Key takeaways
- Prepare intake around your expected duration and your training experience.
- 90 g/h is a high intake, not a default target: prioritise your tolerance.
- Consider fluid and carbohydrate needs separately, even when using a sports drink.
Start with your duration and the course
Two runners covering 42.195 kilometres can spend very different amounts of time outside. Estimate your likely duration, then check the route and aid stations: spacing, products available and opportunities to carry your own supplies. This turns a general intention to fuel well into workable choices without imposing a minute-by-minute schedule.
Finishing later means managing intake for longer, but it does not automatically mean needing more carbohydrate each hour. Absolute exercise intensity and tolerance also matter. If you expect to walk some sections, keep a strategy suited to that actual effort instead of copying an athlete who runs substantially faster.[1]
How much carbohydrate should you aim for?
Start with the amount you tolerate in training. The 30–60 g/h guidance applies to exercise lasting around 1–2.5 hours; beyond 2.5–3 hours, recommendations discuss up to 90 g/h in certain contexts. This high figure is not a standard target for every marathon runner. Considering it calls for gradual progression and repeated trials in conditions similar to the race, with no guarantee of tolerance.[2][1]
At higher intakes, combining glucose and fructose sources allows different absorption pathways to contribute. That does not guarantee freedom from digestive discomfort. Count carbohydrate from every source, including drinks, and check the servings you actually consume. Do not confuse a gel’s total weight with its carbohydrate content, or the amount carried with the amount swallowed.[1]
Separate water, sodium and energy
Weather, sweat losses and access to stations change your fluid needs. Use training observations and thirst to adjust drinking, rather than trying to drink as much as possible. Hydration recommendations emphasise individual differences; understanding the risks of excessive drinking is particularly relevant during long events.[3][4]
Sodium in a drink does not make overdrinking safe. Likewise, increasing fluid volume just to reach a carbohydrate target may be inappropriate. Plan how you could separate those needs if conditions change. Knowing a drink’s concentration helps, but it only becomes an actual intake when combined with the volume you really consume.[4]
Prepare an approach you can sustain
Rehearse your choices in representative sessions and increase intake gradually if needed. Test the combination of products, drink, carrying equipment and intended running intensity. Gut training can help, but tolerance remains individual and depends on conditions: a cool training day does not perfectly reproduce a hot race.[5]
Begin taking fuel regularly in line with your preparation rather than waiting for severe fatigue and trying to catch up all at once. If you miss a serving, avoid improvising a double portion. Have a familiar alternative when an advertised product is unavailable, and check gel directions about water. Simplicity makes execution easier as concentration fades.
Guidelines, not one target for everyone
| Exercise context | Carbohydrate guidance | Conditions |
|---|---|---|
| Around 1–2.5 hours | 30–60 g/h | General endurance guidance; distance alone is insufficient. |
| Prolonged exercise, with preparation for high intakes | Up to 90 g/h in certain cases | Consider only after successful gradual trials; not a standard target. |
| Intake above 60 g/h | Combined sources | Glucose and fructose, practised gradually in training. |
Duration alone does not justify aiming for 90 g/h. Even with a glucose-fructose blend and gut training, this intake may be poorly tolerated. Keep to an amount you have practised; prepare any increase gradually before race day, without pushing through digestive discomfort.[2][1]
Frequently asked questions
Do I have to reach 90 g/h?
No. This is a high intake that does not suit every runner and is not a requirement for finishing a marathon. Choose an amount repeatedly tolerated in training. Do not aim for 90 g/h in a race without successful trials.
Can nutrition alone prevent hitting the wall?
No. Intake contributes to energy availability, but pacing, training, starting fuel stores and conditions also matter. No product or hourly carbohydrate number guarantees that you will avoid a major drop in pace.
Scientific sources
These references support the guidance presented. Applying it depends on duration, intensity and your tolerance; the references do not validate Glyk’s scoring rubric.
- Jeukendrup — A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise (2014).
- Australian Institute of Sport — Sports gels: how and when do I use it?
- Sawka et al. — ACSM position stand: Exercise and fluid replacement (2007).
- Hew-Butler et al. — International Exercise-Associated Hyponatremia Consensus (2015).
- Costa et al. — Sports Dietitians Australia–USSF position statement on exercise-associated gastrointestinal symptoms (2025).
