[Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: International Research Literature Translation and Commentary (No. 532)

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

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

Physiological Basis of Carbohydrate Loading

Glycogen stores in muscles and the liver are limited. Prolonged endurance exercise (typically exceeding 90 minutes) can easily lead to “hitting the wall” due to glycogen depletion. Carbohydrate loading strategies maximize glycogen stores in muscles and the liver by increasing carbohydrate intake proportion over several days before the race (while simultaneously maintaining or reducing training volume), thereby delaying the onset of hitting the wall.

Glucose to Fructose Ratio During Competition

Using only glucose-based carbohydrates, the absorption rate of glucose transporters (SGLT1) in the human intestine has a physiological upper limit (approximately 60 grams per hour). Exceeding this amount can easily cause gastrointestinal discomfort. Research has found that combining with fructose (absorbed via different transporters GLUT5) can increase the overall carbohydrate absorption capacity. This is also the physiological basis for the increasing popularity of “dual-carbohydrate/multi-carbohydrate source” sports supplements (glucose + fructose combination)—common ratios fall around 2:1 (glucose:fructose), which can raise the hourly carbohydrate intake limit to around 90 grams.

Comparison of Gastrointestinal Discomfort Incidence for Different Supplementation Strategies (Illustrative)

Core Research Conclusions and Practical Recommendations

• Pre-Race Loading Timeline: It is recommended to gradually increase the carbohydrate intake proportion (over 70% of total calories) 2-3 days before the race, while significantly reducing training volume, allowing sufficient time for glycogen storage.
• Gut Training: Gradually increase the carbohydrate intake amount and frequency during competition in long-term training to allow the intestine to adapt to high-volume carbohydrate absorption loads, which can significantly reduce the risk of gastrointestinal discomfort during actual competition.
• Regular Supplementation Timing: Instead of waiting until thirsty or hungry to supplement, it is recommended to set fixed time intervals (e.g., every 20-30 minutes) for small, frequent intakes to maintain stable blood sugar levels.
• Individualized Testing: Osmolarity and taste tolerance for different supplements vary from person to person. Major supplements must be tested in actual training or simulated races before major events to avoid trying new products for the first time on competition day.

Common Research Questions and Answers (FAQ)

Q: Will carbohydrate loading make you gain weight or become heavier?

A: The weight gain caused by short-term loading is mainly due to water (glycogen storage simultaneously locks in water). After the competition, as glycogen is consumed, the weight naturally subsides; it is not fat accumulation, so there is no need to worry excessively.

Q: Must carbohydrate supplementation during competition use a product mixed with glucose and fructose?

A: Not necessary, but if the race duration is longer (e.g., over 4 hours for a full marathon) and higher carbohydrate intake is needed, a mixed source indeed helps increase the absorption upper limit and reduce gastrointestinal burden.

References and Academic Citations

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

Related Topics Reading

• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: International Research Literature Translation and Commentary (No. 1372)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: International Research Literature Translation and Commentary (No. 406)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Latest Academic Literature Review and Training Practice (No. 1258)
• 【Research Review】Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Latest Academic Literature Review and Training Practice (No. 1375)