![Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Physical Characteristics of Elite Athletes (Article 928)](/media/articles/images/article-10526-928.png)

[Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Physical Characteristics of Elite Athletes (Article 928)

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

In the research field of the 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 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 the proportion of carbohydrate intake (typically reaching 8-12 grams per kilogram of body weight) in the 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 and found 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%, an effect 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 stable blood glucose levels. However, single-source 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 a “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 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, a “glucose:fructose = 2:1” dual-sugar fueling strategy is recommended to improve absorption efficiency and reduce the risk of gastrointestinal discomfort.
• Fueling timing plan: Begin fueling in small, frequent amounts 30-45 minutes after the race starts, and avoid 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 fluid and sodium intake to prevent high-concentration sugar solutions from worsening gastrointestinal osmotic imbalance and discomfort.

Common Research 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 the carbohydrate proportion 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 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 limit of a single sugar, allowing hourly carbohydrate intake to exceed 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”

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