[Research Review] Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Exploring the Relationship Between Clinical Medicine and Sports Performance (Article 922)

Reference Journal Source: International Journal of Sport Nutrition and Exercise Metabolism • International 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 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 distress. Research has found that combining fructose (absorbed via a different transporter, GLUT5) can increase the total amount of carbohydrate absorbed—this is 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 Distress Incidence Across Different Fueling Strategies (Illustrative)

Core Research Conclusions and Practical Recommendations

• Pre-race loading timeline: Gradually increase carbohydrate intake ratio (to over 70% of total calories) in the 2–3 days before competition, while significantly reducing training volume, to allow sufficient time for glycogen storage
• Gut training: Gradually increasing in-race carbohydrate intake volume and frequency during long-term training allows the gut to adapt to high carbohydrate absorption loads, significantly reducing the risk of gastrointestinal distress during actual competition
• Regularize fueling timing: Rather than waiting until thirsty/hungry to fuel, set fixed time intervals (e.g., every 20–30 minutes) for small, frequent intakes to maintain blood glucose stability
• Personalized testing: Osmolality and taste tolerance vary between individuals and products; be sure to test fueling strategies 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 you gain fat or weight?

A: The short-term weight gain from loading is primarily water (glycogen storage simultaneously retains water), which naturally subsides 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 mixed products for in-race fueling?

A: Not necessary, but for longer events (e.g., a full marathon over 4 hours) requiring higher carbohydrate intake, mixed 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 multiple-carbohydrate-source fueling.
2. Sports Medicine — Literature related to 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: Physical Characteristics of Elite Athletes (Article 247)
• Research Review: Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Latest Academic Literature Review and Training Practice (Article 910)
• Research Review: Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Physical Characteristics of Elite Athletes (Article 643)
• Research Review: Latest Report on Carbohydrate Loading Ratios and Gastrointestinal Tolerance in Long-Distance Endurance Running: Physical Characteristics of Elite Athletes (Article 1135)