Eat More, Race Faster: A Guide to Training Your Gut for High Carb Intake

Most endurance athletes spend hundreds of hours training their muscles, heart, and lungs. Yet, they often neglect a critical component that can make or break race day: the gastrointestinal (GI) tract.

The gut is the gateway for delivering the carbohydrates and fluids your body needs during prolonged exercise (¹). Unfortunately, GI symptoms are incredibly common, especially in running and are a leading cause of race withdrawals (²).

The good news? Research shows the gastrointestinal system is highly adaptable. Just as you train your legs for a marathon, you can "train your gut" to absorb more fuel and eliminate discomfort (¹).

What is Gut Training?

Gut training is the systematic process of exposing your digestive system to progressively higher carbohydrate and fluid intakes during your workouts. The goal is to improve your body's tolerance and absorption capacity before you reach the start line.

1. Boosting Your Absorption Capacity

During any exercise lasting longer than two hours, your performance is limited by how fast your intestines can absorb fuel, not just how much you eat (³).

• The Science: Athletes who regularly consume carbs during training develop a better ability to absorb them (⁴).

• The Transporter Effect: Research indicates that eating a high-carb diet for two weeks can significantly increase the "pumps" (SGLT 1) in your intestinal lining that move sugar into your bloodstream. Increasing your daily carb intake from 40% to 70% can potentially double these transporters (¹).

2. Reducing Gastrointestinal Distress:

Training the gut helps stop runners feeling symptoms of bloating, nausea or diarrhea through several mechanisms: improving how fast the stomach empties, reducing feelings of fullness, and helping the body handle larger fluid volumes (¹).

A study on elite cyclists showed that 28 days of a high-carb diet led to better "carbohydrate oxidation" meaning the body burned the fuel instead of letting it sit in the gut (⁵). This efficiency reduces the risk of bloating and cramping caused by unabsorbed sugar sitting in the intestines.

3. Improving Performance Outcomes

When your body can utilize more of the fuel you consume, you maintain energy levels longer and delay fatigue (⁶). By systematically training the gut, you ensure a steady power output throughout your entire event.

Gut Training vs. Carbohydrate Periodization

It is important to distinguish between these two popular strategies, as they serve very different purposes (⁷):

• Gut Training: Its sole purpose is to maximize carbohydrate absorption and tolerance. You do this by consistently practicing your high-carb race fueling during training sessions (¹).

• Carbohydrate Periodization: Also known as "Train Low," this involves alternating between low-carb and high-carb sessions to improve metabolic flexibility and fat burning.

While periodization helps with metabolism, gut training is what ensures you can actually digest your race-day fuel when the intensity is high.

How to Implement Gut Training

Because the intestine is so adaptable, you should begin practicing your race-day nutrition strategy several weeks before your event (⁸).

• Start Gradually: Begin with moderate carbohydrate intakes and increase the amount every few weeks.

• Be Consistent: Don't just save your "race fuel" for the weekend. Incorporate carb feeding into regular training sessions to build tolerance (¹).

• Simulate Race Conditions: Practice with the exact gels, drinks, and bars you plan to use on race day to ensure your gut is familiar with the specific formulas (⁴).

• Allow Time for Adaptation: It typically takes at least 2 to 4 weeks of consistent training for the gut to adapt to higher loads.

Conclusion

Your gut is a performance organ. By treating nutrition as a skill that can be trained, you can maximize your fueling capacity and minimize the risk of GI complications that could compromise your hard-earned results.

References

1. Jeukendrup, A. E. (2017). Training the gut for athletes. Sports Medicine, 47(Suppl 1), 101-110. https://doi.org/10.1007/s40279-017-0690-6

2. Costa, R. J. S., et al. (2017). Systematic review: Exercise-induced gastrointestinal syndrome - implications for health and intestinal disease. Alimentary Pharmacology & Therapeutics, 46(3), 246-265. https://doi.org/10.1111/apt.14157

3. Jeukendrup, A. E., & Jentjens, R. (2000). Oxidation of carbohydrate feedings during prolonged exercise: Current thoughts, guidelines and directions for future research. Sports Medicine, 29(6), 407-424. https://doi.org/10.2165/00007256-200029060-00004

4. Jeukendrup, A. E. (2014). A step towards personalized sports nutrition: Carbohydrate intake during exercise. Sports Medicine, 44(Suppl 1), 25-33. https://doi.org/10.1007/s40279-014-0148-z

5. Martinez, I. G., et al. (2023). The effect of gut-training and feeding-challenge on markers of gastrointestinal status in response to endurance exercise: A systematic literature review. Sports Medicine, 53(6), 1175-1200. https://doi.org/10.1007/s40279-023-01841-0

6. Cox, G. R., et al. (2010). Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. Journal of Applied Physiology, 109(1), 126-134. https://doi.org/10.1152/japplphysiol.00950.2009

7. Jeukendrup, A. E. (2017). Periodized nutrition for athletes. Sports Medicine, 47(Suppl 1), 51-63. https://doi.org/10.1007/s40279-017-0694-2

8. Burke, L. M., et al. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(Suppl 1), S17-S27. https://doi.org/10.1080/02640414.2011.585473