[Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Exploring the Relationship Between Clinical Medicine and Athletic Performance (Article 1366)

Reference Journal Source: International Journal of Sport Nutrition and Exercise Metabolism • International Scientific Research Findings Review 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, and 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 carbohydrate intake ratios (while maintaining or reducing training volume) in the days before competition, thereby delaying the onset of hitting the wall.

Glucose-to-Fructose Ratios in In-Race Fueling

When using glucose-based carbohydrates alone, the absorption rate of the intestinal glucose transporter (SGLT1) has a physiological ceiling (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 also the physiological basis for the growing popularity of “dual-source/multi-source” sports nutrition products (glucose + fructose combinations)—the common ratio falls around 2:1 (glucose:fructose), which can raise the hourly carbohydrate intake ceiling to approximately 90 grams.

Comparison of Gastrointestinal Discomfort Incidence Across Different Fueling Strategies (Illustrative)

Key Scientific Conclusions and Practical Recommendations

• Pre-race loading timeline: It is recommended to gradually increase carbohydrate intake (above 70% of total calories) 2-3 days before the race while significantly reducing training volume, allowing ample time for glycogen storage
• Gut training: Gradually increase in-race carbohydrate intake and frequency during long-term training so the gut adapts to high-volume carbohydrate absorption loads, which can significantly reduce the risk of gastrointestinal discomfort on race day
• Regularize fueling timing: Rather than waiting until thirsty/hungry, it is recommended to fuel in small, frequent amounts at fixed intervals (e.g., every 20-30 minutes) to maintain stable blood glucose levels
• Individualized testing: Osmolality and taste tolerance vary from person to person across different products; be sure to test your fueling strategy during training or simulation races before major events, and avoid trying new products for the first time on race day

Common Research Q&A (FAQ)

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

A: The weight gain from short-term loading is primarily water (glycogen storage simultaneously retains water), which will naturally subside as glycogen is depleted after the race. It is not fat accumulation, so there is no need for excessive concern.

Q: Is it necessary to use glucose-fructose blended products for in-race fueling?

A: Not necessary, but for longer events (e.g., marathons over 4 hours) requiring higher carbohydrate intake, blended sources can indeed help raise the absorption ceiling and reduce gastrointestinal burden.

References and Academic Citations

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

Further Reading

• 【科研導讀】長距離耐力跑中的碳水化合物加載比例與消化道耐受性的最新報告：臨床醫學與運動表現關係探討 (第 880 篇)
• 【科研導讀】長距離耐力跑中的碳水化合物加載比例與消化道耐受性的最新報告：臨床醫學與運動表現關係探討 (第 997 篇)
• 【科研導讀】長距離耐力跑中的碳水化合物加載比例與消化道耐受性的最新報告：臨床醫學與運動表現關係探討 (第 1144 篇)
• 【科研導讀】長距離耐力跑中的碳水化合物加載比例與消化道耐受性的最新報告：臨床醫學與運動表現關係探討 (第 1159 篇)