The Science Behind Why Running Gels Can Upset Your Stomach
Experiencing stomach issues mid-run is frustrating and can severely impact performance. Several physiological and nutritional factors combine during intense exercise to increase the risk of gastrointestinal (GI) distress when consuming running gels.
Reduced Blood Flow During Exercise
During intense physical activity like running, your body prioritizes blood flow to the working muscles in your arms and legs. This redirection of blood means that less is sent to the digestive system, slowing down digestion and absorption. What the gut would normally process with ease in a resting state becomes a challenge when you're pushing your limits. This reduced digestive efficiency is a primary reason why concentrated carbohydrates from gels can sit heavy and cause issues.
The High Concentration of Sugars
Most traditional energy gels are a concentrated formula of carbohydrates, primarily simple sugars like glucose, maltodextrin, and fructose. While this is designed for rapid energy delivery, it can overwhelm the digestive system. The body reacts to the high sugar concentration by pulling water from the bloodstream into the stomach and intestines to dilute the solution. This can lead to a host of problems, including bloating, cramping, and diarrhea, especially if not consumed with sufficient water.
Osmotic Effect and Dehydration
The high concentration (osmolality) of a gel is a major culprit. When you don't consume enough water alongside a non-isotonic gel, the gel pulls water from your body into your gut for digestion. This can lead to dehydration and further exacerbate GI symptoms. Maintaining a proper fluid balance is critical, as dehydration alone can significantly delay gastric emptying and increase the likelihood of stomach upset.
Ingredient Sensitivity and FODMAPs
The specific carbohydrate sources in a gel can also play a role. Some gels rely heavily on fructose, a type of sugar that uses a different intestinal transporter than glucose. The transporter for fructose (GLUT5) has a lower capacity, and when large amounts of fructose are consumed, it can lead to malabsorption and fermentation in the large intestine. This can cause gas, bloating, and other GI symptoms, especially for athletes with sensitivities like IBS. This concept is related to the FODMAP diet, which aims to reduce poorly absorbed carbohydrates.
Nerves and Stress
Pre-race anxiety is known to affect the GI system. Stress and nerves can trigger your fight-or-flight response, further impacting the gut's ability to function normally. This can make an athlete more susceptible to GI issues from a gel they would normally tolerate during a training run. Practice, familiarity, and a good race-day strategy can help mitigate this.
Comparison Table: Types of Energy Gels
| Type of Gel | Water Requirement | Primary Carbohydrates | Common Ingredients | Best For |
|---|---|---|---|---|
| Classic Gels | Requires water to aid digestion. | Maltodextrin, Fructose, Glucose. | Sugars, water, electrolytes, flavors, preservatives. | Standard use on training runs and races. |
| Isotonic Gels | No extra water required; pre-hydrated. | Maltodextrin (with specific ratios). | Maltodextrin, water, electrolytes. | Hot weather, hydration focus, sensitive stomachs. |
| Natural Gels | Varies, often with water. | Fruit purees, rice syrup, honey. | Fruit, syrup, sea salt, electrolytes. | Sensitive stomachs, cleaner fuel source. |
| Caffeinated Gels | Requires water (for non-isotonic versions). | Maltodextrin, Fructose, Glucose, Caffeine. | Sugars, water, caffeine, electrolytes. | Late stages of a race for a mental lift. |
| Hydrogels | No extra water required; encapsulated carbs. | Glucose, Fructose (specific ratios). | Maltodextrin, water, pectins, and alginates. | High-carb fueling needs, sensitive guts. |
Practical Ways to Prevent Stomach Upset from Gels
Preventing GI issues involves more than just choosing a different gel. It requires a holistic approach that includes gut training, proper hydration, and smart race-day strategy.
Train Your Gut
Your digestive system can be trained to tolerate carbohydrates during exercise, just like your muscles are trained for endurance. By regularly consuming gels (or other carbs) during your long training runs, you teach your gut to absorb fuel more efficiently under race-day conditions. This helps your body adapt and reduces the risk of surprising it with a concentrated carbohydrate load on race day. Consistent training at your intended race pace while consuming gels is key.
Prioritize Proper Hydration
Always consume gels with water. For traditional, non-isotonic gels, this is non-negotiable, as the water is needed to help dilute and absorb the concentrated sugars. Even with isotonic or hydrogels, maintaining overall hydration is crucial, as dehydration significantly increases the chances of GI problems. Make a plan for when and where you will take on water during your race and practice this during training.
Choose the Right Gel for You
Not all gels are created equal, and individual tolerance varies greatly. Experiment with different brands, carb blends (e.g., glucose-fructose mixes), and textures during your training runs. If you have a sensitive stomach, consider isotonic or natural gels. Check the ingredients for specific potential irritants like excessive fructose or high amounts of magnesium, which has a laxative effect. A mix of carbohydrate types can also be more tolerable than a single source.
Time Your Fueling Strategy
Timing is everything. For long-distance running, aim to consume gels at regular intervals, typically every 45-60 minutes, rather than all at once. For runs over 90 minutes, start fueling earlier, before your glycogen stores are fully depleted. Also, avoid taking gels or heavy meals too close to the start of your run, which can lead to a crash.
Other Mitigation Strategies
- Avoid NSAIDs: Over-the-counter anti-inflammatory drugs like ibuprofen can increase gut permeability and worsen GI issues. It's best to avoid them before and during races. Springer Link
- Consider a Low-FODMAP Approach: Some athletes find success by temporarily limiting high-FODMAP foods, including some fruits high in fructose, in the days leading up to a race.
- Manage Stress: Develop pre-race rituals that help reduce anxiety, as this can calm the gut.
Conclusion
Yes, running gels can and do upset some people's stomachs, but it is not an inevitable outcome. GI distress is often a product of a complex interplay between reduced blood flow, high sugar concentrations, dehydration, and individual sensitivities. By understanding these factors and implementing a strategic approach—including training your gut, optimizing hydration, and experimenting with different gel types—you can minimize the risk of stomach issues. The golden rule remains: never try anything new on race day. Practice your fueling strategy repeatedly in training to ensure a confident and comfortable race-day performance.
