The Most Efficient Source of Glucose for Runners

November 25, 2025 •

2 min read

According to sports science, the human body's carbohydrate transporters are limited in how much glucose they can absorb per hour, with the cap typically around 60 grams. To exceed this limit and maximize carbohydrate absorption, what is the most efficient source of glucose for runners to use during prolonged exercise? The answer lies not in a single ingredient, but in a specific combination of different sugars.

Quick Summary

Efficient fueling for runners involves a strategic blend of glucose and fructose. Using dual-transportable carbohydrates allows for higher absorption rates, delays fatigue, and minimizes gastrointestinal distress during extended efforts.

Key Points

Dual-Carb Strategy: Combining glucose and fructose is the most efficient fueling method for runners, allowing for higher absorption rates (~90g/hr) by using different intestinal transporters.
Optimal Ratios Matter: For high carbohydrate intake during prolonged exercise, a 2:1 or even 1:0.8 glucose-to-fructose ratio is often recommended.
Timing is Key: Use complex, low-GI carbs for pre-event loading and daily nutrition, and fast-acting, dual-carb sources for during-race fueling and immediate recovery.
Train Your Gut: Tolerance for high carbohydrate intake during exercise can be developed. Practice your race-day fueling strategy during training runs.
Fuel According to Intensity and Duration: Long-distance, high-intensity efforts lasting over 90 minutes require consistent carbohydrate intake.
Don't Forget Recovery: Post-run nutrition is crucial for glycogen replenishment and repair.

The Science of Dual Carbohydrate Absorption

Research indicates that endurance athletes can absorb more carbohydrates per hour by combining glucose and fructose compared to using glucose alone. This is because glucose and fructose use different intestinal transporters. Utilizing both pathways can increase total carbohydrate absorption to 90 grams per hour or more. This strategy can enhance energy delivery and benefit athletes during extended exercise. Common dual-carb mixes often include maltodextrin (a glucose source) and fructose.

The Importance of Optimal Ratios

The ratio of glucose to fructose impacts the effectiveness of dual-carb blends. Ratios around 2:1 are effective for consuming about 90 grams per hour, balancing absorption and reducing GI issues. For higher intake, a 1:0.8 ratio may be more effective. Gradually increasing carbohydrate intake during training can also improve tolerance.

Practical Fueling Strategies for Runners

The timing and type of carbohydrate are crucial. Complex carbs are suitable for daily diet and pre-event meals (hours before), while fast-acting simple sugars are best during and immediately after a run for quick energy.

Pre-Run Fueling

Complex Carbohydrates: Focus on foods like rice and pasta for carb loading before a long race.
Simple Carbs (Closer to Run): A banana or sports drink 30-60 minutes before can provide a quick boost.

During-Run Fueling

For runs over 90 minutes, aim for 30-60 grams of carbs hourly, or 90+ grams with a dual-carb mix for intense events.

Energy Gels: Many gels offer a fast-acting glucose-fructose mix.
Sports Drinks: These provide carbs and electrolytes, with dual-carb options aiding both fueling and hydration.
Carbohydrate Chews and Bars: Alternatives for fueling on the go.

Post-Run Recovery

Consuming high-GI carbs within 30-60 minutes post-run is key for glycogen replenishment.

Comparison Table: Fueling Options


Fuel Source	Carbohydrate Type	Absorption Speed	Primary Use Case	Best For	Considerations
Energy Gels (Dual-Carb)	Maltodextrin & Fructose	Very Fast	During intense exercise	Long runs, marathons	Requires water, gut training needed for high intake
Sports Drinks (Dual-Carb)	Maltodextrin & Fructose	Fast	Hydration & Fueling	Long runs, hot weather	Can be bulky to carry, follow mix ratios
Bananas	Simple Sugars (Glucose & Fructose)	Fast	Quick energy boost	Pre-run snack, mid-run fuel	Can cause GI distress in large quantities due to fiber
Potatoes/Rice (White)	High-GI Complex	Moderate	Carb-loading, recovery	Pre-race meal (night before)	Lower fiber helps avoid GI issues, not for during run
Oatmeal (Whole Grain)	Low-GI Complex	Slow	Sustained energy	Daily nutrition, pre-run (hours before)	High fiber can cause GI issues closer to a run

Training the Gut for Efficiency

Improving your gut's ability to handle carbs during runs is important. Gradually increase your hourly carbohydrate intake during training. Experiment with different fueling products to find what works best.

Conclusion

The most efficient source of glucose for runners is a combination with fructose, leveraging separate transporters to maximize absorption beyond glucose-only limits (up to 90+ grams/hour). A strategic approach includes complex carbs for daily fuel and pre-event loading, fast-acting dual-carb sources during intense efforts, and high-GI carbs for post-run recovery. Practice your fueling strategy in training to ensure gut tolerance on race day.

Frequently Asked Questions

The body is limited in how much glucose it can absorb per hour due to a finite number of SGLT1 transporters, capping glucose-only absorption at around 60 grams per hour. Attempting to consume more can cause digestive issues.

Fructose is critical for endurance athletes because it uses a different transporter (GLUT5) than glucose, allowing the body to absorb more total carbohydrates per hour when consumed together.

The night before a race, runners should focus on a carbohydrate-rich meal with low fiber to fill glycogen stores without causing GI distress. Examples include white pasta, rice, or potatoes. Avoid high-fat, heavy foods.

During a race, runners should use simple carbohydrates with a high glycemic index (like those in gels, chews, and sports drinks) for quick energy delivery. Complex carbohydrates are too slow.

Gut training is the practice of consistently consuming carbohydrates during training runs to improve the digestive system's tolerance and absorption capacity. This helps prevent GI issues during race day.

For runs lasting over 90 minutes, runners should aim for 30-60 grams of carbohydrates per hour. For more intense, longer events, a dual-carb mix can push this intake to 90 grams or more per hour.

Honey contains both glucose and fructose, making it a viable option. For precise fueling during intense races, commercially prepared products with specific ratios are often preferred.