How many grams of carbohydrate per hour should you take in a marathon?
For most runners covering the marathon distance, the working range in sports nutrition practice is roughly 30–60 g of carbohydrate per hour from a single sugar source, rising toward 60–90 g per hour only when the drink or gel combines glucose with fructose and only after the gut has been trained to handle it. That range is guidance built on carbohydrate metabolism and coaching practice, not a number a controlled marathon feeding trial has pinned down for you personally. The honest answer is conditional: how much you can actually absorb and tolerate depends on your pace, your finishing time, and how much you have practised eating on the run.
The chemistry behind those numbers is well established. The controlled human evidence behind them is much thinner, and the gap between the two is where most fuelling advice goes wrong.
Where does the per-hour number come from?
The ceiling on carbohydrate intake during long exercise is set by absorption, not by how fast your muscles can burn fuel. Glucose crosses the gut wall through a specific transporter (called SGLT1), and that transporter saturates at around 60 g per hour. Push more glucose-only fuel past that point and the extra sugar sits in the gut, drawing in water and causing the bloating and cramping most runners recognise from over-fuelling.
Fructose uses a different transporter (GLUT5), so combining glucose and fructose lets the gut move more total carbohydrate — the basis for the 90 g per hour figure marketed on some products. That is a mechanism, and a well-established one. It explains why multi-transportable carbohydrate blends can be absorbed faster than glucose alone. It does not, on its own, prove a faster marathon.
Two things about that number deserve to be stated plainly. First, the higher end applies to sustained efforts long enough for fuel to matter — a marathon qualifies, a 10 km does not. Second, the gut adapts: transporter capacity rises when you regularly eat carbohydrate during training, which is why an untrained gut hitting 90 g per hour on race day is a common way to end a marathon in a portable toilet rather than a personal best.
Is this a question about your body or about a number on a label?
This is worth separating before you act on any figure. The 60 g and 90 g values describe how much carbohydrate the average gut can absorb per hour. They are not a prescription for how much you personally need, and they are not measurements taken from your own digestion.
Two runners can read the same 90 g per hour claim and draw opposite conclusions — one who has trained the intake and can use it, one who cannot and will only make themselves sick. The label reports absorption capacity; your race reports what your gut and your pace actually allow.
What has human research actually tested?
This is where the gap between mechanism and outcome opens up. The idea that your fuel source is a decisive lever on performance has been directly challenged. In one randomised crossover trial in recreational distance runners, tested in the fed state to control for glycogen and low blood sugar, the substrate a runner oxidised did not influence middle-distance running performance. That result concerns middle-distance running, not the marathon, and it addresses which fuel the body burns rather than how many grams per hour you should eat — but it is a useful check on the assumption that manipulating fuelling always moves the finish line.
On the marathon distance specifically, a good deal of the controlled work has looked at what you add to carbohydrate rather than how much carbohydrate to take. Adding protein to a carbohydrate drink is a common example. In one trial, adding protein to a pre-exercise carbohydrate beverage did not influence running performance or the metabolic biomarkers measured, in middle-distance runners. In a separate study of recreational runners during and after a marathon, taking carbohydrate plus protein rather than carbohydrate alone influenced some markers of post-exercise recovery — soreness, fatigue ratings and a muscle-damage marker — rather than race performance itself.
Read together, these tell you something specific: the strongest reason to fuel during a marathon is to keep carbohydrate available for a long effort, and the controlled evidence for tweaking the composition of that fuel points more at recovery than at a faster time. What no trial here has done is establish a precise optimal grams-per-hour target for a given runner over 42.2 km. That study — matched runners, several intake rates, real marathon pace, performance as the outcome — is the one that would settle the number, and the advice in circulation does not rest on it.
Does the answer change with your finishing time?
Yes, and this is where a single number misleads. A runner finishing in under three hours has a limited window to take in fuel and burns carbohydrate fast, so the upper end of the range and a trained gut can make sense. A runner out on the course for four or five hours has more time to eat but a lower carbohydrate burn rate, so the same 90 g per hour is both harder to stomach and less necessary.
The mechanism runs differently across those durations, so the sensible target does too. Faster and longer are not the same problem, and the same absorption ceiling produces different practical advice for each.
Who does this not apply cleanly to?
Individual variation here is real, not a disclaimer. Some runners tolerate high carbohydrate intake comfortably; others develop gut symptoms well below 60 g per hour no matter how they train. Body mass changes the burn rate. Fructose malabsorption, which is common, lowers the ceiling on glucose–fructose blends specifically. And the gut's absorptive capacity is trainable, so a figure that is unreachable in an untrained runner may be routine for the same runner months later.
A group average is not a promise to the individual reading it. If you get gut distress at a given intake in training, that is your ceiling for race day, whatever the label says.
What this answer does not settle
It does not give you your personal number. The per-hour ranges are absorption capacities and coaching practice, not a tested prescription for your pace and your gut. It does not tell you that hitting the top of the range will make you faster — the mechanism supports absorbing more, not automatically finishing sooner. And it does not cover fuelling for shorter races, where a well-fed runner has enough stored glycogen that per-hour intake barely matters.
The decision rule to carry into your next long run is this: the only intake that counts is the one your gut has practised at your race pace. Treat the label's grams-per-hour figure as a ceiling on what is absorbable, not a target handed to you — then find, in training, the amount below that ceiling you can actually take in without symptoms. That number, not the one on the packet, is the one to use on race day.
Sources
- Substrate Oxidation Does Not Influence Middle Distance Running Performance: A Randomized Controlled Crossover Trial (Nutrients, 2025) — used for the finding that the fuel a runner oxidised did not change middle-distance performance in the fed state.
- Adding protein to a carbohydrate pre-exercise beverage does not influence running performance and metabolism (J Sports Med Phys Fitness, 2023) — used for the null result on adding protein to a carbohydrate drink before running.
- Protein Supplementation During or Following a Marathon Run Influences Post-Exercise Recovery (Nutrients, 2018) — used for the finding that carbohydrate plus protein affected recovery markers around a marathon rather than performance.
