Carbohydrate Oxidation Rate Ceiling: The Scientific Basis of the 90g-Per-Hour Dual-Carbon-Source Strategy

Introduction

“60 grams of carbohydrates per hour is the limit, right?” This claim was popular in sports science for a long time, until a series of studies by Jentjens and Jeukendrup overturned this assumption. Carbohydrate absorption of 90 grams, or even 120 grams, per hour is achievable—but only if you choose the right combination of carbohydrate types.

This discovery completely changed fueling strategies in professional road racing and provided a new scientific foundation for fueling plans in long-distance challenges such as Taiwan’s round-island rides and Formosa 900. This article will analyze, from the perspective of intestinal physiology, why the dual-carbon-source strategy can break through the oxidation rate bottleneck, and how to apply it in actual riding.

The Bottleneck of Intestinal Glucose Absorption

To understand the dual-carbon-source strategy, you must first understand how the small intestine absorbs carbohydrates:

Transporter Protein Saturation

Specific active transporter proteins on the surface of small intestinal epithelial cells are responsible for carbohydrate absorption:

Key Finding: SGLT1’s glucose transport capacity is approximately 60 grams per hour. Glucose exceeding this amount remains in the small intestine and may cause osmotic diarrhea—this is the physiological basis for the “60 grams per hour limit.”

The Principle of Breaking the Bottleneck with Dual Carbon Sources

Glucose and fructose use different transporter proteins, so they can be “absorbed in parallel” rather than “absorbed competitively”:

• Glucose (60 g/hr, SGLT1 saturated) + Fructose (30 g/hr, GLUT5 saturated) = 90 g/hr total absorption
• With further optimization of fructose intake (GLUT5 upregulation after training), some studies show it can reach 110–120 g/hr

Supporting Data from Scientific Research

Several key studies have established the scientific foundation for the dual-carbon-source strategy:

• Jeukendrup (2010) meta-analysis: The maximum oxidation rate for a single carbohydrate (glucose) is 1.0 g/min (60 g/hr), while a 2:1 glucose:fructose mixture can reach 1.4–1.75 g/min (84–105 g/hr)
• Currell & Jeukendrup (2008): The 2:1 maltodextrin:fructose group improved 2-hour time trial performance by 8% compared to the pure glucose group
• Costa et al. (2017): Gut training can further increase fructose absorption rates by upregulating GLUT5 expression

Optimal Carbon Source Ratios and Food Choices

Recommended Glucose:Fructose Ratios

• 2:1 ratio (glucose:fructose): The most extensively studied, suitable for most riders
• 1:0.8 ratio: Some studies show higher fructose ratios work better for certain individuals
• To avoid: Pure fructose (HFCS high-fructose corn syrup) carries a high risk of gastrointestinal discomfort when exceeding 40 g/hr

Carbon Source Analysis of Common Fueling Products

Fueling Plan Design for Long-Distance Riding in Taiwan

Scenario 1: Formosa 900 (900 km around Western Taiwan)

Hourly fueling targets (rides over 5 hours):

• Carbohydrates: 80–90 g/hr (dual carbon source)
• Fluids: 500–800 mL/hr (adjusted based on sweat rate)
• Sodium: 500–700 mg/hr

Recommended fueling plan (every 45–60 minutes):

• 1 dual-carbon-source energy gel (40g carbs)
• 150 mL diluted sports drink (15g carbs)
• Or: 1 rice ball (35g carbs) + 150 mL fruit juice (15g carbs)

Scenario 2: Wushan Climbing Challenge (3–5 hours)

• Riding intensity is high, gastrointestinal blood flow is reduced, making easily digestible liquid dual-carbon sources more necessary
• Recommendation: energy gels + water (rather than solid food), replenished every 30 minutes
• Temperatures are low at the summit, making liquid fueling more acceptable

The Importance of Gut Training

The dual-carbon-source strategy cannot be attempted for the first time just one week before a race. The gut needs training to accept high-carbohydrate fueling:

1. Regularly consume solid food while riding (not relying only on water) to cultivate the gut’s ability to digest during exercise
2. Fuel according to plan during 2–3 long training rides per week, rather than training fasted / with water only
3. Gradually increase fueling frequency and amounts to allow the gut to adapt to high-throughput transport
4. Complete gut adaptation typically requires 4–8 weeks

Practical Recommendations

• When purchasing fueling products, prioritize formulas combining glucose (or maltodextrin) + fructose, rather than pure glucose or pure maltodextrin
• Test high-carbohydrate fueling (> 60 g/hr) for the first time during training sessions, not directly in competition
• Excessively high fructose ratios (over 40% fructose) cause gastrointestinal discomfort in some individuals; personal testing is not optional
• The dual-carbon-source strategy is only necessary for rides exceeding 2.5 hours; for short, high-intensity efforts (< 90 minutes), water and simple sugars suffice

Conclusion

Saturation of the small intestine’s transporter proteins is not an insurmountable obstacle. The dual-carbon-source strategy opens a wider fuel supply channel for long-distance riders. By understanding the respective absorption mechanisms of glucose and fructose, choosing products with the correct ratio, and improving absorption efficiency through gut training, you can still have fuel in the final 200 km of Formosa 900—rather than relying on sheer willpower. Remember: fueling is the fourth discipline, and it deserves the same serious practice as your pedaling technique.

Related Reading

• A Practical Guide to Consuming 120g of Carbohydrates Per Hour While Riding
• Decoding Pro Riders’ 120g Per Hour Carbohydrate Strategy: The Latest Sports Nutrition Science
• Breaking the Carbohydrate Oxidation Ceiling During Exercise: New Research on the 120g/Hour Glucose Plus Fructose Mix
• 90 or 120 Grams of Carbs Per Hour on Race Day? Interpreting the Latest Intake Limits