What to eat during exercise? Carbs per hour by intensity
Gel or no gel? That's the wrong question. The right question is how much, and for what intensity.
The slower the effort, the more the body runs on fat, and the less sugar it needs. The higher the intensity, the more it draws on carbs, and the more you need to give it. Swallowing a gel every 30 minutes on an easy run makes no sense. Neither does running a marathon without any carbs.
This guide gives you our benchmarks: how many carbs per hour for each type of effort, what to drink, and how to build your fuelling strategy, from the long Zone 2 run to the ultra.
Our benchmarks: carbs per hour by intensity
Long Zone 2 run: 5 to 20 g per hour
The effort: aerobic base training, long slow distance (LSD). You can speak in full sentences.
The fuel: mostly fat. The goal of the session is to teach the body to use its own, not to drown it in sugar.
- BSE Zone 2: 1 pouch every 2 hours.
- If you want carbs, stay between 5 and 20 g per hour: half a banana is enough.
- Water, salted if it's hot.
Tempo, threshold, strength: 20 to 45 g per hour
The effort: sustained pace, threshold session, race of 1 to 3 hours (half marathon, marathon). You can only get a few words out.
The fuel: carbs take on a bigger share. You need to take them in, in small, regular amounts.
- BSE Tempo: 1 serving per hour in 500 ml of water, in small sips. 15 g of carbs and 600 mg of sodium.
- To get closer to 45 g, top up with real food: a banana provides around 25 g.
Ultra and long races: 45 to 90 g per hour
The effort: long trail runs, ultras, races lasting several hours at sustained intensity.
The fuel: mixed. Fat carries the duration, carbs carry the intensity and the climbs.
- BSE Tempo every hour for sodium and a carb foundation.
- BSE Zone 2 every 2 hours for baseline energy.
- Real food to top up: banana, salted potatoes, fruit purée, dates.
We're developing new products for these efforts. In the meantime, real food does the job very well.
| Type of effort | Carbs per hour | BSE fuel |
|---|---|---|
| Long Zone 2 run (LSD) | 5 to 20 g | Zone 2: 1 pouch every 2 h |
| Tempo, threshold, strength | 20 to 45 g | Tempo: 1 serving per hour + real food |
| Ultra, long race | 45 to 90 g | Tempo + Zone 2 + real food |
How to know which zone you're in
The simplest way is the talk test. If you can speak in full sentences, catching your breath every four or five sentences, you're in Zone 2. If you can only get a few words out, you're above your aerobic threshold, and your carb needs go up.
For a more precise benchmark, calculate your zones from your aerobic threshold in our article on the long Zone 2 run.
Drinking and salt during exercise
Carbs are only part of fuelling. On a long effort, you lose water and sodium every hour, even more so when it's hot.
- Drink regularly, in small sips, rather than large volumes at once.
- Take in sodium as soon as the effort lasts more than an hour or it's hot: one serving of Tempo provides 600 mg of sodium in 500 ml.
- Adjust for the heat: in high heat, you'll need to drink more.
Three concrete examples
- 3-hour long run in Zone 2: 1 Zone 2 pouch at the start, 1 pouch at 2 hours, water, and half a banana if you feel like it.
- Marathon in 3 h 30: 1 Zone 2 pouch 30 minutes before the start, then 1 serving of Tempo per hour in small sips and one banana per hour. You're at around 40 g of carbs per hour.
- 6-hour trail run: Tempo every hour, 1 Zone 2 pouch every 2 hours, and real food at the aid stations to get towards 45 g of carbs per hour and more on the hardest sections.
Gut tolerance is built in training
It's not the number of calories that makes fuelling work, it's your stomach's ability to absorb them after several hours of effort. That tolerance can be trained: test your strategy on your long runs, at race pace, with the products and foods you'll use on race day.
On race day, you discover nothing. You apply what you've rehearsed.
Classic mistakes during exercise
- Eating like it's race day on an easy run: gels every 30 minutes in Zone 2 stop the body from learning to use its fat.
- Taking nothing during a marathon: beyond 2 hours at a sustained pace, you need carbs.
- Waiting until you crash to eat: regular intake prevents the drop, it doesn't fix it.
- Taking everything at once: small, regular amounts are better than big doses.
- Forgetting salt: on a long effort or in hot weather, water alone isn't enough.
Conclusion: fuel the effort you're actually doing
There's no single right fuelling strategy. There's one per intensity. On a slow run, eat the way the body burns: fat, salt, very little sugar. When the intensity rises, add carbs in small, regular amounts. That's the logic that builds the engine in training and keeps it running on race day.
To go further: what to eat before a race, sports recovery: what to eat after exercise, energy gels: should you take them?, aerobic base training explained and the long Zone 2 run.