypertonic drinks explained.

When stomach problems need a doctor

Thinking of cutting carbohydrate instead? See what keto does to athletic performance.

People also ask

How long does gut training take?

Most plans run for 6–10 weeks before a race, although your gut keeps adapting as long as you practise regularly.

Can you train your gut to take 90 g an hour?

Many runners can reach 90 g an hour with practice and a glucose and fructose mix. Build up gradually and stop going higher if it causes problems.

Should I gut train on every run?

No. One or two long runs a week is enough. Shorter, easy runs do not need fuelling.

What if gels always upset my stomach?

Try a different product, take smaller amounts more often, and drink water with them. Sports drinks or chews may suit you better.

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Scientific References & Evidence

  1. Cox, G.R., Clark, S.A., Cox, A.J., Halson, S.L., Hargreaves, M., Hawley, J.A., Jeacocke, N., Snow, R.J., Yeo, W.K. and Burke, L.M. (2010) 'Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling', Journal of Applied Physiology, 109(1), pp. 126-134. doi: 10.1152/japplphysiol.00950.2009. Available at: https://doi.org/10.1152/japplphysiol.00950.2009
  2. Jeukendrup, A. (2014) 'A step towards personalized sports nutrition: carbohydrate intake during exercise', Sports Medicine, 44(Suppl 1), pp. S25-S33. doi: 10.1007/s40279-014-0148-z. Available at: https://doi.org/10.1007/s40279-014-0148-z
  3. Jeukendrup, A.E. (2017) 'Training the gut for athletes', Sports Medicine, 47(Suppl 1), pp. 101-110. doi: 10.1007/s40279-017-0690-6. Available at: https://doi.org/10.1007/s40279-017-0690-6

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Educational information for adults aged 18 and over. It does not diagnose, treat or manage any medical condition. If you have a health condition, or symptoms that worry you, speak to your doctor or a health professional.