Train Your Gut to Tolerate Gels: A Practical Guide for Runners
Learning to train your gut is probably the most overlooked part of preparing for a long race, and it is what separates a good race from an afternoon desperately looking for a toilet. If you have ever had nausea, cramps or a stomach shutdown after taking a gel mid-race, the gel is rarely to blame. What happens is that your digestive system isn’t used to processing carbohydrates while you run. And your gut can be trained just like your legs. In this guide I explain how to do it step by step.
Why your stomach rebels when you take gels
When you run at a certain intensity, your body sends blood to the working muscles and takes it away from your digestive system. Your gut gets less blood flow and its ability to process food drops sharply. If at that moment you give it a very concentrated gel it isn’t used to, digestion stalls and you get nausea, bloating, cramps or an urgent need for the toilet.
The interesting part is that your ability to absorb carbohydrates during exercise can be improved. The more you get your gut used to receiving carbs on the move, the better it handles them. That is what we mean by training your gut.
What it means to train your gut
It means gradually getting your digestive system used to tolerating and absorbing carbohydrates while you exercise. You are after two things. The first is tolerance, so your stomach accepts having food in it while you run without complaining. The second is absorption, so your gut can take in more carbs per hour instead of leaving them sitting in your stomach.
Both improve with practice. A trained gut lets you take in more energy during a race without paying for it, and in a long race you notice that in your pace over the final kilometers.
Five steps to train your gut
The idea is to build up over several weeks, without rushing.
Step 1: start to train your gut weeks ahead
Your gut doesn’t adapt in two days. Start several weeks before your goal race and use your long runs to practice. It is a gradual adaptation, like any other.
Step 2: practice on your long runs
The golden rule of race nutrition is to try nothing new on race day, and this is where you follow it. Use your runs and long runs to take gels, drinks or chews exactly as you will in the race. Training is your lab.
Step 3: increase the amount gradually
Don’t go from taking nothing to three gels an hour. Start with a small amount and build up week by week once your stomach handles it well.
Step 4: try different products and formats
Not every stomach tolerates the same things. Try brands, textures (liquid gel, thick gel, chews, drinks) and formulas until you find what suits you. What works for your training partner may not work for you. If you are curious about carb types, I have guides on maltodextrin and lactate gel.
Step 5: rehearse timing and hydration too
Timing counts as well. Practice taking carbs regularly from the start, without waiting until you are out of energy, and always with water, because it helps absorption and reduces discomfort. I go into more detail in the guide on hydration and electrolytes.
How many carbs you should be able to handle
It depends on the length and intensity of your race, so there is no universal figure. The sensible approach is to be clear about your target for race day and work toward it in the weeks before.
To get that number you can use our race carb calculator, which gives you an estimate based on your expected time. That figure is the goal, and training your gut is how you get to tolerate it without problems.
If you want to read the research, PubMed has the studies on how to train your gut for endurance sport.
This all fits with the guide on what to eat before, during and after a race. A trained gut is what lets you get the “during” part right.
Mistakes that slow adaptation
The most common one is leaving it until the end. Starting the week before the race doesn’t give you time to adapt. The second is increasing the amount too quickly and causing exactly the discomfort you want to avoid.
I also see a lot of people practicing only on easy runs. Blood flow to the gut drops most at race pace, so you need to rehearse there too. And don’t forget water, or switch on race day to whatever gel the aid stations hand out if you trained with a different one.
Conclusion
Taking the time to train your gut gives you an advantage anyone can have and very few use. Start weeks ahead, practice on your long runs, increase the amount little by little, find the product that suits you and rehearse when to take it, along with water. In a long race, being able to eat without your stomach complaining saves you a lot of bad kilometers. Choose well, run better.
Frequently asked questions
What does training your gut mean in running?
Gradually getting your digestive system used to tolerating and absorbing carbohydrates while you run. With practice, your stomach accepts food better during effort and your gut absorbs more energy per hour without discomfort.
How long does it take to train your gut?
Weeks, not days. It is best to start several weeks before your goal race, practice on your long runs and increase the amount of carbs gradually.
Why do gels upset my stomach when I run?
Because when you run your body diverts blood from your digestive system to your muscles and your gut processes food less well. If you give it a gel it isn’t used to, nausea or cramps follow. Training your gut greatly reduces this problem.
Should I only train my gut on easy runs?
No. You also need to practice at race pace, because that is when blood flow to the gut drops most and the discomfort appears.
Do all gels work the same?
No. Tolerance varies from person to person and from product to product. Try several brands, textures and formulas in training, stick with the one that suits you best and don’t change it on race day.
