Every runner remembers the first time a long run fell apart. Mine was mile 14 of a 16-miler: legs like wet sand, pace drifting backwards, and that peculiar hollow feeling that no amount of willpower fixes. It wasn't fitness that failed — it was fuel. Once a run stretches past 90 minutes, what you carry in your pockets matters almost as much as the training in your legs.
The good news is that finding the best fuel for long runs is not complicated. The sports science is well established, the numbers are specific, and once you've practised the routine a few times it becomes as automatic as lacing your shoes. This guide covers what to carry, how much to take, and exactly when to take it.
Quick answer: the best fuel for long runs is a glucose-fructose carbohydrate source you can drip-feed in small doses — chews, pastilles or gels taken to a schedule. On any run over 90 minutes, aim for 30–60g of carbs per hour (up to 90g for marathon-specific sessions with a trained gut), taking your first fuel 30–40 minutes in and 15–20g every 20–25 minutes after that.
Why Long Runs Demand a Fuelling Plan
Your body stores roughly 400–500g of glycogen across your muscles and liver — about 1,600–2,000 kcal of readily available energy. At a steady long-run effort, most runners burn 600–900 kcal per hour, with somewhere between 60% and 80% of that coming from carbohydrate depending on pace and fitness. Do the arithmetic and the problem is obvious: unfuelled, your glycogen tank starts running seriously low somewhere between 90 minutes and two hours.
When glycogen runs out, your body shifts to burning predominantly fat, which can only support around 50–60% of your aerobic capacity. That's the bonk — the sudden, dramatic slowdown that feels like someone pulled your plug. Crucially, once you've hit it, you cannot eat your way back quickly; digestion under stress is slow, and the damage to your session is done. The entire point of in-run fuelling is to start early and stay ahead, sparing stored glycogen rather than trying to replace it after the fact.
The Best Fuel for Long Runs: The Numbers That Matter
For runs of 60–90 minutes, most runners can get away with water and perhaps a small top-up. Beyond 90 minutes, the research-backed target is 30–60g of carbohydrate per hour. For very long sessions — marathon-specific long runs of 2.5 hours or more — well-trained guts can absorb up to 90g per hour, provided the carbohydrate comes from a blend of glucose and fructose.
That blend matters because glucose and fructose use different transporters in the gut. Glucose absorption via the SGLT1 transporter caps out at roughly 60g per hour; add fructose, which uses the separate GLUT5 pathway, and total absorption climbs meaningfully higher. A product built on a glucose–fructose blend therefore delivers more usable energy with less risk of the sloshing, bloated stomach that comes from overloading a single pathway.
A practical starting point for most runners: aim for 40–50g per hour on any run over 90 minutes, then adjust up or down based on how your stomach responds. Heavier and faster runners generally need the upper end; lighter runners at easy pace can sit lower.
| Run duration | Carb target | What to carry |
| Under 60–90 minutes | Usually none needed | Water, perhaps a small top-up |
| 90 minutes – 2.5 hours | 30–60g per hour (40–50g is a good starting point) | Chews or pastilles drip-fed every 20–25 minutes; 2 FTP pastilles ≈ 30g carbs |
| Over 2.5 hours (marathon-specific) | Up to 90g per hour with a trained gut | A glucose–fructose blend, plus electrolytes in warm conditions |
| After the run | Carbs plus 20–25g protein within 30–60 minutes | A proper recovery meal or shake to restart glycogen resynthesis |
What to Carry: Comparing Your Options
The best fuel for long runs is the fuel you'll actually take on schedule, so palatability and practicality count as much as the label. The main options:
- Energy chews and pastilles — easy to portion (one or two at a time rather than a whole sachet in one go), gentle on the stomach, no sticky mess, and they force you to chew, which stimulates saliva and starts digestion. Excellent for steady drip-feeding.
- Gels — fast and compact, but many runners find repeated gels sit heavily after the third or fourth, and most need to be taken with water to avoid gut trouble.
- Sports drinks — useful for combined fuel and hydration, but carrying enough liquid for 20+ miles is impractical without a vest.
- Real food — bananas, dried fruit and rice bars work well at easier paces, but chewing and digesting solid food above threshold effort is a gamble.
Whatever you choose, the golden rule is: nothing new on race day. Your gut is trainable, and it adapts to what you practise with. Use your weekly long run to rehearse the exact products, quantities and timings you plan to race with.
When to Take It: A Simple Timing Framework
Most fuelling failures are timing failures. Runners wait until they feel tired — but by then glycogen is already critically low. Work to the clock instead:
- 2–3 hours before: a carbohydrate-based meal of 1–2g of carbs per kg of body weight — porridge, toast and jam, rice. Nothing high-fibre or high-fat.
- 30–40 minutes in: take your first fuel. It feels absurdly early. That's the point — you're sparing glycogen, not rescuing it.
- Every 20–25 minutes after that: a steady drip of 15–20g of carbohydrate. Small, regular doses absorb better than large boluses and dramatically reduce GI risk.
- Hydration: 400–800ml per hour depending on heat and sweat rate, with electrolytes on runs over two hours or in warm conditions.
- Within 30–60 minutes of finishing: carbohydrate plus 20–25g of protein to kick-start glycogen resynthesis and repair.
Set a recurring alert on your watch if you struggle to remember. After half a dozen long runs the rhythm becomes second nature.
Drip-feed fuel without breaking stride
Individual glucose-fructose pastilles — two chews deliver roughly 30g of carbs, with no wrappers to wrestle at mile 18.
What We Use at FTP Endurance Fuel
We built our range around the drip-feed approach described above. Our Mixed Fruit Energy Pastilles use a glucose–fructose blend for exactly the dual-pathway absorption the research supports, and because they're individual pastilles rather than a single sachet, you can take two or three every 20 minutes without breaking stride or wrestling with a wrapper at mile 18. The 1kg bulk pack also works out considerably cheaper per gram of carbohydrate than buying individual gels, which matters when you're fuelling a full marathon block of weekly long runs.
For runs where recovery is the priority — back-to-back long days or the final big sessions before a race — several of us switch to the tart cherry version for the added anthocyanins. If you're unsure where to start, the Taster Pack lets you trial them on a couple of long runs before committing to a bulk bag.
Frequently Asked Questions
What is the best fuel for long runs?
The best fuel for long runs is a glucose–fructose carbohydrate source you can take in small, regular doses — chews and pastilles are excellent for drip-feeding, gels work if your stomach tolerates repeated servings, and real food suits easier paces. Palatability matters as much as the label, because the best fuel is the one you'll actually take on schedule.
When should I start fuelling on a long run?
Take your first fuel 30–40 minutes in — it feels absurdly early, and that's the point. You're sparing glycogen, not rescuing it. After that, keep a steady drip of 15–20g of carbohydrate every 20–25 minutes, working to the clock rather than to how you feel.
How many carbs per hour do I need for a marathon long run?
For runs over 90 minutes the research-backed target is 30–60g of carbohydrate per hour, with 40–50g a practical starting point. For marathon-specific sessions of 2.5 hours or more, a trained gut can absorb up to 90g per hour — provided the fuel blends glucose and fructose, which use separate intestinal transporters.
Are energy chews better than gels for running?
Many runners find chews gentler: they're easy to portion one or two at a time rather than a whole sachet at once, they don't leave a sticky mess, and chewing stimulates saliva, which starts digestion early. Gels are fast and compact but often sit heavily after the third or fourth and usually need water alongside. Test both in training and go with what your stomach tolerates.
Fuelling well is the cheapest performance gain in running: no extra training required, just 40–50g of carbs an hour, started early and taken on schedule. Practise it on your next long run and the final miles will feel like a different sport. Ready to sort your long-run fuelling? Grab a bag of our pastilles and put the numbers above to work this weekend.
Mixed Fruit Pastilles 1kg
Glucose-fructose pastilles built for drip-feed fuelling on long runs.
£44.99
View product
Tart Cherry Taster Pack
Trial them on a couple of long runs before committing to a bulk bag.
From £5.49
View product
