The Science Behind Why Gels Can Cause GI Distress
For many endurance athletes, energy gels are a convenient way to get quick fuel during long sessions. However, it's not uncommon for them to cause digestive issues. Understanding the science behind these problems is the first step toward preventing them. The primary cause of stomach discomfort during exercise is that your body redirects blood flow away from your digestive system and towards your working muscles. This compromises your gut's ability to digest food and absorb nutrients effectively. When a highly concentrated dose of carbohydrates from a gel enters this compromised system, it can trigger a range of unpleasant symptoms.
Reduced Blood Flow to the Gut
During high-intensity exercise, your body prioritizes sending oxygen-rich blood to your extremities to power your movements. This happens at the expense of blood flow to your gastrointestinal tract. With reduced blood supply, the gut's normal functions slow down, making it more vulnerable to irritation from highly concentrated substances like energy gels. This effect is amplified during intense races compared to easier training runs.
Osmotic Stress and Concentration
A key factor in gel-induced GI issues is osmolality—the concentration of solutes in a solution. Most traditional energy gels are hypertonic, meaning they have a higher solute concentration than your body's fluids. When you consume a hypertonic gel without sufficient water, your body pulls water from your cells and bloodstream into your intestine to dilute the sugar concentration. This process can lead to bloating, cramping, and even diarrhea. It also contributes to dehydration, further impacting performance.
The Role of Carbohydrate Ratios
Not all carbohydrates are absorbed the same way. The body uses different transporters for glucose (including maltodextrin) and fructose. The transporter for glucose (SGLT1) can become saturated at around 60 grams per hour. If a gel contains only glucose and you consume more than this amount, the excess unabsorbed carbohydrates sit in the gut, fermenting and causing problems like gas and bloating. To combat this, many newer gels use a dual-carbohydrate strategy, combining glucose and fructose in a specific ratio (often 2:1 or 1:0.8). This allows your body to absorb up to 90 grams or more of carbohydrates per hour by using both transport pathways simultaneously, which can significantly reduce the risk of GI upset.
Problematic Ingredients
Beyond just carbohydrates, other ingredients in energy gels can contribute to stomach distress. Artificial sweeteners, preservatives, and coloring agents are difficult for some people to digest, potentially irritating the gut. Some gels also contain high levels of magnesium, which is a known laxative when consumed in large quantities. Caffeine is another ingredient that increases gut motility and can be problematic for those with sensitive stomachs, especially during intense exercise.
Types of Energy Gels: A Comparison
Choosing the right gel for your body is crucial. The following table compares traditional (hypertonic) gels with the newer isotonic and hydrogel varieties.
| Feature | Traditional Gels (Hypertonic) | Isotonic Gels / Hydrogels |
|---|---|---|
| Composition | Concentrated syrup; high sugar content. | Pre-mixed with water; lower sugar concentration. |
| Water Requirement | Must be consumed with ample water to aid digestion. | Can be consumed without extra water for absorption. |
| Absorption Rate | Slower absorption if not consumed with enough water. | Faster absorption due to balanced concentration. |
| GI Comfort | Higher risk of bloating, cramping, and stomach upset. | Lower risk of digestive issues, gentler on the stomach. |
| Convenience | Smaller packet size, requires carrying extra water. | Larger, often bulkier packet, self-contained hydration. |
| Best For | Athletes who prefer a small packet and can consistently take water with it. | Athletes with sensitive stomachs or those who need a quicker, more convenient option. |
How to Prevent and Manage Energy Gel Stomach Issues
If you've experienced GI issues with gels, don't give up on them completely. Several strategies can help you find a fueling approach that works for you. The key is to experiment and find what your body tolerates best.
- Stay Hydrated: This is arguably the most important tip. Always consume water with a traditional, concentrated gel to help your body absorb it properly. Dehydration makes all GI symptoms worse.
- Choose the Right Carb Ratio: Opt for gels containing a mix of glucose/maltodextrin and fructose, especially if you aim for a high carbohydrate intake per hour. This dual-carbohydrate approach utilizes different intestinal transporters for more efficient absorption.
- Try Isotonic or Hydrogels: For those with highly sensitive stomachs, isotonic gels or newer hydrogel formulas (e.g., Maurten) are designed to be absorbed more easily and may prevent distress.
- Avoid Problematic Ingredients: If you suspect a specific component is causing issues, try switching to gels with simpler, more natural ingredients. Also, be mindful of caffeine, as it can be a gut irritant for some.
- Fueling Strategy: Instead of taking one large gel at once, try consuming smaller amounts more frequently. This spreads the carbohydrate load over time, making it easier for your gut to handle. Consider a strategy like a quarter-gel every 10-15 minutes.
- Experiment in Training: The golden rule of sports nutrition is to never try anything new on race day. Use your long training sessions to test different gel brands, flavors, and intake strategies. This allows your body to adapt.
- Avoid High-Fiber Foods Pre-Race: In the days leading up to a race, consider reducing your intake of high-fiber foods. Fiber can increase the risk of bowel movements during exercise and cause unnecessary gas.
- Train Your Gut: Your digestive system is trainable, just like your muscles. By regularly consuming carbohydrates during training, you can increase your body's capacity to absorb fuel during exercise.
Conclusion: The Final Word on Gels and Your Stomach
Ultimately, the question, do energy gels upset the stomach, has a conditional answer. Yes, they can—but they don't have to. For most athletes, GI problems result from a combination of concentrated carbohydrates, inadequate hydration, and the physiological stress of exercise. By understanding these root causes, choosing the right type of gel for your needs, and, most importantly, practicing your fueling strategy during training, you can mitigate and often eliminate stomach issues. Your digestive system is a critical part of your performance engine, and with consistent training and smart choices, you can make it as resilient as the rest of your body. For further reading, Dr. Asker Jeukendrup is a prominent sports nutrition scientist who has done extensive research in this area, including on gut training techniques. Learn more about training your gut for optimal performance here.
