Under an hour you need nothing. After that, the limit is what your gut can absorb: why 60 g per hour is the ceiling and how you get to 90.
The short answer: for up to about an hour of exercise you need nothing at all. After that, refuelling becomes a topic; beyond two hours it decides the second half of your session. Those time markers are coaching practice, not study numbers — the hard limit sits elsewhere.
It sits in your gut. A single type of carbohydrate is used at a maximum of around 60 g per hour [1]: the transporter that carries glucose through the gut wall is simply occupied at that point. Anything you pour in on top never reaches the muscle — it sloshes around in your stomach and takes revenge on the next climb.
The way out is elegant: two types of sugar at once. Glucose and fructose take different routes through the gut wall. Combined at roughly 2:1, that makes up to 90 g per hour a recommendation for ultra distances; measured oxidation rates go as high as 105 g per hour [1].
To make the number tangible: 60 g of carbohydrate is roughly two to three gels — or a large banana plus a gel plus half a litre of sports drink. Per hour. In hour four it feels like homework. Which is exactly why the most important part of this guide is not the number, but the practice.
The staging by duration is coaching practice, with no scientific cloak:
Two things shift those markers: intensity and what you ate beforehand. An easy base run on a full tank carries longer than intervals after a day at the desk. The clock is a guideline; your head in hour three is the truth.
The upper limit is documented and it is unforgiving: with only one type of sugar, around 60 g per hour is the end of it [1]. More is not absorbed, it just sits there.
In practice that means:
Start low. Try 90 g on your first attempt and the main thing you will learn that day is what the roadside bushes look like.
Picture your gut wall as a supermarket checkout. Glucose has its own till, and it is fully booked at around 60 g per hour [1]. Fructose uses a second till next to it, which is still free. Open both and more gets through — hence the recommendation of up to 90 g per hour and the measured oxidation rates of up to 105 g per hour [1].
You do not need exotic shopping for this. Most modern gels and powders advertise exactly that ratio, often printed as "2:1" on the packet. And ordinary table sugar is half glucose and half fructose anyway — so it brings both routes into play, even if not at the 2:1 ratio that was studied.
All three deliver the same thing: carbohydrate. The difference is how well they sit with you at high intensity.
Rule from practice: the harder the effort, the more liquid the calorie.
Your stomach is an organ, not a fate. Never eat under load and you will tolerate nothing under load — practise regularly and you will tolerate considerably more over time. That is not a study number, it is the experience of just about every endurance coach.
Here is how: once a week, in the long easy session, eat and drink exactly what you plan to use in the race. Same brand, same amount, same intervals. Three to four weeks are enough for a noticeable difference.
A number that gets misused constantly: for rapid restoration of glycogen stores, 1.0 to 1.2 g of carbohydrate per kilogram of body weight per hour as early as possible makes sense [2]. At 75 kg that is around 80 g per hour — two large bananas plus a roll with honey.
But: that applies to a second session in under eight hours [2]. Training camp, tournament day, double session. If you are not training again until tomorrow you have 24 hours, and then all that counts is what adds up across the day.
This guide explains training practice and does not replace medical or dietetic advice. If you have diabetes, take blood-sugar medication, live with a gastrointestinal condition such as IBS or coeliac disease, or are pregnant: discuss your fuelling with a professional first. The numbers above come from sports nutrition for healthy athletes.
Persistent gastrointestinal trouble under load is not a sign of weakness, it is a signal. If cramps, nausea or diarrhoea keep showing up, that belongs in a consulting room — not gritted through.
And the limit in the other direction: fuelling does not replace drinking. Eat for hours but drink too little and you will still slow down. Drink too much out of fear of that, and you risk something more serious. Both are in the next guide.
Split your hourly ration into three portions every 20 minutes — and start within the first 30 minutes, while your stomach is still calm and you do not have to force anything. Small amounts at short intervals are almost always easier to tolerate than one big hit every 60 minutes.
The second trick applies to anything with climbs: take the portion before the hill, not halfway up it. At high intensity your stomach largely stops working. Whatever you force in at the summit is still sitting there when things get fast again on the descent.
Up to about 60 to 75 minutes water is enough — your stored muscle glycogen covers it. Between one and two and a half hours refuelling starts to matter, and from around three hours it decides your pace. These time markers are experience values; how fast your tank empties depends on intensity and on your last meal.
With only one type of sugar, the absorption ceiling is reached at around 60 g per hour [1]. For sessions up to two and a half hours, 30 to 60 g is plenty. For ultra distances up to 90 g per hour is recommended — but only if glucose and fructose are combined at roughly 2:1 [1].
For your body they are the same; for your stomach they are not. The harder the effort, the more liquid the calorie should be. A sports drink solves hydration and fuelling at once and is the best entry point. Gels need water afterwards; solid food needs calm stretches for chewing.
Only if the next hard session is less than eight hours away — then 1.0 to 1.2 g per kilogram of body weight per hour as early as possible makes sense [2]. With 24 hours in between, sprinting to the shaker changes nothing. Then only the daily total counts.
How Much Do You Really Need to Drink During Sport?