Episode 117 – Training The Gut For Endurance Athletes

Key Topics Covered

Endurance athlete running

Why This Matters 

  • Carbs are the best fuel source for higher-intensity endurance activities.
  • The best endurance athletes in the world are typically consuming ~90g of carbs per hour. Some can even tolerate more than this.
  • It is almost guaranteed that if you went to 90g of carbs per hour without building up to it, you would run into GI issues. 
  • Quick note that this 90g of carbs is NOT just glucose. This is likely limited to 60g in isolation.
  • To absorb 90g of carbohydrates per hour, this will need to be a combination of glucose and fructose.


  • Reduced feelings of “fullness” if the body gets used to this (this is relevant for both fluid intake and carbs).
  • Improved ability to absorb and oxidize carbohydrates. The intestine literally increases the amount of glucose transporters if it is exposed to them more. 
    • This is why it doesn’t make work to go low carb prior to an event and then take on a high amount of carbs during the race.
  • Improved carbohydrate-specific gastric emptying. 

Strategy to Build up Carbohydrate Intake

  • We typically recommend starting low e.g. 30g of carbs per hour, and then build from there. 
  • Almost everybody is capable of starting at 30g per hour.  
  • It’s probably best to try this on a slightly lower intensity session e.g. don’t introduce it for the first time for a session where your pace is at its quickest.
  • This is also unnecessary to do for every session. Starting with 1-2x per week makes sense. 

Alternative Options 

energy gels

  • Try different gels.
  • Most energy gels are about 21-25g carbohydrates.
  • Try different combinations of fluids and gels.
  • Always drink water alongside gels – most are designed to be consumed alongside ~250ml of water.
  • Trial different frequencies e.g. whole gel all at once vs spreading it out over longer periods.
  • Simply consume less carbs. Not everybody will get up to 90g of carbs. 
  • Potentially consider other things that could be contributing to GI upset e.g. FODMAPs.


  • Due to only having limited carbohydrate storage internally, performance in endurance training and events can be improved by consuming carbohydrates during the session.
  • It is also unlikely that someone who has never consumed intra-training food will be able to tolerate a high enough amount of carbs per hour to optimize performance.
  • However, this can be improved through training your gut tolerance.
  • Start low and gradually build up until your tolerance matches the number of hourly carbs required to optimize performance.

Relevant Links / Resources

Studies Mentioned

Relevant Blogs