Can you really train your gut?

Gut training is one of endurance nutrition’s most discussed and least implemented ideas. Most athletes accept it in theory, then proceed to fuel on race day in ways they’ve never systematically practiced. This is a reliable way to produce stomach distress on race day.

What Gut Training Actually Means

The term encompasses two distinct, evidence-based adaptations.

The first is an increase in absorption sites. A 2010 study by Cox and colleagues showed that cyclists ingesting high amounts of carbohydrate in training—around 90 grams per hour—for 28 days showed significant increases in the number of carbohydrate transporters in the gut, for both glucose and fructose. The gut grew more transporters, which raised the ceiling for absorption.

The second is a reduction in gastrointestinal symptoms. Studies by Jeukendrup, Costa, and colleagues showed that repeated exposure to high carbohydrate loads during exertion reduced self-reported stomach distress over time, even before measurable transporter increases would explain the full effect. Part of this adaptation appears to be related to a reduction in gut sensitivity and improved gastric motility.

How Long Does It Take

Significant adaptation appears to begin within 2-4 weeks of consistent high-carbohydrate fueling in training. Cox’s study used a 28-day protocol. Research related to symptom reduction suggests improvements can be seen in as little as 7-14 days of regular practice.

This means gut training isn’t started two days before your goal race. It’s a training block gradually built over 4-8 weeks preceding a major event, systematically increasing carbohydrate intake on long runs rather than jumping to race-day rates overnight.

What Specifically to Practice

The stimulus that drives gut adaptation is high carbohydrate intake at intensities analogous to exertion. Consuming carbohydrate at rest will not produce the same adaptational response.

Practically, a minimum of 2-3 long runs per week should incorporate carbohydrate intake at your target race rate (60-90 grams per hour, or more for ultra distances). The duration of fueled sessions should progressively increase from 90 minutes to three hours and beyond as the cycle progresses. And fueling should be done at or near race intensity, because the gut adapts to specific conditions, not general exertion.

The Taste Fatigue Component

There’s an underappreciated aspect of gut training: sensory adaptation. Repeated exposure to specific flavors and textures during exertion reduces the aversion response that builds up over the course of a long race. Athletes who train exclusively with unflavored or mildly flavored fuel find taste fatigue to be a much smaller factor in a race.

Conversely, athletes who use highly flavored gels in training and race with the same product often find that the flavors they enjoyed at mile 10 become actively repulsive by mile 60. Sensory fatigue is also trainable—in the direction of minimizing it.

Summary

Gut training is real, evidence-based, and it works. The gut is an adaptive organ. It responds to the stimulus you provide it. Athletes who systematically practice high-carbohydrate fueling will arrive at their goal races with significantly greater absorption capacity, fewer symptoms, and greater confidence in their fueling plan. The cost is 4-8 weeks of consistent practice. The alternative is to wing it on race day.

References

Cox GR, Clark SA, Cox AJ, Halson SL, Hargreaves M, Hawley JA, et al. (2010). Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. Journal of Applied Physiology. 109(1), 126–134.

Jeukendrup AE. (2017). Training the gut for athletes. Sports Medicine. 47(Suppl 1), 101–110.

Costa RJS, Miall A, Khoo A, Rauch C, Snipe R, Camões-Costa V, Gibson P. (2017). Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Applied Physiology, Nutrition, and Metabolism. 42(5), 547–557.