Carbohydrate utilization during exercise is a key factor in optimizing performance and delaying the onset of fatigue in endurance activities. Ingesting exogenous carbohydrates (from food) helps preserve muscle glycogen, the primary fuel for prolonged exertion.
However, the digestive system's ability to absorb and oxidize these carbohydrates is limited by intestinal transporters. For a long time, recommendations focused on glucose alone. Today, it is accepted that combining glucose and fructose increases the absorption and utilization of ingested carbohydrates. But what is the right ratio to get the most benefit?
In this article, we will analyze the ideal glucose:fructose ratio according to the duration of the effort, based on the latest scientific research.
Why combine glucose and fructose?
The intestine has several specialized transporters for the absorption of carbohydrates:
• Glucose and glucose polymers (maltodextrins) are transported by SGLT1, which reaches a saturation threshold at approximately 60 g/h.
• Fructose uses another transporter, GLUT5, which does not compete with glucose and allows for the absorption of more carbohydrates.
When glucose and fructose are ingested together, the body can exceed the absorption limit of glucose alone and achieve exogenous oxidation of up to 1.7 g/min (102 g/h) instead of 1 g/min (60 g/h) with glucose alone.
The Ratio 2:1 vs. 1:0.8: What's the Difference?
Ratio 2:1 (Glucose:Fructose)
Historically, a 2:1 ratio has been proposed as optimal for increasing carbohydrate oxidation without causing digestive discomfort. This ratio allows for up to 50% greater absorption compared to glucose alone and improves energy availability.
📌 Key studies:
• Jeukendrup et al. (2004) showed that a glucose:fructose mixture in a 2:1 ratio allowed an oxidation of 1.5 g/min (90 g/h), compared to 1 g/min for glucose alone
• Currell & Jeukendrup (2008) demonstrated that a drink containing a 2:1 mixture improves performance by 8% on a 100 km time trial compared to glucose alone.
✅ Advantages of the 2:1 ratio:
• Suitable for most endurance efforts (cycling, marathon, triathlon).
• Increases absorption without overloading the digestive system.
• Easily assimilated for moderate to high intensities.
Ratio 1:0.8 (Glucose:Fructose)
More recent studies suggest that a ratio of 1:0.8 (or 1:0.85) would be even more effective on very long efforts (ultra-trails, Ironman, cycling tours > 5h).
📌 Key studies:
• Rowlands (2015) showed that the 1:0.8 ratio allows an oxidation of 1.7 g/min (102 g/h), representing a 45% increase compared to glucose alone
• O'Brien (2013) demonstrated better gastrointestinal tolerance with a ratio of 1:0.8 over prolonged efforts.
✅ Advantages of the 1:0.8 ratio:
• Optimizes exogenous carbohydrate oxidation beyond 4 hours of exertion.
• Improves intestinal tolerance by reducing osmotic load.
• Suitable for athletes looking to exceed 100-120g of carbohydrates per hour.
⚠️ Why not go below 0.8 in fructose?
Fructose is absorbed more slowly by the intestines and requires hepatic conversion to glucose before being used by the muscles. Excess fructose can cause digestive discomfort (bloating, diarrhea). A ratio of 1:0.8 appears to be the balance between optimal absorption and tolerance.
What Ratio Should Be Adopted Based on the Duration of the Effort?
👉 The 2:1 ratio remains a safe bet for most endurance efforts.
👉 The 1:0.8 ratio becomes more relevant for prolonged efforts, allowing higher oxidation and better digestive tolerance.
Practical Application: How to Use These Ratios?
• Products to favour: Gels, drinks and bars containing a mixture of glucose (or maltodextrin) and fructose in the right ratio.
• It can't be stressed enough: "Test during training!" Every athlete has a different intestinal tolerance. Testing the gradual increase in intake (from 60 to 120 g/h) helps avoid discomfort.
• Adapt to climatic conditions: In high heat, slightly increasing fructose can be beneficial as it generates less oxidation and metabolic stress than glucose.
Conclusion
The glucose:fructose combination is an effective strategy to improve carbohydrate oxidation and energy availability during exercise.
📌 In summary:
• For short efforts (<90 min), glucose alone is sufficient (60 g/h).
• For medium efforts (2-4h), a ratio of 2:1 is optimal (90 g/h).
• For long efforts (>4h), a ratio of 1:0.8 allows reaching up to 120 g/h.
The challenge is to individualize these intakes according to the intensity of the effort, digestive tolerance and performance objectives.
In endurance sports, nutrition isn't just about energy consumption, but also about the ability to absorb and use it efficiently. Adopting the right glucose-to-fructose ratio is a true optimization strategy that can transform your performance and comfort during exercise.
References
1 . Jeukendrup AE et al., “Exogenous carbohydrate oxidation rates increase with combined glucose-fructose ingestion”, Med Sci Sports Exerc, 2004.
2. Currell K, Jeukendrup AE., “Superior endurance performance with ingestion of multiple transportable carbohydrates”, Med Sci Sports Exerc, 2008.
3. Rowlands DS et al., “Glucose–fructose enhances performance”, J Appl Physiol, 2015.
4. O'Brien WJ et al., “Gastrointestinal comfort and substrate oxidation with different carbohydrate blends”, Int J Sport Nutr Exerc Metab, 2013.
💡 Try this: Adjust your carbohydrate intake according to your effort and observe the impact on your performance!
