Marathon fuelling comes down to one number: how much carbohydrate you can absorb and use per hour. Everything else - gel flavour, aid station choice, bottle setup - orbits around it.
The honest answer varies by finish time, gut training and race conditions. This guide gives you realistic per-hour targets, the reason running motility caps intake lower than cycling, and a rehearseable protocol to get there without a portaloo stop.
Carbs per hour by marathon finish time
| Finish Time | Carb Target | Typical Delivery |
|---|---|---|
| Sub 2:30 (elite) | 90-110g/hr | Concentrated bottles at team stations |
| 2:30 - 3:00 | 80-100g/hr | Handheld flask + aid station tops-up |
| 3:00 - 3:30 | 70-90g/hr | Handheld flask, sipped every 3-4km |
| 3:30 - 4:00 | 60-80g/hr | Dilute drink mix at aid stations from 30 min |
| 4:00 - 5:00 | 50-70g/hr | Regular small sips of a dilute drink mix |
| 5:00+ | 40-60g/hr | Small, frequent sips throughout |
Why running caps intake lower than cycling
Cyclists routinely take 90 to 120g of carbohydrate per hour on the bike. Runners typically cap out around 90g/hr - and most cap much lower. The reason is mechanical: running impact slows gastric motility. The rhythmic pounding of foot strike reduces the rate at which the stomach empties into the small intestine, where absorption happens.
Practical implication: the intestinal transporters (SGLT1 for glucose and GLUT5 for fructose) can handle the carb load, but the stomach is often the bottleneck on the run. This is why fuelling in small, frequent doses beats large gulps for runners, and why isotonic formulations (like HYDRAX CORE) empty faster than hypertonic ones. See why osmolality matters for endurance nutrition.
The physiology of dual-carb fuelling
A single carbohydrate source (glucose or maltodextrin) saturates the SGLT1 intestinal transporter at around 60g per hour. Above that, extra glucose just sits in the gut, drawing water in and causing GI distress.
Adding fructose activates GLUT5, a separate transporter that works in parallel to SGLT1, lifting total absorption capacity to 90 to 120g per hour (Jentjens & Jeukendrup, 2005). This is why HYDRAX CORE is formulated at a 2:1 maltodextrin-to-fructose ratio - the peer-reviewed sweet spot for maximal exogenous carbohydrate oxidation. Deep dive in why dual-carbohydrate transporters matter.
Dual-carb, high-sodium endurance fuel. Built for the marathon distance.
Shop HYDRAX COREHow to build up to 60 to 90g/hr on the run
The gut adapts to what it is exposed to. Runners who cannot tolerate 60g/hr today can typically be comfortable at 90g/hr after 6 to 8 weeks of structured practice on long runs.
Rehearsal target: practice your race-day fuel plan on at least 3 long runs at race pace before race day. If you have not taken 60g/hr on a long run, do not attempt it on race day.
Full protocol in gut training for endurance fuelling.
Sodium during a marathon
Cramps in the last 8km of a marathon are almost always sodium, not carbs. Target 300 to 800mg of sodium per hour depending on sweat rate and conditions. HYDRAX CORE delivers 980mg per serve, so even at moderate volumes you cover most sodium needs.
Estimate your losses with the sweat rate estimator, and read the full guide on how much sodium endurance athletes actually need.
Practical marathon fuel protocol
| Timing | Action |
|---|---|
| 25-40 min pre-race | 1 serve HYDRAX PRIMER in 400-500ml water |
| 0-30 min | Water only if desired; the pre-race PRIMER is doing its work |
| 30 min-halfway | Small sips of CORE every 3-4km from handheld flask |
| Halfway-32km | Maintain rhythm; do not let intake gap open up |
| 32km-finish | Reduce concentration if gut is tight, but keep taking sodium and fluid |
Dual-carb, high-sodium endurance fuel. Built for the marathon distance.
Shop HYDRAX COREBuild your own per-hour plan
Finish-time bands are a starting point, not a prescription. Your real ceiling depends on body weight, heat, gut training and pacing strategy. Use the tools below to calibrate to your race, then rehearse on long runs before you trust it on race day.
- HYDRAX Fuelling Strategy Engine - generate a per-hour plan from your weight, goal time and conditions.
- Sweat rate estimator - lock in your sodium and fluid targets.
- Running pace calculator - align pace, split time and fuel timing.
Related reading
- Complete marathon fuelling plan
- Carbs per hour cycling
- Carbs per hour for Ironman-distance events
- Carb loading before race day
- Endurance fuel for runners
Frequently Asked Questions
How many carbs per hour should a marathon runner take?
For sub-3 runners, target 80 to 100g/hr with a dual-carb formulation and a rehearsed gut. For 3 to 4 hour finishers, 60 to 90g/hr is realistic. For 4-plus hour finishers, 50 to 70g/hr is a good working range. These are starting points, not prescriptions - calibrate with the HYDRAX Fuelling Strategy Engine and rehearse on long runs.
Is 90g of carbs per hour realistic on a marathon?
For trained runners with a rehearsed gut and a dual-carb drink mix, yes. Running motility is lower than cycling motility, so most runners cap around 100g/hr rather than the 120g/hr+ possible on the bike. Do not attempt 90g/hr on race day without training it first.
When should I start fuelling in a marathon?
Start by the 30 to 40 minute mark, before you feel low. Small, regular sips of a dual-carb drink mix keep blood glucose stable through the second half. Reactive fuelling almost always leads to hitting the wall.
Gels or drink mix for a marathon?
A dilute dual-carb drink mix such as HYDRAX CORE is generally gentler on the gut than a chain of gels, delivers sodium alongside carbs, and produces a smoother blood glucose profile. Many athletes combine both. See the drink mix vs gels comparison for the full breakdown.
How do I set my own per-hour target?
Use the HYDRAX Fuelling Strategy Engine to generate a plan from your weight, goal time and conditions, dial sodium with the sweat rate estimator, and rehearse the intake on your long runs. Adjust with your coach or sports dietitian based on how the sessions land.