We’re in the middle of a great running season, and I’ve been supporting lots of runners racing distances from 5k to Ultra-endurance events. Most marathon and ultra runners know they should be fuelling, although the plan often needs thought. But for runners racing 5km to half marathon distance one of the most common questions I get asked is:
“Do I actually need to be fuelling?”
The answer doesn’t just depend on duration – intensity matters too. The harder you run, the more carbohydrate you use. The catch? Carbohydrate stores are limited – typically around 60–90 minutes of moderate-intensity exercise, and less if you’re underfuelled or working harder.
5k Fuelling
Most runners won’t need carbohydrate during a 5k.
A 5k is typically run at a high intensity, so carbohydrate demands are high, but you’re unlikely to deplete stores during the race itself. For most runners, nutrition before the race will have a bigger impact on performance than nutrition during it.
For early morning races, a high-carbohydrate, easily digested breakfast or snack such as a bagel with jam or honey, a banana or low-fibre cereal is ideal. Top tip: bagels contain more carbs than bread or toast, and fruit juice can help top up stores.
For later day or evening races, focus on topping up carbohydrate stores throughout the day with regular meals and snacks. Aim to arrive fuelled, but not overly full. Think easy-to-digest carbs and finish eating solids 1-2 hours pre-race.
In-race, carbohydrate mouth rinsing (swilling a sports drink around the mouth) provides a small performance benefit via receptors in the mouth signalling the brain.
10k Fuelling
For many runners, completing a 10k without taking fuel is achievable. However, because a 10k is typically raced at a relatively high intensity, carbohydrate demands remain high, so taking on some fuel could help you push harder for longer.
Taking a gel shortly before the start – and for some runners, during the race – may improve performance, particularly if the race is likely to take an hour or longer or you’re aiming for a personal best.
Psychologically, fuelling can also provide a useful mental boost when things start getting uncomfortable.
Tolerance can be a challenge at 10k intensity, so practise before race day.
Half Marathon Fuelling
The half marathon is where a fuelling strategy becomes essential.
Pre-race, we want to start with full carbohydrate stores. Aim for around 1–2g/kg bodyweight of carbohydrate for breakfast, such as a bagel with jam, a banana and a glass of fruit juice, or a bowl of cereal with milk, toast and fruit. Eat this at least 2 hours before the start.
During the race, carbohydrate can help maintain pace and offset late-race fade.
As a starting point, I’d suggest a gel around 30–45 minutes before the start, then another every 30–40 minutes during the race. If gels aren’t your thing, sports chews or a carbohydrate drink can work just as well.
One of the biggest mistakes I see is runners spending months perfecting their training plan but little time thinking about how they’ll fuel it.
Try this for your next 5k, 10k or Half Marathon
- 5k: Practise a pre-race breakfast or late-day snack strategy.
- 10k: Test whether a pre-race gel – and potentially a mid-race gel – helps you push harder to the finish.
- Half Marathon: Implement your fuelling strategy in long runs – think pre-, during and post-run.
- Whatever the distance: Don’t leave nutrition until race week.
Frequently Asked Questions
Do I need to eat or drink anything during a 5k race?
Most runners don’t need carbohydrate during a 5k. It’s short enough that you’re unlikely to deplete your carb stores before crossing the finish line. Pre-race nutrition matters far more than anything you’d take mid-race, though rinsing your mouth with a sports drink can give a small mental/performance edge.
Should I take a gel for a 10k?
It’s optional but can help, especially if you’re aiming for a personal best or expect to be racing for an hour or more. A gel shortly before the start is a good starting point, with a gel during the race being useful for some runners. Just make sure you’ve practised with it beforehand, since tolerance can be tricky at 10k intensity.
What should I eat before a half marathon?
Aim for around 1–2g of carbohydrate per kg of bodyweight at breakfast, eaten at least 2 hours before the start. Good options include a bagel with jam, a banana and fruit juice, or cereal with milk, toast and fruit.
Do I need to fuel during a half marathon?
Yes — this is where a fuelling strategy really matters. Carbohydrate during the race helps maintain your pace and reduce late-race fade. A good starting point is a gel 30–45 minutes before the start, then another every 30–40 minutes during the race.
What about later-day or evening races?
Focus on topping up carbohydrate throughout the day with regular meals and snacks. Aim to arrive fuelled but not overly full, sticking to easy-to-digest carbs and finishing solid food 1–2 hours before the race.
Why does intensity matter as well as duration?
The harder you run, the more carbohydrate your body burns through. Since carb stores are limited (roughly 60–90 minutes’ worth at moderate intensity, less if you’re underfuelled or working hard), high-intensity efforts like a 5k or 10k burn through stores faster relative to their length, even though the race itself might be short.
What should I eat before an early morning race?
A high-carb, easily digestible breakfast or snack — think a bagel with jam or honey, a banana, or low-fibre cereal. Fruit juice can also help top up your stores.
Is it worth seeing a sports dietitian for fuelling a 5k, 10k, or half marathon?
Absolutely — and it’s not just for elite runners or ultra-distance events. Even at 5k and 10k, a dietitian can help you dial in the small details that generic advice can’t cover: how your specific gut tolerates different products, what your ideal pre-race meal timing looks like based on your training schedule, or how to manage race-day nerves that affect appetite. For half marathon runners, the value goes up further, since fuelling strategy becomes essential rather than optional, and getting it wrong (or leaving it untested) can undo months of training. A sports dietitian can also help troubleshoot issues like GI distress, work fuelling around specific dietary needs or health conditions, and build a plan that’s tailored to you rather than a one-size-fits-all guideline. Ultimately, general guidance is a good starting point, but personalised support is where a lot of runners unlock the marginal gains they’ve been missing.
Author Bio
Rachel Howarth is a Registered Dietitian, Sports Nutritionist and runner based in Northumberland. Through RJ Performance Nutrition, she supports runners and endurance athletes with practical, evidence-based nutrition to improve performance, recovery and long-term health. Rachel has a particular interest in endurance nutrition, REDs and low energy availability, female athlete health, and nutrition to support injury recovery and rehabilitation. She sees clients locally in Ponteland and virtually from further afield.