Can you train your gut to handle carbs?

I’ve written a few times (1, 2, 3, 4) before about how important it is to ingest carbs training-and-performancewhile racing a distance that takes over ~40-60mins to enhance performance. There still seems to be some resistance to doing this; some of it is fueled by pseudoscience, but some is fueled by the very legitimate concern that ingesting 30-60g of glucose/hour will cause GI distress and potentially an even more detrimental impact on performance.

There’s no doubt, GI distress is often caused by factors other than the carbs ingested during the race (such as ingesting slowly absorbed, slowly metabolized fat, protein or fibre in close proximity to or during a race). So before trying to fix your carb situation, first make sure that it is indeed your problem.26210901325_c79c2657a5_k

Training the Gut

Now, if it really is the carb ingestion that is triggering your GI distress, hope is not lost! We do have the ability to adapt and train our guts to be more tolerant to what we are ingesting.

Take for instance this study. In the study, 25 athletes were put through a “gut-challenge trial” where they ran for 2 hours at 60% of their V02max while consuming 30g of carbohydrates every 20 minutes. They also were told to conduct a 1-hour max effort time trial afterwards.

Participants were then put into one of three 2-week gut-training groups: gel-discs (like the gels and gummies we use on race day), food, and placebo (no carbs). These individuals regularly used each of their assigned fuel source during their training throughout the 2-week procedure.

Then, after 2 weeks of training the gut, this is what they found:

  • GI distress symptoms reduced by 60% in the disc group and 63% in the food group (both of which was significantly greater than the placebo group).
  • The concentration of glucose in the blood was highest in the gel-disc trained group during the second trial.

In other words, if you practice ingesting carbs while running, you will have a decreased chance of developing GI issues and the sugar will be more bioavailable in your blood to run faster.25606221024_709f6077f0_k

Does training the gut actually make us faster?

As we know, just because something should make us faster based on the physiological changes we see, that does not mean it always makes us faster. Fortunately for us, this study also looked at the 1-hour TT. This is what they found:

  • Gel-disc trained runners improved their performance by 5.2%
  • Food-trained runners improved by 4.3%
  • Placebo-trained runners showed a 2.1% decrease in performance

Practical applications:

All of us should be consuming 30-60g of carbs/hour if the race is long enough. If GI problems have limited you in the past, slowly getting your stomach used to the carb source you will use on race day is the way to go.

That is not to say that you should use gels during every run. There is a whole other body of evidence that shows benefits related to conducting fasted workouts to enhance fat oxidation and decrease how much you actually need to deplete your glycogen on race day.

A good way to implement these two contrasting methods of workout fueling is:

  • Fuel your key longer quality sessions and long runs with ~30g of carbs/hour of work (aim for 60g/h on race day).
  • Reserve 2-3 of your easy/ recovery runs to be fasted.
  • In the 2-4 weeks leading into your A-race, conduct 1-2 runs/week where you ingest 60g of carbs/hour. This is a good opportunity to try different flavours and brands to see what works best for you.

When it comes to longer races, nobody can run at their absolute best without the help of sugar! For those of you who have been turned off of ingesting carbs on race day, I hope this study helps re-establish some motivation to train your gut and find a solution that works for you.


  • Patrick S May 4, 2017 5:32 pm

    Hey Sean,

    What constitutes a fasted state here?

    Is fasting defined as “not ingesting carbs during the run”? Or something more extreme, like “not ingesting carbs for several hours (or more?) before or during the run”?

    I ask because I want to know the best way to benefit from those 2-3 fasted recovery runs per week during training with the least amount of discomfort, and the most amount of delicious, delicious sugar.

    • Dr. Sean Delanghe May 4, 2017 6:13 pm

      Hey Pat,

      Good question. In general, if you are well fed in the 12+ hours leading up to the run, your glycogen will be topped up, and not consuming carbs during isn’t enough to reap the benefits of a fasted run.

      A good way to do a fasted run would be to eat a light-to-normal sized dinner early in the evening, and then go for a morning run without consuming anything beforehand. 12-15hour without food followed by a run is a good way to rely on more fat metabolism throughout the run and reap said benefits. So long story short: more than just not consuming carbs during. I hope this helps!

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