[Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Biomechanical Quantitative Experimental Report (No. 739)

Reference Journal Source: International Journal of Sport Nutrition and Exercise Metabolism • International Scientific Research Review Series

This article explores the balance strategy between carbohydrate loading ratios and gastrointestinal tolerance for long-distance endurance runners.

Physiological Basis of Carbohydrate Loading

Muscle and liver glycogen stores are limited. Prolonged endurance exercise (typically exceeding 90 minutes) often leads to “hitting the wall” due to glycogen depletion. Carbohydrate loading strategies maximize muscle and liver glycogen stores by increasing the proportion of carbohydrate intake in the days leading up to a race (while maintaining or reducing training volume), thereby delaying the onset of hitting the wall.

Glucose to Fructose Ratio for Intra-Race Nutrition

When using glucose-based carbohydrates alone, the human intestinal glucose transporter (SGLT1) has a physiological absorption limit (approximately 60g per hour); exceeding this amount often leads to gastrointestinal discomfort. Research has found that combining fructose (absorbed via a different transporter, GLUT5) can increase the total amount of carbohydrate absorption. This is the physiological basis for the growing popularity of “dual-source/multi-source” sports supplements (glucose + fructose combinations)—a common ratio is around 2:1 (glucose:fructose), which can increase the hourly carbohydrate intake limit to approximately 90g.

Comparison of Gastrointestinal Discomfort Incidence by Nutrition Strategy (Illustrative)

Core Scientific Conclusions and Practical Recommendations

• Pre-race Loading Schedule: It is recommended to gradually increase the proportion of carbohydrate intake (to over 70% of total calories) 2-3 days before the race, while significantly reducing training volume to allow sufficient time for glycogen storage.
• Gut Training: Gradually increase the intake amount and frequency of intra-race nutrition during long-term training. Allowing the gut to adapt to high-flow carbohydrate absorption loads can significantly reduce the risk of gastrointestinal discomfort during official races.
• Regularized Nutrition Timing: Rather than waiting until you are thirsty or hungry, it is recommended to set fixed time intervals (e.g., every 20-30 minutes) for small, frequent intake to maintain stable blood glucose levels.
• Personalized Testing: The osmolality and taste tolerance of different supplements vary from person to person. Be sure to test your nutrition strategy during training or simulation races before major events to avoid trying new products for the first time on race day.

Common Scientific Q&A

Q: Will carbohydrate loading make me gain fat or weight?

A: The weight gain caused by short-term loading is primarily water (glycogen storage binds water). This will naturally subside after the race as glycogen is consumed; it is not fat accumulation, so there is no need for excessive concern.

Q: Is it necessary to use glucose-fructose mixed products for intra-race nutrition?

A: It is not strictly necessary, but if the race duration is long (e.g., a full marathon taking over 4 hours) and a higher carbohydrate intake is required, mixed sources do help increase the absorption limit and reduce gastrointestinal burden.

References and Academic Citations

1. International Journal of Sport Nutrition and Exercise Metabolism — Research on absorption rates of multi-source carbohydrate supplements.
2. Sports Medicine — Literature on gut training and gastrointestinal tolerance in endurance sports.

Related Topic Reading

• [Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Biomechanical Quantitative Experimental Report (No. 715)
• [Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Biomechanical Quantitative Experimental Report (No. 622)
• [Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Biomechanical Quantitative Experimental Report (No. 61)
• [Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Biomechanical Quantitative Experimental Report (No. 541)