New 2025 Gut Training Science Elevates Endurance Athlete Performance

New research from the 2025 Joint Position Statement on exercise-induced gastrointestinal syndrome (EIGS) by Sports Dietitians Australia and the Ultra Sports Science Foundation highlights "gut training" as a key strategy for endurance athletes. This scientific consensus, published by Costa et al. in Sports Medicine, grades gut training as Grade I evidence, signaling its strong efficacy in improving athletic performance and reducing gastrointestinal distress Source.

Gut training involves the deliberate and progressive practice of consuming target carbohydrate rates during training sessions. This protocol aims to adapt an athlete's gastrointestinal tract, allowing for better absorption and tolerance of fuel during long, intense efforts.

What is Gut Training?

Gut training is a structured, multi-week protocol that involves increasing carbohydrate intake during exercise. It's not a quick fix for race week but rather a foundational element of competitive endurance preparation, much like interval training or strength work. The goal is to drive specific physiological adaptations in the digestive system.

The minimum effective dose for measurable adaptation is two weeks, but 8 to 12 weeks of consistent practice is recommended for optimal race day performance Source. For races lasting over three hours, a minimum of ten weeks of gut training is suggested.

How the Gut Adapts to Fueling

The gut adapts by upregulating specific intestinal transporters: SGLT1 and GLUT5. SGLT1 absorbs glucose and maltodextrin, saturating at approximately 60g of glucose per hour. Exceeding this can lead to gastrointestinal issues like bloating and cramping. GLUT5 absorbs fructose through a separate pathway.

Combining glucose and fructose allows athletes to absorb more than 90g/hr of carbohydrates, with some achieving up to 120g/hr. Repeated exposure to high-carbohydrate fueling increases the density and activity of SGLT1, making the gut more efficient at processing fuel. This means that if a product only lists maltodextrin or dextrose without fructose, an athlete will hit their absorption ceiling quickly, regardless of how much they consume.

Key Findings from the 2025 Position Paper

The Costa et al. 2025 paper ranked various interventions by evidence tier. Three strategies received Grade I evidence for being performance-enhancing and gut-protective:

1. Carbohydrate consumption during exercise (60–90 g/hr): This increases blood flow to the gut, mitigating the splanchnic ischemia that often causes EIGS. Studies show a significant reduction in gut barrier injury markers with this approach.
2. Two-week gut training protocols: This significantly reduces carbohydrate malabsorption, from clinical levels to near zero. A systematic review in 2023 found a 47% reduction in gut discomfort and 54% less carbohydrate malabsorption after just two weeks of targeted fueling at 30–90 g/hr.
3. Low-FODMAP eating 24–48 hours pre-race: This intervention can reduce gastrointestinal symptom severity by roughly 50%.

Conversely, three popular interventions were graded as ineffective:

• Probiotics: No measurable effect on gut barrier integrity, inflammation, or symptoms in endurance athletes.
• Glutamine: Findings were inconsistent and not clinically relevant for trained athletes.
• Chronic Low-Carbohydrate/Ketogenic Diets (LCHF): Studies showed these diets could actually increase gut barrier injury, with no a demonstrable symptom benefit.

Implementing a Gut Training Plan

Gut training should be applied to training sessions over 75 minutes, with a focus on progressive overload. A typical 10-week build for professional athletes progresses from 30–45 g/hr in the initial ''Foundation'' phase to 75–120 g/hr during the ''Refinement'' phase leading up to a race.

Common Mistakes to Avoid:

• Starting too close to race day: Two weeks is the minimum, not the optimal duration.
• Using glucose-only products: These cap carbohydrate absorption at 60 g/hr.
• Not training in race conditions: Heat, high intensity, and stress can all affect GI tolerance.
• Introducing new products on race day: Stick to what the gut is accustomed to.
• Confusing tolerance for the ceiling: Being comfortable at a certain intake level signals an opportunity to build further, not to stop.

Consistent gut training for 8–10 weeks can lead to reduced bloating and nausea, increased carbohydrate intake capacity, more stable energy, and fewer 'bonk' moments. It's a protocol designed to optimize fuel delivery and proven performance under race-like conditions.