Key takeaways
- Use your expected running time, not just the 21.1 km distance, to guide intake.
- Count carbohydrate from drinks and foods together.
- Choose an amount practised in training and avoid forcing fluids.
Why your finish time changes the guidance
A half-marathon can mean an effort close to one hour or an outing lasting more than three. A single recommendation expressed as a number of gels misses that difference. Estimate your duration from recent training and the course profile. Remember that heat or a difficult route may also change your pace and time on your feet.
Common guidance places carbohydrate intake at 30–60 grams per hour for exercise lasting 1–2.5 hours. For a very short, high-intensity race, small amounts may be enough. These ranges describe exercise situations; they are not identical prescriptions for everyone taking part in the event.[1][2]
How should you count carbohydrate?
Add up what you actually consume: gels, carbohydrate drinks and any food. Compare values per serving rather than per 100 grams. For a drink, check the concentration after mixing and the volume you drink. A cup handed out on the course may not match the serving described on the product packaging.
Do not translate an hourly range into one universal number of sachets. Serving sizes differ between products, and a sports drink can supply a meaningful share of your carbohydrate. If you do not know its composition, its contribution remains uncertain. Check the organiser’s information before relying on it, or choose an option with quantities you understand.
How do drinks and fuel work together?
Check where the water stations are, how far apart they are and what they provide. Adapt drinking to thirst, conditions and what you have observed in training. Because sweat losses vary between individuals, one fixed number of millilitres per hour cannot suit the whole field.[3][4]
Avoid drinking extra fluid solely to reach a carbohydrate number. If your fluid needs and fuel choices do not match, reconsider their balance before race day. Equally, do not limit your opportunities to drink because you have already taken your carbohydrate. Energy intake and hydration remain separate questions even when a single drink contributes to both.
How can you protect digestive comfort?
Test formats, quantities and combinations in representative training sessions. Tolerating one serving does not guarantee that repeated servings alongside a concentrated drink will feel the same. Gut training is a gradual process; a sudden increase on race day is not a substitute for that preparation.[5][2]
Check practical details too: pockets should be accessible and packaging easy to open. Spread intake rather than swallowing everything at the final station. Keep your approach simple enough to use when tired. An intake you can tolerate is more useful than a theoretical maximum you first attempt on the start line.
Match intake to expected duration
| Expected duration | Carbohydrate guidance | How to use it |
|---|---|---|
| Around 1 hour | Small amounts may help | A short, high-intensity race context. |
| 1–2.5 hours | 30–60 g/h | Count food and drinks together; practise your target. |
| Beyond 2.5–3 hours | Individualise intake | Start from an intake you tolerate; duration alone does not justify increasing it. |
The boundaries are approximate, and 60 g/h is not a target to reach at any cost. A longer half-marathon does not justify aiming for 90 g/h: this high intake is not a standard guideline for this distance. Prioritise an amount tolerated across several training sessions.[2][1]
Frequently asked questions
Can a sports drink replace gels?
It can supply some or all of your planned carbohydrate if its concentration and the volume consumed allow it. Check that this also fits your fluid needs and digestive comfort. There is no need to combine both formats simply for the sake of it.
Should I wait until I feel hungry to fuel?
It is better to think about intake before starting than to depend only on hunger during the race. This does not require a rigid timetable: use your training experience and the actual opportunities to get fuel on the course.
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.
- Australian Institute of Sport — Sports gels: how and when do I use it?
- Jeukendrup — A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise (2014).
- 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).
