The Importance of Carbohydrates for Endurance Performance
For endurance athletes, carbohydrates are the body's primary and preferred fuel source, especially during prolonged or high-intensity exercise. These are broken down into glucose, which is stored as glycogen in the liver and muscles. During an event, this stored glycogen is converted back into glucose to provide energy. However, muscle and liver glycogen stores are limited and can be depleted within 60–90 minutes of continuous, high-effort activity. When these stores run low, athletes experience a rapid drop in energy, often called 'hitting the wall.' Therefore, consuming carbohydrates during the event is crucial to maintain blood glucose levels, spare glycogen stores, and sustain performance.
The Science Behind Combining Sugars
Recent sports nutrition research has moved beyond the idea of fueling with a single type of sugar, like glucose, exclusively. The intestinal lining can only absorb about 60 grams of glucose per hour through a specific transporter called SGLT1. For athletes with higher energy demands, such as those in ultra-endurance events, consuming more than this amount can lead to gastrointestinal distress.
The solution is to use multiple transportable carbohydrates. Fructose, a simple sugar found in fruits and honey, uses a different transporter (GLUT5) for absorption. By combining glucose and fructose, athletes can increase their total carbohydrate absorption to 90–120 grams per hour or more, utilizing separate pathways and minimizing GI issues.
Optimal Glucose-Fructose Ratios:
- 2:1 Ratio: Historically recommended for intakes up to 90 g/h, offering a balance of availability and comfort.
- 1:0.8 Ratio: Newer research shows this ratio is even more effective for maximizing absorption and oxidation, especially at very high intake rates (90–120 g/h), and is used in many modern sports nutrition products.
Comparing Different Sugar Sources for Athletes
| Sugar Source | Type | Absorption Speed | Best Use Case | Key Benefit for Athletes |
|---|---|---|---|---|
| Maltodextrin | Complex (chains of glucose) | Fast | During-event fueling & post-exercise recovery. | High-GI, rapid energy without excessive sweetness. |
| Dextrose (Glucose) | Simple (monosaccharide) | Very Fast | Quick energy boost during intense, short efforts. | Immediate energy source for working muscles and brain. |
| Fructose | Simple (monosaccharide) | Slower than glucose | Paired with glucose to increase total carb absorption. | Utilizes a separate intestinal transporter, enhancing overall uptake. |
| Sucrose (Table Sugar) | Simple (glucose + fructose) | Fast | General fueling and convenient energy source. | Naturally provides both glucose and fructose in a 1:1 ratio. |
A Strategically Timed Fueling Approach
For endurance events, fueling is a multi-stage process that leverages different carbohydrate types at different times.
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Before the Event (Carb-Loading): In the 36–48 hours leading up to a long event, athletes should increase carbohydrate intake to maximize muscle and liver glycogen stores. Focus on low-fiber, complex carbs like white pasta, rice, and potatoes to avoid stomach upset. For example, aim for 10-12 grams of carbohydrates per kilogram of body weight per day.
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During the Event: This is where simple and fast-absorbing sugars shine. The goal is to provide a continuous supply of energy. For efforts over 90 minutes, start consuming 30–60 grams of carbohydrates per hour within the first hour. For longer efforts (2.5+ hours), increase intake to 60–120 grams per hour using a glucose-fructose blend. Energy gels, chews, and sports drinks containing maltodextrin and fructose are excellent choices.
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After the Event (Recovery): The post-exercise window is critical for muscle glycogen replenishment and repair. Consuming a combination of simple carbohydrates (like dextrose) and protein within an hour of finishing can significantly accelerate recovery. This helps transport nutrients back into the muscle cells and prepares the body for the next training session.
The Rise of Hydrogels and Highly Branched Cyclic Dextrin
Advanced sports nutrition has led to innovative fueling formats like hydrogels and products featuring Highly Branched Cyclic Dextrin (HBCD), also known as Cluster Dextrin. Hydrogels combine carbohydrate with a gelling agent to create a semi-solid substance that can be more gentle on the stomach and allow for higher carb intake. HBCD is a highly soluble carbohydrate with a low osmolality, meaning it passes through the stomach faster than traditional glucose or maltodextrin, reducing the risk of GI issues and providing a sustained energy release. These products are particularly useful for athletes with sensitive stomachs or for ultra-endurance events where high-volume carb intake is necessary.
The Verdict: A Combination is Key
There is no single "best type of sugar for endurance athletes"; rather, the most effective strategy involves using a combination of fast-absorbing and multi-transportable carbohydrates. For most athletes, a blend of maltodextrin and fructose in a scientifically-backed ratio (like 1:0.8) during the event provides the optimal balance of rapid energy delivery, high absorption rates, and minimal digestive stress. Timing is equally important, with different carbohydrate sources and quantities needed before, during, and after exercise to maximize performance and recovery. Training the gut to tolerate higher carbohydrate intake is also a crucial step for athletes to reach their full potential. For further evidence on the effectiveness of dual-carbohydrate fueling, see the study on multiple transportable carbohydrates.
Frequently Asked Questions
Is dextrose or maltodextrin better for athletes?
Maltodextrin is generally superior during endurance events because its longer glucose chains provide sustained energy without being overly sweet, and its lower osmolality aids digestion. Dextrose, being pure glucose, is excellent for rapid absorption post-workout but can be too sweet and cause GI issues in large volumes during exercise.
What are the best foods for getting sugar before a race?
For a pre-race meal, focus on low-fiber, high-carbohydrate options like white rice, white bread, and low-fat pancakes. Whole fruits like bananas are also a great choice for a quick, digestible energy source.
Should I mix different sugars in my sports drink?
Yes, mixing different sugars like maltodextrin (glucose) and fructose allows for higher total carbohydrate absorption per hour by utilizing different intestinal transporters. This strategy provides more energy and reduces the risk of gastrointestinal problems.
How much sugar should an athlete consume per hour during an ultra-event?
For events lasting over 2.5 hours, current guidelines recommend consuming 90–120 grams of carbohydrates per hour, preferably from a glucose and fructose blend. This high intake requires specific 'gut training' to be tolerated effectively.
Is sucrose (table sugar) bad for endurance athletes?
No, sucrose is not bad for athletes when used strategically. It is a disaccharide made of one glucose and one fructose molecule, making it a viable dual-carb option. However, many sports nutrition products optimize their ratios for maximum performance and digestibility.
What are hydrogels, and how do they work?
Hydrogels are sports drinks that form a gel-like consistency in the stomach, which allows for faster gastric emptying and potentially higher carbohydrate intake (up to 120 g/h) with less GI distress. They are typically used by athletes at higher intensity levels or with sensitive stomachs.
Can I use fruit juice for fuel during an endurance event?
Fruit juice contains natural sugars (fructose and glucose) but also has high concentrations of fructose and sometimes fiber, which can cause GI issues if consumed in large quantities during high-intensity exercise. It is not ideal for high-volume fueling during an event but can be used in small amounts during recovery.
What is gut training, and why is it important for carbohydrate intake?
Gut training involves practicing consuming race-day nutrition during long training runs to acclimate your digestive system to higher carbohydrate loads. This reduces the risk of stomach issues on race day and improves your ability to absorb and utilize fuel effectively.
Conclusion
Understanding the science behind carbohydrate absorption is the key to optimal fueling for endurance athletes. While no single type of sugar is the "best," combining multiple carbohydrates like glucose and fructose, often from sources like maltodextrin and fruit sugars, allows the body to absorb more energy more efficiently. Athletes can leverage specific sugar types and ratios before, during, and after exercise to maximize glycogen stores, sustain performance, and accelerate recovery. Always remember to practice your fueling strategy during training to ensure gut tolerance on race day.
Optional Outbound Link: Learn more about how the body uses sugars from MySportScience
Keypoints
- Combine Glucose and Fructose: For optimal absorption, use a carbohydrate blend that includes both glucose and fructose to utilize separate intestinal transporters and increase total fuel intake.
- Use the Right Ratio: Scientific evidence supports using a 1:0.8 glucose-to-fructose ratio for maximum carbohydrate oxidation, especially for higher intake levels.
- Prioritize Maltodextrin In-Race: Maltodextrin is an excellent glucose source for mid-race fueling due to its rapid absorption, high glycemic index, and minimal sweetness, making it easier to consume in large quantities.
- Fuel Post-Workout with Simple Sugars: Immediately after exercise, consume simple carbohydrates like dextrose with protein to quickly replenish glycogen stores and initiate the recovery process.
- Train Your Gut: Practice your fueling strategy during training sessions to train your digestive system to handle high carbohydrate intake and prevent gastrointestinal issues on race day.
Citations
["1.5.1": {"url": "https://www.trainingpeaks.com/blog/glucose-and-fructose-in-endurance-sport/"}, "1.5.4": {"url": "https://nduranz.com/blogs/blogs/carbohydrate-ratio-fueling"}, "1.7.3": {"url": "https://nduranz.com/blogs/blogs/maltodextrin-the-key-fuel-for-peak-athletic-performance"}, "1.8.3": {"url": "https://eu.nutrimuscle.com/blogs/news/dextrose-bienfaits"}, "1.11.3": {"url": "https://usecadence.com/blogs/science/ultramarathon-nutrition-guide"}]
