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You’ve done the 16-miler. Legs felt fine until mile 11, then everything went heavy and your stomach started doing something unhelpful. Or maybe it was simpler: you just ran out of steam, slowed to a shuffle, and spent the last three miles wondering why you bothered training at all. Nine times out of ten, that’s not a fitness problem. It’s a fuelling problem.
Long run nutrition and hydration isn’t complicated science reserved for elite marathoners with sports dietitians on speed dial. It’s a handful of numbers you can memorise, applied consistently, adjusted for your own gut. This guide covers what to eat before a long run, what to take during it, how much to drink, and how to stop guessing.
The honest bit first: your first few attempts at fuelling will probably go slightly wrong. Too much, too little, wrong timing, stomach revolt at mile 8. That’s normal and it’s exactly why you practise this on training runs and never — ever — try something new on race day.
Why long runs need a different approach than shorter ones
Anything under about 75–90 minutes, your body can mostly run on what’s already stored in your muscles and liver (glycogen) plus whatever you had for breakfast. Past that point, glycogen stores start running low, and if you don’t top up with carbohydrate, your pace will fall off a cliff — not gradually, but suddenly. That’s “hitting the wall,” and it’s avoidable with a plan, not willpower. If you want the full mechanics of why this happens and how to head it off, we’ve covered it in detail in our piece on hitting the wall in a marathon.
Hydration follows a similar logic but on a slower timeline — you can run dehydrated for a while before it bites, but once it does, it compounds everything else: higher heart rate for the same pace, worse heat tolerance, slower gut absorption of the carbs you’re trying to get in. The two problems feed each other.
Before the run: what to eat and when
The goal of your pre-run meal is simple — top up liver glycogen and avoid starting a 2-hour run on an empty stomach, without weighing yourself down with fat or fibre that sits badly.
3–4 hours before: A proper meal — 60–100g of carbohydrate, moderate protein, low fat and low fibre. Porridge with banana, toast with honey and peanut butter, a bagel with jam, rice with a bit of chicken. This is where your usual breakfast works fine for most people.
1–2 hours before: A smaller top-up if you’re running early and that 3-hour window isn’t realistic — a banana, a slice of toast, a small bowl of cereal, 150–250ml of a carb drink. Keep fat and fibre low here; this isn’t the time for a big bowl of bran flakes or a fry-up.
30 minutes before (optional): A gel or a few dates if you’re running first thing and haven’t eaten much. Not essential, but useful if you tend to fade in the first 20 minutes.
What to avoid: high-fat food (bacon, cheese, pastries), high-fibre food (big salads, beans, wholegrain everything) and alcohol the night before in anything beyond moderate amounts — all three increase the odds of a mid-run gut emergency.
During the run: the carbohydrate numbers that actually matter
This is where most runners either do nothing (and pay for it after mile 10) or wing it with whatever gel was in the drawer. Here’s the actual guidance, based on what sports nutrition research consistently shows about carbohydrate absorption during exercise:
| Run duration | Carbs needed | Practical options |
|---|---|---|
| Under 60 min | None required | Water if hot |
| 60–90 min | Optional, 15–30g/hour | Half a gel, a few jelly babies |
| 90 min–2.5 hrs | 30–60g/hour | 1 gel every 30–45 min, or sports drink + chews |
| Over 2.5 hrs | 60–90g/hour | Mix of glucose + fructose sources (gels + drink), trained gut required |
The “mix of glucose and fructose” point matters more than people realise — your gut can only absorb so much of one sugar type per hour, roughly 60g of glucose alone, but combining glucose and fructose sources (most race gels are already formulated this way) lets you push past that ceiling toward 90g/hour if you’ve trained your gut to handle it. You don’t start there. You build up over weeks, same as you build up your mileage.
If gels aren’t your thing — some runners find the texture or sweetness impossible past mile 15 — real food works too: dates, pretzels, even flat cola in small sips. The carbohydrate source matters less than hitting the hourly target consistently. For a full breakdown of specific products and what they actually taste and feel like mid-run, our review of the best energy gels for running in the UK is worth a look before you commit to one brand for race day.
Hydration: how much, and how to tell if you’re drinking enough
Forget the old “8 glasses a day” rule and the equally unhelpful “drink as much as possible.” Both are wrong for runners. The useful approach is this:
- Before the run: 400–600ml in the 2 hours beforehand, not chugged in one go.
- During the run: roughly 400–800ml per hour, more in heat, less in cool weather. That’s a rough guide, not gospel — sweat rates vary hugely between individuals.
- Test your own sweat rate: weigh yourself before and after an hour’s run without drinking. Each kg lost is roughly 1 litre of sweat. If you lost 0.8kg, you need about 800ml/hour on similar runs.
For runs over 60–75 minutes, especially in warm weather, you also need electrolytes — specifically sodium — not just water. Plain water during a long sweaty session can actually dilute your blood sodium further and, in extreme and rare cases, cause hyponatraemia. For most of us the risk is milder but real: cramping, nausea, that foggy, flat feeling in the last few miles. A sports drink or electrolyte tablet with 300–700mg sodium per litre covers most runners’ needs. The NHS guidance on exercise and hydration is a sensible starting point if you want the basics without the marketing noise.
If you’re deciding between products, we’ve done an honest side-by-side in our electrolyte drinks comparison — worth reading before you stock up on whatever’s on offer at the supermarket.
Signs you’re getting it wrong (and what they mean)
| Symptom | Likely cause | Fix |
|---|---|---|
| Sudden, dramatic fatigue around mile 10–16 | Glycogen depletion | Start fuelling earlier, by 45 min in |
| Nausea, bloating, cramping gut | Too much sugar too fast, or new product on race day | Spread intake, practise in training |
| Headache, dizziness, dark urine | Dehydration | Increase hourly fluid, check sweat rate |
| Muscle cramping late in the run | Often sodium, sometimes just fatigue | Add electrolytes, don’t rely on water alone |
| Feeling fine but suddenly flat near the end | Under-fuelling across the whole run | Recalculate hourly carb target honestly |
Our deeper dive on dehydration while running covers the early warning signs in more detail if you want to get ahead of it rather than reacting mid-run.
Recovery: the window after the run matters too
The 30–60 minutes after a long run is when your muscles are most receptive to replenishing glycogen and starting repair. You don’t need a precise ratio obsession, but a rough target of 1g carbohydrate per kg bodyweight plus 20–25g protein within that window works well for most people — a recovery shake, chocolate milk, or just a normal meal eaten promptly rather than two hours later. If you’re training several long runs a week during marathon block, consistent protein timing across the week matters more than any single post-run snack — our guide on best protein foods for runners’ muscle recovery goes into specifics on food choices and timing.
Practising this before race day
Every number above is a starting point, not a prescription. Your gut, your sweat rate, your tolerance for sweetness at mile 18 — all individual. The only way to find your own numbers is to rehearse them on training long runs, ideally the ones that mimic race pace and duration. If you’re building toward a marathon, this is exactly what carb loading and race week nutrition should extend, not replace — see our guide on carbohydrate loading before a marathon for how the final days tie into what you practise on long runs.
The Honest Takeaway
- Anything over 90 minutes needs 30–60g of carbs per hour, taken early and often — not just when you start feeling bad.
- Hydrate 400–800ml per hour depending on heat and your own sweat rate, and include sodium, not just water, on anything over an hour.
- Test every gel, drink and fuelling strategy on a training run first. Race day is not the place for experiments, however appealing the free gel sample on the course might look.
- Eat a proper carb-focused meal 3–4 hours before, keep it low fat and low fibre, and don’t skip breakfast because you’re nervous.
- Recover with carbs and protein within an hour of finishing — it genuinely makes the next day’s legs feel less wrecked.