The Role of Glucose and Fructose


Understanding Carbohydrate Absorption for Enhanced Performance


Endurance sports, whether you're a seasoned athlete or a beginner, demand a lot from your body. One key to maintaining high-level performance is understanding how your body utilizes energy sources, particularly carbohydrates. In this article, we'll explore how combining glucose and fructose can optimize energy utilization during prolonged physical activities.


Carbohydrate Transporters: SGLT1 and GLUT5


Our bodies have specific transporters for absorbing different types of sugars. Glucose is absorbed through the SGLT1 transporter, while fructose utilizes the GLUT5 transporter. When you consume only glucose, the SGLT1 transporters can become saturated, limiting glucose absorption to about 60 grams per hour.

Endurance track 1

Why Mix Glucose and Fructose?
By incorporating fructose, which uses a separate transporter, you can increase your total carbohydrate absorption, thus enhancing available energy. This mixed intake leads to greater total carbohydrate oxidation than consuming glucose alone. This is because while glucose transporters may be saturated, fructose can still be absorbed, allowing for additional carbohydrate uptake.


The Benefits of Co-Ingesting Glucose and Fructose
1. During prolonged exercise, maintaining a high carbohydrate oxidation rate is crucial for sustaining high-intensity performance. The combined absorption of glucose and fructose ensures a steady energy supply.
2. Consuming high amounts of glucose alone can lead to gastrointestinal issues. By using both glucose and fructose, this risk is minimized, as fructose absorption doesn’t compete with glucose, thereby reducing gastrointestinal stress.
3. The mix allows the body to maintain energy levels over longer periods, essential in endurance sports where conserving energy is crucial.


Optimizing Carbohydrate Mixtures for Maximum Absorption

While about 60 grams of glucose can be absorbed per hour, adding fructose can further enhance this absorption. Ratios of 0.8:1 (fructose to glucose) are considered optimal for rapid absorption. Such mixtures allow for higher carbohydrate intake, critical in high-intensity and long-duration activities.

Endurance Athletes running on track


Practical Tips for Endurance Athletes


1. Start with a 0.8:1 fructose-to-glucose ratio and adjust based on your personal tolerance and performance needs.
2. Gradually increase your carbohydrate intake during training to adapt your digestive system.
3. Always pair your carbohydrate intake with adequate hydration to facilitate absorption and reduce gastrointestinal discomfort.
4. Practice your fueling strategy during training sessions to mimic race conditions.

WorldTour cyclists, who engage in high-intensity cycling, often consume between 100-120 grams of carbohydrates per hour. This high intake is due to the intense demands of professional cycling, where maintaining high levels of glucose for muscular and cognitive function is crucial. The ability to absorb and utilize such high amounts of carbohydrates is often a result of specialized training and adaptation, allowing their bodies to efficiently process these carbohydrates during high-intensity efforts. For broader endurance activities, newer studies suggest an intake of 70-90 grams per hour. The specific intensity that correlates with this range can vary based on the sport and the athlete's conditioning. Generally, this recommendation applies to moderate to high-intensity endurance activities. These activities are typically characterized by sustained effort that is not maximal but still requires a significant and continuous energy output.


Carbohydrate Needs Based on Event Duration:
For events lasting 4-5 hours, a higher carbohydrate intake is often necessary to maintain optimal performance. This is because glycogen stores (the body's stored form of carbohydrates) are limited and can be depleted during such durations of exercise. Athletes might aim for the higher end of the 60-90 grams per hour range, depending on their tolerance and the event's intensity.
In ultra-endurance events, carbohydrate needs are complex and can vary significantly. While high carbohydrate intake is still crucial, the intensity is often lower compared to shorter events, which can affect the rate of carbohydrate utilization. Additionally, gastrointestinal comfort and the ability to consume and digest food become more significant factors over longer durations. Athletes might consume lower rates of carbohydrates per hour compared to shorter events but focus more on continuous and consistent intake to prevent energy dips and maintain endurance.

In Conclusion
Understanding how your body absorbs and utilizes carbohydrates can significantly impact your endurance performance. By strategically combining glucose and fructose, you can enhance your energy levels, maintain high-intensity performance for longer durations, and minimize the risk of gastrointestinal distress.

RAW Endurance Athletes sprinting

 

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References
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during exercise. Sports medicine (Auckland, N.Z.).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4008807/
LJ. et al. (2015.). [performance enhancement by carbohydrate intake during sport: Effects of
carbohydrates during and after high-intensity exercise]. Nederlands tijdschrift voor
geneeskunde. https://pubmed.ncbi.nlm.nih.gov/25970669/
Urdampilleta A. et al. (2020.Jul.). Effects of 120 vs. 60 and 90 g/h carbohydrate intake during a
trail marathon on neuromuscular function and high intensity run capacity recovery.
Nutrients. https://pubmed.ncbi.nlm.nih.gov/32679728/
Viribay, A. et al. (2020, May 11). Effects of 120 g/h of carbohydrates intake during a mountain
marathon on exercise-induced muscle damage in elite runners. MDPI.
https://www.mdpi.com/2072-6643/12/5/1367

March 05, 2024 — Dominic Kuza

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