Trail runner in the mountains reviewing a nutrition strategy during a long training session.

Gut training guide

Build a genuinely tested carbohydrate capacity

A g/h target describes a strategy. It proves neither what you actually consume nor what your intestine absorbs. The aim is to learn from comparable tests without automatically climbing towards the highest value.

Scientific revision 1.0 · 31 July 2026

Understand before testing

A target, actual intake and a digestive response

These three pieces of information answer different questions. Mixing them creates false precision.

Trail runner visually connecting planned products, products actually consumed and the observed gut response while absorption remains unknown. — The plan, actual intake and perceived response are observed separately. Trailboard does not measure absorption or oxidation.

Understand before testingWhat Trailboard can genuinely learn

Confidence rises when the plan, actual intake and field feedback are all known.

Estimated need
What the plan targets. A range calculated from duration, intensity and context. It remains a starting assumption.
Actual intake
What was really consumed. The amount actually swallowed, calculated from the real duration and products used.
Absorption and use
Not measured by Trailboard. They cannot be inferred from the plan, product count or absence of symptoms.
Tested capacity
What was repeated without functional failure. A value tolerated during comparable efforts. It does not directly measure intestinal absorption.

Illustration, not protocolProgression is never automatic

Each step remains a hypothesis until repeated in a relevant context.

Current capacity45 g/h
Already repeated
Hypothesis60 g/h
Step to test
Comparable session
Controlled products and context
Observation
Maintain, retest or adjust

Observe · decide · retest

Tolerating 75 g/h does not make 75 g/h compulsory on race day. The selected target may remain lower.

This guide does not diagnose gastrointestinal disordersSymptoms determine the next step

A difficult session is not rewarded by raising the target. The next action follows the actual impact.

StableRepeat before increasing
No functional impact
To confirmKeep the step and isolate one variable
Mild or variable discomfort
Test failedReduce and do not escalate
Intake impossible or marked symptoms

The absence of symptoms is useful tolerance information. It is not a direct measure of carbohydrate absorption or oxidation.

Observe, test, decide

A four-step method

Controlled trials show that the gastrointestinal system can adapt. They do not prove that one protocol, duration or target suits every trail runner.

Two comparable trail sessions shown as an experiment with only one nutrition element changed between them. — Same route, intensity and conditions: changing one variable makes the result easier to interpret.

Establish the known point
Scientific literature
How much did you actually consume during a successful session?
First reproduce that strategy with the same products and calculate actual intake, not just planned intake.
One success is a signal, not a confirmed capacity.
Jeukendrup (2017)
Change only one variable
Field method
Are you testing rate, product, drink or context?
Change one main element. Otherwise a better or worse result remains difficult to explain.
Step size is an individual practical choice, not a consensus prescription.
Repeat in a comparable context
Controlled trials
Does the result hold with similar duration, intensity and terrain?
Repeat the step before calling it tested. Record heat, elevation, pace, drink volume and products.
Controlled studies support gut adaptability, but their small samples cannot promise an individual outcome.
Costa et al. (2017) Miall et al. (2018)
Run a race-specific rehearsal
Consensus and literature
Is the strategy still usable when terrain complicates intake?
Test carried products, portions, climbs, descents, heat or darkness that resemble race day.
A value becomes a race candidate after repeated use without limiting symptoms in a relevant context.
Burke et al. (2019) Jeukendrup (2017)

Do not increase after an ambiguous test. Repeating the same step produces more useful information than immediately adding grams.

Illustration, not protocol

From 45 to 60, then possibly 75 g/h

This example shows a decision logic. It sets neither a mandatory number of sessions nor a universal calendar.

Trail runner moving through nutrition steps with repetition loops and a higher step shown as an option rather than a finish line. — A step may be repeated, maintained or abandoned. The highest value is never a compulsory destination.

Assumption: 45 g/h has already been genuinely consumed and well tolerated during a long session.

45 g/hKnown

Current reference

Recalculate products actually consumed and check that the value holds across several sessions.

60 g/hTo validate

Candidate step

Test with one main change, then repeat in a comparable session before changing the target.

75 g/hNot required

Conditional option

Consider only if the race justifies it, 60 g/h is stable and the carbohydrate mix and products are prepared.

Race-required capacity and athlete-tested capacity must remain visible separately. Trailboard can propose closing the gap, never manufacture validation.

Mountain specificity

Terrain changes feasibility, not only need

These tactics are mainly field practice. They must be tested with the same products and constraints as the race.

Steep climb

Intensity and breathing can reduce comfort and make chewing difficult.

Compare intake before the climb with small intakes during a steady climb.

Technical descent

Chewing, opening packaging or drinking may become impractical.

Test format and timing without turning the descent into a laboratory.

Heat

Heat stress and dehydration may intensify gastrointestinal disturbance.

Progressively reproduce conditions and track carbohydrate, fluid and symptoms together.

Night and sweet fatigue

Fatigue, cold and monotony can make a theoretical plan unusable.

Plan and test several textures and flavours, including a simple fallback.

Turn feedback into useful data

What to record after each test

A short, consistent log is more useful than a perfect report completed only once.

Actual intake: Products finished, total carbohydrate and real test duration.
Context: Intensity, duration, elevation, heat, cold and technical sections.
Fluid: Actual volume, known concentration and associated intake.
Symptoms: Type, timing, severity and impact on the ability to keep eating or running.
Decision: Repeat, simplify, reduce or test a new step.

Trailboard

This guide does not diagnose gastrointestinal disorders

Repeated vomiting, significant diarrhoea, marked pain, blood in stool, faintness, inability to drink or recurrent symptoms justify stopping escalation and seeking medical or sports-dietitian advice.

A failed test is not a sporting failure. It is a limit of the protocol tested on that day, with those products and conditions.

Scientific references

What supports the method, and what remains uncertain

Consensus statements frame intake. Trials and reviews support gut adaptability, with sample sizes and settings that require caution for an individual ultra-trail athlete.