Why Some Runners Struggle to Digest Gels During Races
Last update July 3, 2026 by Etienne Durocher
Few things are more frustrating than knowing exactly what you should do and still being unable to do it.
Many runners understand that fueling is important.
They know carbohydrates support performance.
They know energy gels can help maintain pace during long races.
They know underfueling often contributes to late-race fatigue.
And yet every time they take a gel, the same problem appears.
The stomach tightens.
Nausea develops.
The gut feels uncomfortable.
Sometimes the gel sits in the stomach like a brick.
Sometimes it triggers an urgent search for a portable toilet.
Sometimes it simply makes the runner swear they will never take another gel again.
The result is often a difficult choice.
Fuel and risk stomach problems.
Or avoid fueling and risk running out of energy later in the race.
Many runners assume they have a sensitive stomach.
Some conclude that gels simply do not work for them.
Others spend years searching for the perfect product while continuing to experience the same issues.
In reality, the problem is often much more complex.
And much more fixable.
One of the most encouraging discoveries in modern endurance nutrition is that many digestive issues are trainable. The stomach and intestines are not passive passengers during endurance events. Like muscles, they adapt to repeated stress.
Understanding why digestive problems occur is often the first step toward solving them.
For a complete approach to this topic, start with: Marathon Nutrition: Fueling Strategies for Race Day Success
What You Need to Know First
One of the biggest misconceptions in endurance sports is that energy gels are difficult to digest because they are somehow unnatural.
While certain products may work better than others for individual athletes, the reality is that most digestive issues stem from the interaction between exercise and digestion rather than from the gel itself.
Running creates a challenging environment for the digestive system.
When you exercise, blood flow is redirected toward working muscles, the cardiovascular system, and temperature regulation. The digestive tract receives less attention because digestion is not the body's immediate priority.
This creates an interesting situation.
The harder the effort becomes, the more difficult digestion can become.
At the exact moment runners need fuel the most, the body may become less efficient at processing it.
This is one reason stomach issues are much more common during races than during normal daily life.
You may tolerate a particular food perfectly well while sitting at home.
The same food consumed during a marathon may produce a completely different experience.
The digestive system is dealing with an entirely different set of circumstances.
Understanding this concept helps shift the conversation.
Instead of asking:
"Which gel should I buy?"
A better question is often:
"How can I help my digestive system perform more effectively under race conditions?"
That question usually leads to much better solutions.
For a broader overview of race fueling principles, Marathon Nutrition: Fueling Your Marathon provides the foundation behind many of the concepts discussed here.
The Problem Usually Starts Before Race Day
One of the most common patterns I see is runners expecting their stomach to perform tasks it has never practiced.
Imagine a runner who rarely consumes carbohydrates during training.
Most long runs are completed with little or no fuel.
Race day arrives.
Suddenly the athlete attempts to consume multiple gels, sports drinks, and carbohydrate sources over several hours.
The stomach receives more carbohydrate in a few hours than it typically receives during weeks of training.
When digestive issues appear, the runner blames the product.
In reality, the digestive system may simply be unprepared for the task.
This would be similar to entering a marathon without practicing long runs and then being surprised when the legs struggle after 30 kilometres.
The gut requires training just as the legs do.
Repeated exposure helps improve carbohydrate absorption, digestive comfort, and overall tolerance.
One of the core Philotimo nutrition principles is that fueling should be practiced throughout training.
Nothing new on race day.
The athletes who fuel best during races are rarely the athletes who discovered the perfect gel.
More often, they are the athletes who repeatedly practiced using their nutrition strategy during long runs.
Why One Runner Loves a Gel That Another Runner Hates
Another source of confusion is the enormous variation between athletes.
A gel that works perfectly for one runner may create significant discomfort for another.
This does not necessarily mean either athlete is doing something wrong.
Human digestion is highly individual.
Different athletes respond differently to:
carbohydrate concentrations
caffeine content
sweetness levels
texture
ingredients
fluid intake
This variability explains why nutrition advice often appears contradictory.
A runner may enthusiastically recommend a specific gel because it works perfectly for them.
Another runner may describe the exact same product as a disaster.
Both experiences can be true.
The objective is not to find the universally best gel.
The objective is to find the gel and fueling strategy that works best for your body.
This process requires experimentation.
It also requires patience.
Most successful fueling strategies are built through trial and refinement rather than instant success.
To go deeper into this aspect of training, read: How To Train Your Gut For Marathon And Ultramarathon Racing
The Most Common Causes of Race-Day Stomach Problems
One reason runners become frustrated with nutrition is that they assume digestive issues have a single cause.
More often, several factors contribute simultaneously.
A runner may start slightly too fast.
Hydration may be inconsistent.
Carbohydrate intake may be higher than what was practiced in training.
Race-day nerves may increase stress levels.
Weather conditions may be hotter than expected.
Individually, each factor may be manageable.
Together, they can create significant gastrointestinal distress.
This is one reason nutrition problems often seem unpredictable.
The gel itself may not have changed.
The environment surrounding it did.
Understanding these interactions helps runners move away from searching for one simple explanation and toward building a more complete strategy.
The Gel Is Often Not the Real Problem
One of the most valuable lessons runners can learn is that digestive discomfort is often blamed on the most obvious thing rather than the actual cause.
Insight
They struggle because their footwear is not aligned with their workload.
Guide Here
A runner takes a gel. Ten minutes later their stomach feels uncomfortable. The immediate conclusion is obvious: the gel caused the problem.
Sometimes that is true.
Many times it is not.
What runners often forget is that the digestive system is responding to everything happening during the race. Pace, hydration, temperature, anxiety, fatigue, caffeine intake, carbohydrate concentration, and previous nutrition decisions all influence how the stomach behaves. The gel may simply be the moment when an existing problem becomes noticeable.
I have worked with runners who switched brands repeatedly, searching for a magical solution. Gel after gel failed. Product after product seemed to cause issues. Yet when we reviewed the entire race, the underlying problem was often unrelated to the specific gel.
Sometimes they were starting too aggressively.
Sometimes they were underhydrated.
Sometimes they were attempting to consume far more carbohydrate than they had ever practiced in training.
The lesson is important because it changes the way solutions are approached. Instead of asking, "Which gel should I buy?" runners begin asking, "What is my digestive system trying to tell me?"
That question usually produces better answers.
The Relationship Between Hydration and Gel Absorption
One of the most overlooked aspects of race fueling is the relationship between carbohydrate intake and hydration.
Most energy gels are concentrated carbohydrate sources. They are designed to provide fuel efficiently, but they are not designed to replace fluid. When consumed without sufficient water, digestion may become more difficult.
This does not mean every gel requires large amounts of water immediately afterwards. Different products are formulated differently. However, runners who regularly consume gels without considering hydration often increase the likelihood of gastrointestinal discomfort.
Think of it this way.
Your digestive system is trying to process fuel while your body is simultaneously directing blood toward working muscles, cooling mechanisms, and cardiovascular demands. If fluid availability is reduced, the process becomes even more challenging.
This is one reason digestive issues often become more common later in races.
The athlete is more fatigued.
Hydration status may be declining.
Environmental stress may be increasing.
The gut is being asked to work under increasingly difficult circumstances.
A fueling strategy that worked perfectly at kilometre 10 may feel very different at kilometre 35.
Successful marathoners and ultramarathoners understand this relationship. They do not view fueling and hydration as separate systems. They understand that both must work together to support performance.
Caffeine: Helpful or Harmful?
Caffeine deserves special attention because it sits in an interesting category.
For many runners, caffeine is one of the most effective legal performance aids available. It can reduce perceived effort, improve alertness, and help athletes maintain focus during long events.
For others, it becomes part of the problem.
The challenge is that caffeine affects individuals differently. Some athletes tolerate high doses without issue. Others experience stomach discomfort, increased gastrointestinal urgency, or digestive irritation from relatively small amounts.
This is particularly important because many modern energy gels contain caffeine.
A runner may believe they are testing a new carbohydrate source when, in reality, they are also introducing a substantial amount of caffeine. When digestive issues occur, it becomes difficult to determine which factor played the larger role.
This is another reason race-day experimentation rarely ends well.
If caffeine is going to be part of the fueling strategy, it should be practiced repeatedly during long runs. Athletes should know how their body responds, how much works well, and whether there are any side effects.
Confidence comes from familiarity.
The more variables you eliminate before race day, the fewer surprises you are likely to encounter when the race begins.
Many runners believe they have a sensitive stomach when the real issue is simply lack of practice. If you'd like to understand how nutrition problems accumulate during longer events, I recommend reading Why Marathon Fueling Often Fails After 30K. It pairs naturally with the concepts discussed here.
Practical Strategies for Training Your Gut
The good news is that most digestive issues improve with practice.
The first step is consistency. If you only consume gels on race day, your stomach never has an opportunity to adapt. Long runs provide the perfect environment for practicing race nutrition under controlled conditions.
The second step is gradual progression. There is no need to immediately attempt the highest carbohydrate intake recommendations. Start with an amount that feels manageable and gradually increase as tolerance improves. Just as mileage increases progressively, carbohydrate intake often benefits from the same approach.
Third, simplify variables whenever possible. When testing a new gel, avoid simultaneously changing hydration, caffeine intake, breakfast, and pacing strategy. If everything changes at once, it becomes almost impossible to identify the true source of any problem.
Finally, keep notes. Athletes are often surprised by how much information they forget between training sessions. A simple record of products used, quantities consumed, weather conditions, and digestive response can reveal valuable patterns over time.
This naturally leads into: Electrolytes for Runners: When You Actually Need Them
A Coach's Perspective
One of the most encouraging things I tell athletes struggling with race nutrition is that they are usually not broken.
Many runners assume digestive discomfort means they have an unusually sensitive stomach or that they will never be able to fuel effectively during races. In reality, most successful endurance athletes have experienced some form of gastrointestinal challenge at some point in their development.
What often separates experienced runners from newer runners is not the absence of problems.
It is the willingness to systematically solve them.
I have seen athletes progress from being unable to tolerate a single gel during a long run to successfully fueling through marathons and ultramarathons. The transformation rarely happened because they discovered a miracle product. More often, it happened because they approached fueling with the same patience and consistency they applied to training.
This lesson appears repeatedly in endurance sports.
The body adapts.
The gut adapts.
Confidence adapts.
One coaching observation I have made over the years is that runners who treat nutrition as a skill tend to improve dramatically. The athletes who view fueling as a one-time decision often continue struggling.
The process matters.
Practice matters.
Patience matters.
Final Thoughts
Digestive issues during races are incredibly common.
They are also frequently misunderstood.
Many runners assume the gel itself is the problem when the reality is often far more complex. Hydration, pacing, carbohydrate intake, caffeine use, environmental conditions, and race-day stress all influence how the digestive system performs.
The encouraging news is that most of these factors can be improved.
Your stomach is not simply something you hope behaves on race day.
It is another system that can be trained.
The runners who fuel successfully during marathons and ultramarathons are rarely the athletes who found a perfect product on their first attempt. More often, they are the athletes who experimented, practiced, adjusted, and learned over time.
If there is one takeaway from this article, it is this:
Do not judge your fueling strategy based on a single bad experience.
Treat it like training.
Refine it.
Practice it.
Give it time to improve.
Because the ability to fuel comfortably during long races may be one of the most valuable endurance skills you ever develop.
If you'd like to continue improving your race-day nutrition strategy, the next logical step is reading How to Fuel Back-to-Back Long Runs for Ultramarathon Training, where we explore how repeated fueling challenges can strengthen both performance and digestive resilience.
