[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 1339)

Reference 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.

The 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 for 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 amount of carbohydrate absorbed—this is also the physiological basis for the growing popularity of “dual/multiple carbohydrate 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 Rates Across Different Fueling Strategies (Illustrative)

Key Scientific Conclusions and Practical Recommendations

• Pre-race loading timeline: It is recommended to gradually increase carbohydrate intake (to over 70% of total calories) 2–3 days before the race while significantly reducing training volume, allowing ample time for glycogen storage
• Gut training: Gradually increasing in-race carbohydrate intake volume and frequency during long-term training helps the gut adapt to high carbohydrate absorption loads, significantly reducing the risk of gastrointestinal discomfort during the actual race
• Regularize fueling timing: Rather than waiting until thirsty or hungry, it is recommended to fuel at fixed intervals (e.g., every 20–30 minutes) in small, frequent amounts to maintain stable blood glucose
• Personalized 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 mainly water (glycogen storage simultaneously retains water), which will naturally subside after the race as glycogen is depleted. 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., a full marathon lasting 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 on absorption rates of multiple-carbohydrate-source supplements.
2. Sports Medicine — Literature on gut training and gastrointestinal tolerance in endurance sports.

Related Reading

• 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 1273)
• 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 1246)
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