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How many carbs per hour do you need?
Carbohydrate is the single variable that decides whether you finish a long session strong or spend the last hour hanging on. The numbers are well established — what most athletes get wrong is the ceiling, and the spacing.
Under about an hour, you don't need to eat during exercise — your stored glycogen covers it. Between one and two and a half hours, aim for 30–60g of carbohydrate per hour. Beyond that, up to 90g per hour if your gut is trained for it. Spread it in small amounts every 15–20 minutes rather than in a few large hits.
Why there is a ceiling at all
Your body can only absorb so much carbohydrate per hour, and the limit isn't your stomach — it's the transporters in the wall of your intestine. Glucose crosses using a transporter called SGLT1, which saturates at roughly 60g per hour. Eat more glucose than that and the excess simply sits in your gut. That is where cramps, sloshing and the sensation of carrying a water balloon come from. It isn't a sign you need to push through; it's undelivered fuel.
Fructose uses a different transporter, GLUT5. Because it's a separate route, combining the two lets you absorb more in total than either alone — which is why nearly every modern sports drink and gel blends them, and why intakes up to about 90g per hour become possible. A ratio of roughly 1:0.8 glucose to fructose is what most current products aim for, and it's worth checking the label of whatever you use, because older formulations are glucose-only and will hit the 60g wall no matter how much you take.
This is the single most useful thing to understand about fuelling. Two athletes can take in identical grams per hour and have completely different experiences, purely because one is taking a glucose-fructose blend and the other is taking three glucose gels and wondering why their stomach has stopped cooperating.
How much you actually need
Intake scales with duration and intensity, not with how hard the session feels. A brutal 45-minute interval set needs no fuel during it. A comfortable four-hour ride needs a plan.
| Session length | Carbs per hour | What that looks like |
|---|---|---|
| Under 60 min | None needed | Water is enough. Your stores cover it. |
| 60–150 min | 30–60g | One or two gels an hour, or a carb drink. |
| Over 150 min | Up to 90g | Drink plus gels or chews, taken continuously. |
The upper end of that last row comes with a condition attached: 90g per hour is only achievable if you have practised it. Straight off the couch, many athletes struggle beyond 30–45g per hour before their gut protests. That tolerance is trainable, and training it is covered in its own right below.
A 60g hour in practice
Grams per hour is an abstraction until you attach it to actual food. Some combinations that land near 60g:
- Two standard energy gels (roughly 22–25g each) plus a few sips of a carb drink.
- 500ml of a 6% sports drink (about 30g) plus one gel and half a banana.
- A single-serve drink mix designed for high-carb use — several now put 60–80g in one bottle, which removes the logistics entirely.
- A bar (around 40g) plus a gel, if you can chew at your intensity.
Brand values vary more than you'd expect, so check your own labels. Two gels that look identical can differ by 10g, which over four hours is a whole extra gel's worth of error.
Spread it out
Taking your hourly target in small amounts every 15–20 minutes is far easier on the gut than one large dose, and keeps blood glucose steadier. A gel every 20 minutes beats three gels in the last half hour, even though the total is identical.
The reason is simply that the transporters work at a fixed rate. Delivering 60g in one go doesn't make them work faster; it just means most of that 60g waits in your gut for its turn, which is exactly the situation you want to avoid. Small and frequent keeps the supply line matched to the delivery rate.
The practical version of this is to set a repeating reminder rather than relying on feel. Almost nobody remembers to eat on schedule at hour three, and by the time you feel like you need something, you are already behind.
Start earlier than feels necessary
Begin fuelling within the first 20–30 minutes of a long session, before you want anything. Glycogen depletion is a slope, not a cliff, and the point of fuelling is to flatten the slope — not to rescue yourself at the bottom of it. Once you've properly run out, fast carbs help, but recovery takes 15–20 minutes and you won't get back to full pace. It's a problem solved preventatively or not at all.
What about low-carb and fat adaptation?
Training with low carbohydrate availability has a genuine place in a programme, and some athletes use it deliberately in easy sessions to nudge fat metabolism. What the evidence does not support is racing that way at intensity. Above roughly moderate effort, carbohydrate is simply the faster fuel, and no amount of adaptation changes the arithmetic of how much power fat oxidation can supply per minute. If your event involves sustained hard effort, fuel it with carbohydrate.
Putting a number on your own session
The ranges above are the framework. Where you sit inside them depends on your body mass, how long you'll be out, how hard you're going, the conditions and what your gut is used to — which is a lot of variables to hold in your head at the start of a ride.
Get your own carb target in about a minute
Enter your sport, duration, intensity and weight, and My Fuel Plan gives you carbohydrate, fluid and sodium targets per hour, plus what to actually take to hit them.
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Based on guidance from the International Society of Sports Nutrition and the American College of Sports Medicine. General information for healthy adults, not individual medical or dietary advice.