Can you train your gut to absorb more carbohydrate?
Yes. Intestinal transporter expression and gut tolerance both respond to habitual carbohydrate intake, so practising race fuelling in training raises the rate you can handle on race day.
Absorption capacity is not fixed. Consistently taking carbohydrate during long runs increases the expression of intestinal transporters and improves gastric emptying and general tolerance, and the effect shows up over weeks rather than months. A runner who has never taken a gel in training and attempts 90 g/hr on race day is running an experiment with a predictable outcome.
The method is unglamorous: use your long runs and marathon-pace sessions as fuelling rehearsals, with the exact products, concentrations and timing you intend to race with. Start near 60 g/hr and step up by roughly 10–15 g/hr every couple of weeks, only once the current rate is comfortable.
Two details make a large difference. Take carbohydrate with enough water — concentrated sugar without fluid is the fastest route to gut trouble. And fuel from early in the session rather than waiting for hunger, because absorption slows as intensity and fatigue rise, and the goal is to keep a steady stream arriving rather than to rescue a deficit.
Key numbers
| Sensible start | 60 g/hr | in long runs |
|---|---|---|
| Progression | +10–15 g/hr | every 2 weeks, if comfortable |
| Realistic ceiling | 90–120 g/hr | after weeks of practice |
Work it out for yourself
Marathon training plan generator — Build a plan whose long runs give you the fuelling rehearsals you need.
Frequently asked questions
How long does gut training take?
Meaningful improvement in tolerance shows up over a few weeks of consistent practice. Build it into a marathon block from the start rather than trying to add it in the final fortnight, when your long runs are already tapering away.
Should you practise fuelling on every run?
No. Long runs and race-pace sessions are the right places, because they are the ones that rehearse race conditions. Adding carbohydrate to short easy runs adds calories without adding a useful stimulus.
Sources
- Jeukendrup (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine.
- Jeukendrup (2011). Nutrition for endurance sports. Journal of Sports Sciences.
Related explainers
Glossary: SGLT1, GI Distress