Gut Training

Practicing race-day nutrition during training runs so the stomach can tolerate fuel under exertion.

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Understanding Gut Training

Gut training is the practice of deliberately consuming food and fluids during training runs to condition your digestive system for race-day fueling. Your GI tract, like your muscles, adapts to the demands placed on it — runners who regularly practice fueling during training experience significantly less stomach distress on race day.

During exercise, blood is diverted away from the gut toward working muscles, reducing digestive capacity by up to 60–80%. This is why eating during running causes nausea, cramping, and worse. But research shows the gut can be trained to tolerate more fuel during exercise: stomach emptying rate improves, intestinal absorption increases, and discomfort decreases.

Start small and build. Practice with your race-day fuel (gels, chews, or drink mix) during long runs, beginning with small amounts early in the run and gradually increasing over weeks. It takes 6–10 weeks of consistent practice to meaningfully train your gut. By race day, consuming 30–60g of carbs per hour should feel routine.

Key Facts: Gut Training

Key facts and insights about gut training that every endurance athlete should know.

Blood flow to the gut drops 60–80% durin

Blood flow to the gut drops 60–80% during intense exercise

Gut training takes 6–10 weeks of consist

Gut training takes 6–10 weeks of consistent practice to show results

Trained guts can absorb 30–60g of carbs/

Trained guts can absorb 30–60g of carbs/hour; untrained guts may handle only 20g before distress

30–50% of endurance athletes experience

30–50% of endurance athletes experience GI issues during racing

Pro Tips: Gut Training

Start gut training 3–4 months before your goal race, not 3 weeks before

Begin with half a gel on long runs, then progress to full gels as your gut adapts

Practice with the exact products you'll use on race day — different gels have different ingredients

If one gel brand causes issues, try another — ingredients like sugar alcohols and high fructose are common culprits

Frequently Asked Questions About Gut Training

The impact forces of running mechanically jostle the GI tract, and the upright posture compresses the abdomen. Cycling is lower-impact and the seated position reduces gut compression. This is why triathletes often do most of their fueling on the bike.

Try different fuel sources (real food vs. gels, different brands), reduce fructose intake, ensure adequate hydration, and avoid high fiber/fat in the 3–4 hours before running. Some runners have genuine sensitivities that gut training can't fully resolve — work with a sports dietitian if problems persist.