Gut Training for Triathlon: How to Build High-Carb Fuelling Tolerance

If you’ve read anything about long-course fuelling recently, you’ve probably seen the numbers climbing — pro athletes reportedly taking on 100g or more of carbohydrate per hour, well above the 60g/hour ceiling that was standard advice for years. The gap between “what elites do” and “what you should do” comes down to one thing: gut training. Here’s what it actually is and how to build it into your own programme without wrecking a session with GI distress.

Why the Old 60g/Hour Advice Is Outdated

The old ceiling came from research on glucose-only fuelling, where a single transporter in the gut (SGLT1) limits how much carbohydrate you can absorb per hour regardless of how much you eat. Modern sports nutrition products combine glucose and fructose, which use two separate gut transporters at once, raising the practical absorption ceiling to 90g/hour or more for a trained gut — and, per current guidance, up to 90-150g/hour for very well-adapted athletes. The catch is the word “trained”: your gut doesn’t do this automatically, and pushing intake up faster than it can adapt is one of the best-documented causes of race-day GI problems and DNFs.

How Gut Training Actually Works

Like muscles adapting to a training load, the gut’s carbohydrate transporters and gastric emptying rate adapt to repeated, progressive exposure to higher carb intake during exercise. The training principle is the same as any other adaptation: consistent, gradually increasing stimulus, not a single big test a week before your race.

Building It Into Your Week

Frequency: practice fuelling at your target intake in at least 2-3 sessions per week, not just your longest weekend ride
Start early: begin fuelling within the first 15-20 minutes of the session, rather than waiting until you feel like you need it
Progress gradually: if you’re currently comfortable at 60g/hour, don’t jump to 90g/hour in one session — step up by roughly 10-15g/hour every week or two
Use a glucose-fructose blend: products listing both (rather than glucose/maltodextrin alone) support the higher absorption rates this approach is built around
Rehearse race-day products specifically: gut training only transfers to race day if you’re training with the exact gels, drink mix and solid food you plan to use, not whatever’s convenient in training

Signs You’re Pushing Too Fast

Bloating, sloshing, nausea or the urge to stop and use a portable toilet mid-session are all signs your gut hasn’t caught up with your intake target yet. Drop back to your last comfortable intake level for a week or two before trying to progress again — there’s no reward for rushing this, and a bad gut-training session teaches you nothing except to fear your race-day fuelling plan.

Try our paired Gut Training Ride: Progressive High-Carb Intake Session to put this into practice on your next long ride.

This isn’t medical advice — if you have a diagnosed digestive condition, check with a doctor or dietitian before deliberately increasing race-day carbohydrate intake.