【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Biomechanical Quantification Experiment Report (No. 688)

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

In the research field of the Road Running section, the latest biomechanical analyses and physiological studies have revealed more subtle performance insights. This research report is compiled from the cutting-edge literature of Sports Medicine Journal, providing a detailed analysis of the performance of subjects in both the experimental and control groups. This study explores the physiological adaptations, mechanical benefits, and their applications in training practice for athletes under long-term training or extreme events, 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 grams per kilogram of body weight) 1-3 days before a long-distance endurance event, combined with reduced training intensity, to promote a state of supercompensation in muscle and liver glycogen stores. This study compared the traditional one-week loading method 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

During long-distance endurance events such as marathons, athletes need to consume 60-90 grams of carbohydrates per hour to maintain blood glucose stability. However, single sugars (such as pure glucose) have a physiological limit to their intestinal absorption rate; 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 over 90 grams, 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 control group and multi-dimensional data comparison:

Core Research 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 grams per kilogram of body weight 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 during an official race.
• Hydration and electrolyte synchronization: Carbohydrate fueling should be paired with adequate water and sodium intake to avoid high-concentration sugar solutions causing an imbalance in gastrointestinal osmotic pressure and worsening discomfort.

Common Research Q&A (FAQ)

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

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

Q: Why is glucose plus fructose recommended for in-race fueling rather than 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 over 90 grams 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: Advances in Frontier Exercise Physiology Research (No. 628)
• 【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: Study of Elite Athletes’ Physical Characteristics (No. 928)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Advances in Frontier Exercise Physiology Research (No. 340)