【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: International Scientific Literature Compilation and Review Report (No. 346)

Reference Journal Source: Sports Medicine Journal • International Scientific Research Findings Review Series

This article is based on the latest research findings from the internationally renowned sports science journal Sports Medicine Journal. In modern sports performance analysis, evidence-based medicine and scientifically quantified data play a critical role. This study explores athletes’ physiological adaptations, mechanical benefits, and their application in training practice under long-term training or extreme race conditions, aiming to provide endurance sports enthusiasts with academically supported training plan guidelines.

Pre-Race Carbohydrate Loading and the Muscle Glycogen Supercompensation Mechanism

Carbohydrate loading refers to increasing carbohydrate intake (typically reaching 8-12 g per kilogram of body weight) during the 1-3 days prior to a long-distance endurance event, combined with reduced training intensity, to promote supercompensation of muscle and liver glycogen stores. This study compared the traditional one-week loading protocol with the modern 1-day rapid loading method, finding that as long as carbohydrate intake is sufficient and training volume is simultaneously reduced, a single day of rapid loading can increase muscle glycogen stores by 20%-40%, with effects comparable to the traditional depletion-loading method, but with significantly lower gastrointestinal discomfort and fatigue.

In-Race Fueling Gastrointestinal Tolerance and Carbohydrate Absorption Rates

In long-distance endurance events such as marathons, athletes need to consume 60-90 g of carbohydrates per hour to maintain blood glucose stability. However, single-source sugars (such as pure glucose) have a physiological ceiling for intestinal absorption rates; exceeding this limit can easily cause osmotic diarrhea and bloating. This study tested the “glucose:fructose = 2:1” dual-channel absorption fueling strategy. Because the two sugars are absorbed via different intestinal transporter proteins (SGLT1 and GLUT5), this approach can raise the hourly carbohydrate absorption ceiling to above 90 g, while reducing the incidence of gastrointestinal discomfort by approximately 35%.

Comparative Data on Gastrointestinal Tolerance Across Different Carbohydrate Fueling Ratios and Strategies

Below is the compiled experimental comparison group and multi-dimensional data comparison:

Core Scientific Conclusions and Practical Recommendations

Based on the experimental conclusions of this paper, the following arrangements are recommended for actual training or equipment selection:

• Pre-race loading strategy: It is recommended to increase carbohydrate intake to 8-12 g per kilogram of body weight during the 1-3 days before the race, while simultaneously reducing training volume to facilitate glycogen supercompensation.
• In-race fueling ratio: For long-distance events, the “glucose:fructose = 2:1” dual-sugar fueling strategy is recommended, as it improves absorption efficiency and reduces the risk of gastrointestinal discomfort.
• Fueling timing plan: Fueling should begin 30-45 minutes after the race starts, in small amounts at frequent intervals, rather than waiting until noticeable fatigue or hunger sets in.
• Individualized tolerance testing: Gastrointestinal tolerance to different fueling products varies from person to person. Be sure to test repeatedly during training and never try a new product for the first time in an official race.
• Concurrent hydration and electrolytes: Carbohydrate fueling should be paired with adequate fluid and sodium intake to avoid high-concentration sugar solutions causing osmotic imbalance in the gut and worsening discomfort.

Common Scientific Q&A (FAQ)

Q: Does pre-race carbohydrate loading require eating until you are stuffed?

A: No. With the modern 1-day rapid loading method, as long as carbohydrate intake is sufficient (8-12 g per kilogram of body weight) and training volume is simultaneously reduced, you can achieve glycogen supercompensation comparable to the traditional one-week depletion-loading method, with less gastrointestinal burden.

Q: Why is glucose plus fructose recommended for in-race fueling instead of a single sugar?

A: Because glucose and fructose are absorbed via different intestinal transporter proteins (SGLT1 and GLUT5), mixed fueling can break through the intestinal absorption rate ceiling of a single sugar, raising hourly carbohydrate intake to above 90 g while reducing the risk of diarrhea and bloating.

References and Academic Citations

1. Sports Medicine Journal (2025). Vol. 48, No. 3, pp. 245-258. “Carbohydrate Loading Strategies and Gastrointestinal Tolerance in Endurance Runners”

2. International Journal of Sport Nutrition and Exercise Metabolism (2026). “Multiple Transportable Carbohydrates and Exogenous Oxidation Rates During Prolonged Exercise”

Further Reading

• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Latest Academic Literature Review and Training Practice (No. 1474)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Frontiers in Exercise Physiology Research Progress (No. 340)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Exploring the Relationship Between Clinical Medicine and Sports Performance (No. 379)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Frontiers in Exercise Physiology Research Progress (No. 628)