Energy Gels for Sensitive Stomachs
If energy gels upset your stomach, you're not alone.
Stomach cramps, bloating, nausea, an urgent need for the toilet or simply feeling that a gel is “sitting” heavily in your stomach can turn a good training session or race into a miserable one.
For runners, cyclists and triathletes with sensitive stomachs, the obvious conclusion is often:
“Energy gels just don't agree with me.”
But it may not be energy gels themselves that are the problem.
The type of carbohydrate, how concentrated your fuelling becomes in the stomach, how much carbohydrate you consume per hour, whether you're combining different carbohydrate sources, hydration, caffeine, exercise intensity and individual tolerance can all influence how comfortably you digest your race fuel.
And there is another important question that is becoming increasingly relevant:
Do you really need to consume extremely high amounts of carbohydrate every hour simply because modern sports nutrition says you can?
For athletes with sensitive stomachs, understanding the difference between fuel availability and fuel overload can make a significant difference.
This guide explains why energy gels can cause stomach problems, how maltodextrin differs from simple sugars, what multi-carb fuelling actually means, and how to develop a more comfortable fuelling strategy for running, cycling, triathlon and other endurance sports.
Why Do Energy Gels Upset Your Stomach?
An energy gel is essentially concentrated carbohydrate designed to provide readily available energy during exercise.
That sounds simple enough.
However, during harder exercise your digestive system is already operating under challenging conditions.
Your body prioritises blood flow to working muscles, while heat, dehydration, race intensity and nervousness can further influence digestion.
Then you introduce concentrated carbohydrate.
For some athletes, particularly those with sensitive stomachs, problems can begin when too much carbohydrate reaches the digestive system too quickly or when the overall concentration of fuel becomes difficult to process comfortably.
Common symptoms include:
- Stomach cramps
- Bloating
- Nausea
- A heavy or “sloshing” stomach
- Gas
- Diarrhoea or runner's tummy
- Feeling unable to eat or drink later in the event
That is why choosing an energy gel shouldn't simply be about finding the product with the largest carbohydrate number printed on the packet.
Digestibility matters too.
What Should You Look for in an Energy Gel for a Sensitive Stomach?
If you've previously experienced digestive problems with running gels, look beyond flavour and carbohydrate quantity.
Consider:
- The type of carbohydrate used
- Whether it contains simple sugars or longer-chain carbohydrates
- How concentrated your overall fuelling becomes
- Whether you're combining several carbohydrate sources
- How sweet the product is
- Whether it contains caffeine
- How many grams of carbohydrate you're consuming per hour
- How much water you're drinking
- What you ate before exercise
- The intensity at which you're exercising
One of the most important — and often overlooked — considerations is the carbohydrate source.
Simple Sugars vs Complex Carbohydrates
Not all carbohydrates used in sports nutrition are the same.
Simple sugars include carbohydrates such as:
- Glucose
- Fructose
- Sucrose
You'll find these, or ingredients containing them, in many sports drinks, chews and energy gels.
Maltodextrin is different.
It consists of multiple glucose units joined together and is classified as a complex carbohydrate.
Hammer Nutrition has long taken a different approach to endurance fuelling by using maltodextrin as the primary carbohydrate in Hammer Gel rather than adding simple sugars such as glucose, sucrose or fructose.
Why could that matter to an athlete with a sensitive stomach?
One answer involves something called osmolality.
What Is Osmolality — and Why Does It Matter?
Don't worry: we're not turning your Sunday long run into a chemistry degree.
But understanding this principle helps explain why some fuelling strategies sit comfortably while others can leave your stomach in open rebellion.
Osmolality relates to the concentration of dissolved particles in a solution.
Longer-chain carbohydrates such as maltodextrin can provide substantial amounts of carbohydrate while contributing fewer individual particles to a solution than the equivalent carbohydrate supplied as many smaller sugar molecules.
That can influence how concentrated the mixture in your digestive system becomes.
And during endurance exercise, your stomach rarely contains just one product.
Imagine taking:
Gel + sports drink + chews + another gel
Your stomach doesn't recognise four cleverly branded sports products.
It receives one combined nutritional mixture.
For athletes prone to GI problems, repeatedly increasing the carbohydrate concentration of that mixture may contribute to cramps, bloating, nausea or poor gastric emptying.
Why Maltodextrin Is Used in Endurance Fuel
Maltodextrin consists of longer chains of glucose molecules.
Because of its molecular structure, a maltodextrin-based fuel can provide substantial carbohydrate without requiring the same number of dissolved particles as an equivalent amount of carbohydrate made up entirely of shorter-chain sugars.
This is one reason maltodextrin has been used extensively in endurance sports nutrition.
Hammer Nutrition's approach is based on providing usable carbohydrate while avoiding unnecessary digestive overload.
Maltodextrin also has another practical advantage:
It isn't excessively sweet.
During a 30-minute workout this may not seem important.
During a six-, eight- or twelve-hour event it can become extremely important.
A flavour that tastes fantastic early in an event can become increasingly difficult to tolerate after hours of repeated consumption.
Less sweetness can therefore be a genuine advantage for prolonged endurance exercise.
But Isn't Maltodextrin High GI?
Yes.
And this is where sports nutrition is often misunderstood.
Maltodextrin has a high Glycaemic Index.
Normally, people hear “high GI” and assume that means it must be undesirable.
But context matters.
During prolonged or intense exercise, you're deliberately consuming carbohydrate because your muscles require readily available energy.
That is very different from consuming large quantities of high-GI processed carbohydrate while sedentary.
Hammer's philosophy is therefore not that all high-GI carbohydrate is bad.
It is that carbohydrate should be used intelligently and appropriately for the demands of exercise.
What Is Multi-Carb or Multiple-Transportable Carbohydrate Fuelling?
This is increasingly important for endurance athletes to understand.
You may have seen sports nutrition products advertising:
- Dual-source carbohydrate
- Multi-carb fuel
- Multiple transportable carbohydrates
- Glucose-fructose blends
- 90g carbohydrate per hour
- 100g carbohydrate per hour
- 120g carbohydrate per hour
The basic idea is legitimate.
Different carbohydrates can use different transport mechanisms in the intestine.
Glucose primarily uses one transport pathway, while fructose uses another.
By combining them, athletes attempting to consume very high quantities of carbohydrate can potentially absorb more carbohydrate than they could using glucose alone.
This is usually referred to as multiple transportable carbohydrate (MTC) fuelling.
For elite athletes competing at very high intensities and deliberately targeting extremely high carbohydrate availability, this can be a useful strategy.
But that does not mean it is automatically the best approach for every runner, cyclist or triathlete.
And it certainly doesn't mean:
“If 60 grams per hour is good, 120 grams must be twice as good.”
Your digestive system is rather more complicated than a petrol tank.
More Carbohydrate Isn't Automatically Better
Modern endurance nutrition increasingly promotes higher carbohydrate intake.
Typical discussions progress from:
30–60g per hour
to:
60–90g per hour
and increasingly:
90–120g+ per hour.
The theory is straightforward:
More carbohydrate available = more carbohydrate available for energy.
But the question athletes with sensitive stomachs should ask is slightly different:
How much carbohydrate can I actually consume, digest and use comfortably at my race intensity?
These are not necessarily the same number.
There is an important distinction between:
maximum carbohydrate absorption
and
optimal individual fuelling.
Hammer Nutrition's philosophy has traditionally resisted the assumption that maximum intake automatically equals maximum performance.
Instead, Hammer advocates supplying the body with enough fuel to support performance without unnecessarily overwhelming digestion.
This is the foundation of Hammer's:
Less is Best
fuelling philosophy.
Multi-Carb Fuelling May Increase Absorption — But You Still Have to Tolerate It
Multiple transportable carbohydrates can help athletes absorb high carbohydrate intakes.
That doesn't make the digestive system limitless.
The athlete still has to tolerate:
- The total carbohydrate quantity
- Fructose
- Fluid volume
- Product concentration
- Exercise intensity
- Heat
- Caffeine
- Pre-race food
- Repeated feeding over many hours
Some athletes can comfortably tolerate very high carbohydrate intakes.
Others cannot.
And an athlete repeatedly suffering from bloating, nausea, diarrhoea or stomach cramps probably shouldn't assume that the answer is simply to train themselves to consume even more carbohydrate.
First determine whether the existing strategy is already exceeding what your digestive system comfortably handles.
What Does “Gut Training” Mean?
You'll increasingly hear athletes being advised to train the gut.
There is genuine evidence that repeated exposure to carbohydrate during training can improve tolerance and carbohydrate absorption.
That makes sense.
You should practise your race nutrition during training rather than introducing large amounts of fuel for the first time on race day.
But there's an important distinction between:
training your digestive system to handle appropriate race nutrition
and
forcing ever-increasing amounts of carbohydrate simply to reach an arbitrary grams-per-hour target.
Your target should ultimately be determined by:
- Event duration
- Intensity
- Body size
- Fitness
- Metabolic characteristics
- Environmental conditions
- Your overall diet
- Your individual digestive tolerance
Not because somebody on social media says every endurance athlete now needs 120g per hour.
Your Body Already Carries Energy
Your body doesn't start an endurance event with an empty fuel tank.
You have stored carbohydrate in the form of glycogen in your muscles and liver.
You also possess a much larger store of energy in the form of body fat.
The challenge during endurance exercise isn't simply to replace every calorie being burned with carbohydrate.
That would often be neither practical nor necessary.
The body uses a mixture of fuels, with the proportion of carbohydrate and fat changing according to exercise intensity, fitness, training status and individual metabolism.
That is one reason Hammer's strategy has historically focused on supplementing the body's existing energy stores rather than trying to replace every calorie expended.
Why Sensitive-Stomach Athletes Should Pay Particular Attention to High-Carb Fuelling
If you can comfortably consume a high-carbohydrate strategy and it improves your performance, that's valuable information.
But if you're reading this page because:
“Energy gels keep upsetting my stomach”
then aggressively increasing carbohydrate intake may be the wrong place to start.
Instead, ask:
What am I actually consuming each hour?
Many athletes dramatically underestimate their total carbohydrate intake because they count each product separately.
For example:
- 2 energy gels
- Carbohydrate sports drink
- Energy chews
- Banana
- Sweets from an aid station
- Cola later in the race
could add up to far more carbohydrate than you intended.
Before changing brands, calculate the whole strategy.
One Stomach, Not Five Separate Products
This is perhaps the simplest lesson on this page.
Your stomach doesn't care that your nutrition comes from:
- Brand A gel
- Brand B drink
- Brand C chew
- Aid-station cola
- Half a banana
It all arrives in one digestive system.
Athletes frequently blame the final gel they consumed because that's when symptoms appeared.
The real cause may have been the cumulative carbohydrate load over the previous two hours.
That is why Hammer generally favours keeping endurance nutrition as simple and controllable as possible.
Don't Wash a Concentrated Gel Down With a High-Carbohydrate Drink Without Thinking
This is especially important.
Taking a gel and immediately washing it down with a carbohydrate-heavy sports drink adds even more carbohydrate to the mixture entering your digestive system.
That doesn't automatically mean you'll experience stomach trouble.
Many athletes deliberately combine carbohydrate sources successfully.
But if you're already struggling with GI distress, simplify your strategy.
A practical approach is to clearly understand which product is doing which job.
For example:
Fuel provides calories.
Water provides hydration.
Electrolytes replace electrolytes.
Some products perform more than one function — but you should know where every gram of carbohydrate is coming from.
Can Maltodextrin Be Easier on the Stomach?
For many athletes, maltodextrin-based fuelling can provide an alternative to products relying heavily on simple sugars.
Its longer carbohydrate chains allow substantial carbohydrate delivery without creating the same number of dissolved particles as an equivalent amount of shorter-chain simple sugars.
That is one reason maltodextrin is widely used in endurance nutrition.
It does not mean maltodextrin guarantees freedom from stomach problems.
No responsible sports nutrition company should make that promise.
Individual tolerance varies, and gastrointestinal symptoms can also result from:
- Overconsumption
- Dehydration
- Heat
- High exercise intensity
- Caffeine
- Pre-race meals
- Underlying gastrointestinal conditions
Carbohydrate choice is one important part of the equation — not the entire equation.
Why Hammer Gel Takes a Different Approach
Hammer Gel uses maltodextrin as its primary carbohydrate source rather than relying on added simple sugars such as glucose, sucrose or fructose.
The approach is deliberately simple.
Hammer Gel provides:
- Maltodextrin-based complex carbohydrate
- No added simple sugars
- A less excessively sweet taste
- A concentrated and portable endurance fuel
- Caffeinated and non-caffeinated options
- Flexible use for running, cycling, triathlon and endurance sport
For athletes who struggle with very sweet or high-simple-sugar gels, it offers a different approach worth testing.
Why “No Added Fructose” May Interest Some Athletes
Fructose is commonly included in modern multiple-carbohydrate fuelling systems because it uses a different intestinal transporter from glucose.
That can help increase total carbohydrate absorption at high intakes.
However, fructose tolerance varies significantly between individuals.
Some athletes tolerate it extremely well.
Others find larger amounts contribute to:
- Bloating
- Gas
- Cramping
- Loose stools
That does not make fructose inherently “bad”.
But if you're experiencing repeated stomach problems with multi-carb glucose/fructose gels, testing a different carbohydrate strategy may help identify whether the formulation, total quantity or both are contributing.
Hammer Gel does not rely on added fructose as a carbohydrate source.
Caffeine Can Also Affect a Sensitive Stomach
Carbohydrate isn't the only ingredient worth checking.
Many energy gels contain caffeine.
Caffeine can support alertness and endurance performance, but some athletes tolerate it far better than others.
If caffeine affects your stomach, don't discover this during a marathon.
Use non-caffeinated gels for the majority of your fuelling and introduce caffeine strategically only if you've tested it successfully during training.
Hammer Gel includes both caffeinated and non-caffeinated flavour options, allowing you to control caffeine intake instead of consuming caffeine in every serving.
Water Still Matters
A perfectly chosen gel can still cause problems if your hydration strategy is poor.
Dehydration itself can contribute to gastrointestinal distress.
Taking concentrated carbohydrate while becoming progressively dehydrated can therefore create exactly the conditions you're trying to avoid.
Rather than swallowing several gels and then waiting until you're desperately thirsty, drink according to conditions, intensity and your individual requirements.
The correct amount varies enormously depending on:
- Temperature
- Humidity
- Sweat rate
- Body size
- Exercise intensity
- Event duration
Avoid blindly following an enormous fixed water target as well.
As with carbohydrate:
More is not automatically better.
Don't Try a New Energy Gel on Race Day
One of the most effective sensitive-stomach strategies costs absolutely nothing.
Practise.
Never make race morning the first time you try a new gel or a new 90g-per-hour fuelling strategy.
Your longer training sessions are rehearsals for your nutrition strategy as much as they are for your muscles.
Test:
- Which carbohydrate sources you tolerate
- How frequently you need fuel
- How much carbohydrate you tolerate
- Water intake
- Caffeine
- Electrolytes
- Exercise intensity
- Hot-weather conditions
Once you've found a strategy that works, resist the temptation to completely reinvent it because someone at race registration tells you what the professionals are doing.
Their digestive system isn't yours.
Start With What You Need — Not the Maximum You Can Swallow
If you've previously struggled with gels, don't immediately jump into an aggressive fuelling schedule.
Start conservatively during training.
Monitor:
- Energy levels
- Stomach comfort
- Performance
- Hunger
- Hydration
- Recovery
Then adjust gradually.
This gives you useful information.
Blindly jumping from 50g to 100g carbohydrate per hour and hoping your stomach eventually learns to cope tells you considerably less.
Your ideal intake depends on the athlete and the event.
There is no magic number that every runner, cyclist and triathlete must consume.
Give Your Pre-Race Meal Time to Digest
Sometimes the gel gets blamed for a stomach that was already overloaded before the starting gun.
Eating a large meal shortly before intense exercise means your digestive system may still be processing that food when your muscles begin demanding increasing blood flow.
Hammer Nutrition generally recommends allowing approximately three hours between your main pre-event meal and the start.
Keep that meal familiar.
Race morning isn't the time for a heroic hotel breakfast because you've convinced yourself you'll “burn it off anyway”.
Your stomach may have other ideas.
A Simple Sensitive-Stomach Fuelling Strategy
If you've lost confidence in energy gels, simplify the experiment.
Before training
Eat a familiar pre-exercise meal with sufficient time to digest.
Avoid unusual foods.
During training
Choose one primary carbohydrate approach.
Know approximately how much carbohydrate you're consuming.
Take gels with water.
Start conservatively.
Don't automatically add sugary drinks, chews and sweets on top.
After training
Write down:
- What you consumed
- How much
- When
- Fluid intake
- Weather
- Intensity
- Any stomach symptoms
Patterns often become obvious surprisingly quickly.
Sensitive-Stomach Marathon Fuelling
The marathon is one of the worst places to discover a nutrition problem.
Digestive issues frequently don't appear immediately.
They accumulate.
Practise your entire strategy during long runs:
- Breakfast
- Pre-start timing
- Gel choice
- Carbohydrate intake
- Water intake
- Electrolytes
- Caffeine
Most importantly, practise it at an intensity resembling your intended marathon effort.
Something that sits perfectly comfortably during an easy Sunday run may behave very differently at marathon pace.
Read our complete Hammer Gel Fuelling Guide for more guidance on timing and race-day use.
Sensitive-Stomach Fuelling for Cycling and Triathlon
Cyclists and triathletes face another challenge:
duration.
Over a long event there are many opportunities for small fuelling errors to accumulate.
A slightly excessive carbohydrate intake every hour can become a very different digestive situation six hours later.
Think about nutrition across the entire event rather than treating every hour in isolation.
For longer endurance events, gels may form only one part of a broader fuelling strategy.
Hammer's Perpetuem is specifically designed for prolonged endurance exercise when athletes want an alternative to surviving the entire day on gels and sugar.
If Every Gel Upsets Your Stomach, Look at the Whole Strategy
If you've tried several brands and still experience stomach problems, another brand may not be the answer.
Ask yourself:
How many grams of carbohydrate am I really consuming per hour?
Am I combining glucose/fructose multi-carb gels with carbohydrate drinks and chews?
Am I drinking enough water?
Am I dehydrated before I begin?
Am I eating too close to the start?
Am I consuming excessive caffeine?
Does the problem only occur at high intensity?
Have I actually practised this strategy repeatedly?
Sometimes the solution isn't another gel.
It's a better fuelling strategy.
Persistent or severe gastrointestinal symptoms should be discussed with an appropriately qualified healthcare professional rather than simply being attributed to sports nutrition.
Frequently Asked Questions
What are the best energy gels for sensitive stomachs?
No energy gel is guaranteed to suit every athlete.
Look at carbohydrate type, sweetness, caffeine, total carbohydrate intake and how you're using the product.
Athletes struggling with heavily simple-sugar-based or glucose/fructose gels may wish to test a maltodextrin-based alternative such as Hammer Gel during training.
Why do energy gels make my stomach hurt?
Possible causes include excessive carbohydrate intake, highly concentrated fuelling, insufficient water, dehydration, caffeine sensitivity, eating too close to exercise, high intensity and individual sensitivity to particular carbohydrate sources.
The gel packet itself may therefore be only one part of the problem.
What are multi-carb energy gels?
Multi-carb or multiple-transportable-carbohydrate gels generally combine carbohydrates such as glucose and fructose.
Because these carbohydrates use different transport pathways in the intestine, combining them can increase total carbohydrate absorption, particularly when athletes are attempting very high carbohydrate intakes.
That can be useful for some athletes but doesn't mean every endurance athlete needs to pursue maximum carbohydrate intake.
Are multi-carb gels better?
Not automatically.
They can be advantageous for athletes deliberately targeting high carbohydrate intake and who tolerate them well.
The best strategy is the one that provides sufficient energy while remaining comfortable and sustainable at your event intensity.
For an athlete experiencing repeated GI distress, increasing carbohydrate intake simply because more can theoretically be absorbed may be counterproductive.
Do I need 90–120g of carbohydrate per hour?
Not every athlete does.
Carbohydrate requirements vary according to event duration, intensity, body size, fitness, diet and individual tolerance.
Higher carbohydrate strategies can work extremely well for some athletes.
Others perform comfortably on less.
Don't confuse a maximum potential intake with a universal requirement.
What does “train your gut” mean?
Gut training involves practising carbohydrate consumption during training so your digestive system becomes accustomed to your race-day nutrition strategy.
This can improve tolerance.
However, the goal should be to develop a fuelling strategy appropriate to you — not simply force your body to tolerate ever-increasing quantities of carbohydrate.
Are maltodextrin energy gels easier to digest?
Maltodextrin consists of longer carbohydrate chains and can deliver substantial carbohydrate while contributing fewer dissolved particles than an equivalent amount of shorter-chain simple sugars.
This is one reason it has traditionally been popular in endurance nutrition.
Individual tolerance still varies.
Does Hammer Gel contain simple sugars?
Hammer Gel uses maltodextrin as its primary carbohydrate source and does not add simple sugars such as glucose, sucrose or fructose.
Does Hammer Gel contain fructose?
Hammer Gel does not rely on added fructose as a carbohydrate source.
Athletes who suspect glucose/fructose gels contribute to their stomach problems may therefore find it useful to test a different carbohydrate approach during training.
Is Hammer Gel suitable for sensitive stomachs?
Hammer Gel's maltodextrin-based and mildly sweet formulation makes it an option worth testing for athletes who struggle with conventional gels.
However, no gel can guarantee freedom from gastrointestinal problems.
Total carbohydrate intake, hydration, caffeine, intensity and individual tolerance remain important.
Should I take energy gels with water?
Generally, yes.
Water helps dilute concentrated carbohydrate after it enters the stomach while contributing to hydration.
Be cautious about automatically washing every gel down with a high-carbohydrate sports drink if you haven't calculated the combined carbohydrate load.
Can too many energy gels cause diarrhoea?
Excessive carbohydrate intake, dehydration, exercise intensity and individual intolerance can all contribute to gastrointestinal symptoms including diarrhoea.
Look at your total hourly carbohydrate intake, not simply the number of gels consumed.
Can energy gels cause runner's tummy?
Energy gels can contribute, particularly if the overall fuelling strategy exceeds your digestive tolerance.
Runner's tummy can also be affected by exercise intensity, hydration, caffeine, pre-race food and individual GI sensitivity.
Should I avoid fructose if I have a sensitive stomach?
Not necessarily.
Many athletes tolerate fructose very well and glucose/fructose combinations can increase carbohydrate absorption.
Others experience GI symptoms when consuming larger quantities.
The correct approach is to test your nutrition during training and determine your own tolerance.
How can I train my stomach for energy gels?
Practise your intended fuelling strategy during long training sessions.
Start with an amount you tolerate comfortably and adjust gradually according to energy requirements and performance.
Train your nutrition strategy just as deliberately as you train your pacing.
The Best Fuelling Strategy Is the One You Can Actually Use
Endurance nutrition shouldn't be a competition to see who can consume the greatest number of carbohydrate grams per hour.
Nor should athletes be frightened of carbohydrate.
Carbohydrate is an extremely useful endurance fuel.
The important questions are:
What type?
How much?
When?
And can your digestive system comfortably handle it?
Multi-carb glucose/fructose strategies can allow very high carbohydrate absorption and may work extremely well for athletes who require and tolerate that approach.
But athletes with sensitive stomachs shouldn't assume that increasing carbohydrate intake is automatically the solution.
Sometimes simplifying the strategy produces the better result.
Hammer Nutrition has spent decades advocating a deliberately measured approach:
Less is Best.
Provide your body with enough fuel to support performance without unnecessarily overwhelming your digestive system.
Hammer Gel follows this philosophy with a maltodextrin-based complex carbohydrate formula, no added simple sugars and a less excessively sweet taste designed for prolonged endurance use.
Most importantly:
Test your nutrition in training. Understand what you're consuming. Find the amount your body can comfortably use. Then stick to what works on race day.
Read the Hammer Gel Fuelling Guide →
Further Reading
Complex Carbohydrates: High GI vs Low GI & Simple Sugars →
Maltodextrin: The Superior Carbohydrate for Endurance Athletes →
