Almost every long-run fuelling article tells you the same thing. Take in 30–60g of carbs per hour. Start at 30 minutes. Don’t wait until you feel low. Train your gut. The advice is correct. It is also useless on its own, because the problem most runners have isn’t that they don’t know the targets — it’s that they think they’re hitting them when they’re not.
A study published in the European Journal of Sport Science in late 2025 tracked sixty Tier 2 endurance athletes — thirty-eight marathon runners and twenty-two cyclists — through real races. The researchers measured three things: what each athlete planned to consume, what they thought they consumed, and what they actually consumed (verified through product analysis and food diaries). The findings were striking.
The carb gap, in numbers
Marathon runners: planned 25.9g/hr · actually ate 21.7g/hr · perceived they had eaten more than they did.
Cyclists: planned 58.9g/hr · actually ate 49.1g/hr · recommended target: 60–90g/hr for efforts over 2.5 hours.
Both groups fell short of guidelines. Both groups overestimated their intake. The proportional shortfall in both was roughly 17 percent.
Marathon runners were eating roughly a third of what the science recommends. And the disconnect wasn’t a knowledge gap. Most of these athletes knew the targets. They planned for them. They just didn’t execute. Some carried gels and never opened them. Some ate less than they thought they had. Some got the timing wrong. Some had GI problems and pulled back. The gap between intention and execution was the entire problem.
The takeaway is uncomfortable but useful: the issue isn’t learning what to eat. It’s tracking what you actually ate. Below is what the research recommends, the four reasons the gap exists, and a practical protocol to close it.
What the science says you actually need
Carbohydrate guidelines for endurance running aren’t controversial. They’ve been refined consistently over the past two decades and converge on the same numbers across the ACSM, ISSN, and recent meta-analyses. The principle: your liver and muscle glycogen stores are good for roughly 90–120 minutes of moderate-to-hard running. Past that, performance drops sharply unless you’re replacing carbohydrate as you burn it.
| Run duration | Carb target | Notes |
|---|---|---|
| Under 75 min | 0g | Glycogen stores cover it. Water only is fine. |
| 75–150 min | 30–60g/hr | Single carbohydrate source (glucose) is sufficient. |
| 2.5–3+ hr | 60–90g/hr | Use a glucose + fructose mix to get past 60g/hr without GI distress. |
| Ultra (4hr+) | 60–120g/hr | Highly individual. Real food becomes more practical. |
Two numbers in there matter more than the rest. The first is 60 grams per hour — the maximum your gut can absorb from glucose alone, regardless of how much you swallow. To go higher you need a second carbohydrate type (typically fructose) that uses a different intestinal transporter. This is why high-end sports gels use a 1:0.8 ratio of maltodextrin to fructose: the body can absorb both pathways simultaneously, getting you to 90g/hr and beyond.
The second is 30 minutes. That’s when fuelling should start. Not when you feel low — by then you’re already chasing a deficit. Start early, take small amounts often, and let absorption stay ahead of oxidation.
The body burns carbohydrate at a rate the gut can’t match unprompted. Fuelling isn’t replacing what you used — it’s feeding a system that’s about to run out faster than you can keep up with.
Why most runners fall short (and don’t know it)
Four things drive the planned-versus-actual gap. Most runners have at least two of them.
1. The “I’ll grab one when I need it” mistake
Fuelling reactively — waiting until you feel a dip — means you’re already 20–30 minutes behind. Carbohydrate ingested now isn’t in your bloodstream for another 10–15 minutes. By the time the energy lands, you’ve lost pace, your stomach is more stressed than it would have been earlier, and you’re trying to catch up from a deficit. Pre-cue your fuelling on the clock, not on feel.
2. Overestimating what you finished
The Lanpir study found marathoners’ perceived intake was higher than their actual intake by a statistically significant margin. This is the most subtle failure mode: you came home with one fewer gel than you started with, and assumed the missing one went down. It didn’t — you bit a corner off, took half, decided it tasted off, and tucked the rest into your shorts. Or you opened two and only finished one. Without measurement you have no idea.
3. Going too high too fast
An untrained gut tops out around 30g/hr. Try to do 75g/hr cold and the symptoms appear — nausea, bloating, cramps, a sudden need for a toilet. The natural response is to stop fuelling entirely for the rest of the run, which guarantees a bonk. The protocol below builds tolerance gradually so you don’t hit this wall.
4. Carbs without fluid
Carbohydrate concentration in the stomach matters. Take a 25g gel with no water and it sits there at high osmotic load, pulling fluid into the gut and slowing emptying. Pair every gel with 100–200ml of water and the same gel absorbs cleanly. Heavy sweaters and warm-weather runners need even more — 400–800ml per hour of fluid alongside the fuel.
The 4-step protocol
This is the framework. Test it in training, never on race day.
Calculate your hourly target by duration and intensity.
For runs of 75–150 minutes, target 30–60g of carbohydrate per hour. For runs longer than 2.5 hours, target 60–90g. The longer and harder the effort, the closer to the upper end. Don’t fuel a 60-minute easy run — you don’t need it.
Start fuelling at 30–40 minutes.
Set a watch reminder. Take your first feed before you feel any drop. Then every 20–30 minutes after that. Smaller, more frequent feeds beat one large dose in absorption efficiency and GI comfort.
Measure what you actually took in.
Count gels in, count gels out. Note what came back unused. Match it against time elapsed and divide. The first time most runners do this they’re shocked at how short they fell. Awareness alone fixes 60 percent of the gap.
Build your gut over 4–8 weeks.
Add 10g per hour to your long-run intake every 1–2 weeks. If a step causes GI distress, hold there for an extra week before progressing. Most runners get from 30g/hr to 60g/hr in 4 weeks, and to 90g/hr in 8–12 weeks. The gut adapts faster than most people expect.
What to actually carry
The format doesn’t matter as much as the grams. Gels, chews, sports drink, real food — what matters is how much carbohydrate you get in per hour and how well you tolerate it. Below are the formats that work, ranked by practicality and grams per serving.
| Format | Carbs per serving | Best for |
|---|---|---|
| Energy gel (standard) | 20–30g | Convenient, fast-absorbing. The default. |
| High-carb gel (90g) | 60–90g | Long efforts. One gel replaces three. Glucose-fructose blend. |
| Sports drink (isotonic) | 30–60g per 500ml | Hydration + fuel in one. Easier on the stomach. |
| Chews / blocks | 20–30g per packet | Solid texture. Slower to eat — spread the dose. |
| Banana | 27g | Real food. Research shows it performs equivalently to gels. |
| Dates | 18g per 2 dates | Compact, cheap, easy on the stomach. |
| Salted potato | 30g per small potato | Ultra runners’ staple. Real carbs + sodium. |
| Jam sandwich (white bread) | 40–50g | Cheapest viable fuel. Easy to digest. |
For more on the staples that should anchor your daily training nutrition — not just race day — see our breakdown of the best value carbs for runners and the daily carb intake numbers most runners undershoot.
One last thing about race day
Nothing new on race day. Every gel, every drink, every solid food choice should have been used in training first. The Lanpir study’s biggest finding wasn’t that runners ate too little — it was that the gap between plan and execution was wide enough to cost them performance. The fix isn’t a better plan. It’s a measured plan. The longer your race, the more this matters.
You can’t fix a fuelling problem you can’t see. The most useful thing you can do for your next long run isn’t to plan harder — it’s to count what actually went down.
Kovr logs in-session fuel in one tap and shows the gap between what you planned and what you actually took on.
After every session over 60 minutes, Kovr asks one question: how much did you fuel? Four options — none, ~30g, ~60g, or ~90g per hour. The activity card sees the fuel. The pattern engine uses it. Over time, your long runs stop being a guess.
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Frequently asked questions
How many carbs should I eat during a long run?
For runs of 75 minutes to 2.5 hours, aim for 30–60g of carbohydrate per hour. For runs longer than 2.5 hours, aim for 60–90g per hour. Faster, harder efforts sit at the upper end of each range. Most recreational runners fall well short of these targets without realising it.
When should I start fuelling on a long run?
Start at 30–40 minutes, before glycogen depletion sets in. Don’t wait until you feel low — by the time you feel a dip in energy, you are already behind. Take small amounts every 20–30 minutes thereafter.
Do I need gels for a long run, or can I use real food?
Both work. Gels and chews are easier to carry and absorb fast. Real food — bananas, dates, salted potatoes, jam sandwiches — is cheaper and easier on the stomach for many runners. Bananas have been shown in research to perform equivalently to commercial sports products. The constraint is total grams of carbohydrate per hour, not the form it comes in.
What is gut training and how long does it take?
Gut training is progressively increasing carbohydrate intake during long runs so your stomach learns to absorb more without distress. Most athletes move from tolerating 30g per hour to 60g per hour in 4 weeks, and up to 90g per hour in 8–12 weeks. Add 10g per week during one or two long sessions.
Why do I feel sick when I try to fuel during a long run?
GI distress during fuelling usually comes from one of three sources: too much carbohydrate from a single source (the body can only absorb about 60g/hr of glucose alone — use a glucose + fructose mix to get higher), too little water with the fuel, or an untrained gut. The fix is to slow down the build, pair every gel with fluid, and stay consistent with weekly gut-training sessions.
How much water should I drink during a long run?
Around 400–800ml per hour depending on temperature, sweat rate, and intensity. Heavy sweaters and hot conditions push toward the upper end. Pair every gel or fuel intake with at least a few sips of water to support absorption — carbohydrate without fluid sits in the stomach.
Should I take electrolytes on a long run?
For runs over 90 minutes, especially in warm conditions or for heavy sweaters, yes. Aim for 300–1000mg of sodium per hour. Plain water alone for long durations in heat can cause hyponatraemia and worsen GI symptoms. Most sports drinks and some gels include electrolytes; if you fuel with whole food, add electrolyte tablets to your water.
Sources cited
- Lanpir et al. (2025). Under Consumed and Overestimated: Discrepancies in Race-Day Carbohydrate Intake Among Endurance Athletes. European Journal of Sport Science. View study
- Jeukendrup, A. (2017). Training the Gut for Athletes. Sports Medicine. View article
- Thomas, Erdman & Burke (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance.
- Burke et al. (2011). Carbohydrates for training and competition. Journal of Sports Sciences.