Most marathons aren't lost in the legs. They're lost in the stomach, somewhere between mile 18 and mile 22, when the carbohydrate you should have been drip-feeding for the last two hours simply isn't there. The wall is real, and it has a metabolic cause: your muscles and liver can only store around 400–500g of glycogen, which gives most runners somewhere between 90 and 120 minutes of hard effort before the tank runs low. Almost everyone running 26.2 miles will be out there longer than that, which is exactly why working out what to eat during a marathon is not a nice-to-have. It is the difference between a strong negative split and a death-march to the line.
The good news is that race-day fuelling is one of the most controllable variables in the entire sport. You can't change the weather or your training history on the start line, but you can absolutely decide how many grams of carbohydrate go in per hour, when they go in, and what form they take. This guide lays out the numbers that actually matter, the practical timing, and the mistakes that catch out even experienced club runners.
How Many Carbs You Actually Need Per Hour
The headline number for most marathoners is 60g of carbohydrate per hour. That figure isn't arbitrary; it's the ceiling for how much glucose a single transporter (SGLT1) in your gut can absorb. Go beyond it with glucose alone and the excess just sits in your stomach, drawing in water and giving you that sloshing, nauseous feeling nobody wants at mile 20.
If you're a faster runner finishing in the three-to-four-hour range, or you've deliberately trained your gut, you can push towards 80–90g per hour. The trick is using a mix of glucose and fructose, because fructose uses a different transporter (GLUT5). A roughly 2:1 glucose-to-fructose blend lets you absorb closer to 90g per hour without the GI distress. For a sub-3 runner burning through glycogen at a frightening rate, that extra 30g an hour is genuinely worth minutes.
To put it in real terms: 60g per hour over a four-hour marathon is 240g of carbohydrate. That's a lot to take on while running — in gel terms, 10 or more sachets — which is why you cannot improvise it. You need a plan with specific feeds at specific points, rehearsed in training so your gut knows what's coming.
Timing: When to Take Your Fuel
The single biggest error runners make is waiting until they feel they need fuel. By the time you feel flat, you're already 20–30 minutes behind where your blood glucose should be, and clawing that back mid-race is nearly impossible. The principle is simple: fuel early and fuel little and often.
Start taking carbohydrate within the first 30–45 minutes, while your stomach is calm and blood is still being shared generously with your digestive system. After that, aim for a small feed every 20 minutes rather than one large hit every hour. Three feeds of 20g spread across an hour are far gentler on the gut than 60g in one go, and they keep blood glucose far more stable.
Don't forget the lead-in either. A carbohydrate-rich breakfast of 1–4g per kilo of bodyweight, eaten three to four hours before the gun, tops up liver glycogen that's been depleted overnight. A 70kg runner might aim for 100–150g: porridge with banana and honey, a couple of slices of toast with jam, and a sports drink is a classic, well-tolerated combination. And the real lead-in starts two to three days earlier — see our guide to carbohydrate loading for running for the full 48-hour plan.
What to Eat During a Marathon: Choosing Your Format
When deciding what to eat during a marathon, format matters as much as the carbohydrate itself. Your three main options are gels, chews or pastilles, and drinks, and most runners end up using a combination.
Gels are concentrated and light, delivering around 20–25g of carbohydrate in a small sachet, but many runners find them cloying and they demand water to dilute them properly. Drinks combine fluid, electrolytes and carbohydrate in one, which is efficient, but you're tied to what the aid stations serve unless you carry your own. Energy chews and pastilles sit in a useful middle ground: you can take one or two at a time for precise, gentle dosing, they taste like real food rather than syrup, and they don't require as much water as a gel. The act of chewing also gives a psychological lift on a long, lonely stretch. (For the full head-to-head, see Energy Chews vs Gels.)
Whatever you choose, the golden rule is nothing new on race day. Your gut is trainable, but only if you practise. Use your long runs as dress rehearsals, taking on the exact products at the exact intervals you'll use in the race. This is also how you train those glucose transporters to absorb more, which is why a runner who has fuelled diligently in training can tolerate 90g per hour while a novice gags at 45g.
Don't Forget Hydration and Electrolytes
Carbohydrate doesn't work in isolation. On a warm day you can lose 1–1.5 litres of sweat per hour, and with it significant sodium. Aim to drink to thirst rather than forcing fluid, which can lead to the dangerous over-dilution known as hyponatraemia. As a rough guide, 400–800ml of fluid per hour suits most runners, with more in heat. Look for around 300–700mg of sodium per litre if you're a salty sweater or racing in warm conditions; you'll often see white salt marks on your kit if you fall into that camp. Pairing your carbohydrate feeds with fluid at aid stations keeps everything moving through the gut and absorbing properly.
What We Use at FTP Endurance Fuel
We built FTP Endurance Fuel because we wanted real, no-nonsense fuel we'd actually want to eat at mile 20. Our energy pastilles are designed around exactly the principles above: an optimised carbohydrate blend for fast absorption, dosed so you can take one or two at a time and hit that 60g-per-hour target without a sugary, claggy mouthful. They're easy to chew on the move, easy to stash in a race belt, and they taste of fruit, not chemicals.
For marathon training and racing, plenty of our runners reach for the Mixed Fruit Pastilles for the variety across a long effort, while the Tart Cherry Pastilles carry anthocyanins that help blunt the oxidative stress and muscle soreness that come with pounding the roads for hours. If you've not tried them before, the Taster Pack is a low-risk way to test them on a long run before you commit to race day.
Putting It All Together
A workable marathon fuelling plan looks like this: a carbohydrate-rich breakfast three to four hours out, a feed within the first 45 minutes, then small carbohydrate hits every 20 minutes targeting 60g per hour (more if you've trained for it), all washed down with fluid to thirst and topped up with sodium on warmer days. Write it on your arm if you have to. The runners who execute a plan, rather than reacting to how they feel, are the ones still moving well when everyone around them is walking.
Nail your fuelling in training, rehearse it on every long run, and the wall stops being inevitable. If you want fuel built for exactly this job, take a look at our bundles and dial in your race-day plan well before the start line.
