[Research Guide] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: A Study on the Physical Characteristics of Elite Athletes (Article 1387)

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

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

Physiological Basis of Carbohydrate Loading

Muscle and liver glycogen stores are limited. Prolonged endurance exercise (typically exceeding 90 minutes) can easily lead 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 in Race-Day Fueling

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

Comparison of Gastrointestinal Discomfort Incidence Rates for Different Fueling Strategies (Illustrative)

Core Research Conclusions and Practical Recommendations

• Pre-Race Loading Timeline: It is recommended to gradually increase the proportion of carbohydrate intake (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 increasing the amount and frequency of carbohydrate intake during fueling in long-term training allows the gut to adapt to high-flow carbohydrate absorption loads, significantly reducing the risk of gastrointestinal discomfort during the actual race.
• Regularized Fueling Timing: Rather than waiting for thirst/hunger to refuel, it is recommended to set fixed time intervals (e.g., every 20-30 minutes) for small, frequent feedings to maintain stable blood sugar levels.
• Personalized Testing: The osmolality and taste tolerance of different supplements vary from person to person. Before a major race, it is essential to test the fueling strategy during training or simulated races, avoiding trying new products for the first time on race day.

Common Research Q&A (FAQ)

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

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

Q: Is it necessary to use glucose-fructose mixed products for race-day fueling?

A: It is not mandatory, but if the race duration is long (e.g., a marathon over 4 hours) and a high carbohydrate intake is required, mixed sources do help increase the absorption ceiling and reduce gastrointestinal burden.

References and Academic Citations

1. International Journal of Sport Nutrition and Exercise Metabolism — Research directions related to the absorption rate of multi-source carbohydrate fueling.
2. Sports Medicine — Literature related to gut training and gastrointestinal tolerance in endurance sports.

Related Topic Reading

• [Research Guide] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: A Study on the Physical Characteristics of Elite Athletes (Article 1390)
• [Research Guide] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: A Study on the Physical Characteristics of Elite Athletes (Article 904)
• [Research Guide] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: A Review of the Latest Academic Literature and Training Practices (Article 1375)
• [Research Guide] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: A Study on the Physical Characteristics of Elite Athletes (Article 586)