Fueling for a marathon: Why is it so important?

Mastering your marathon nutrition strategy is just as important as your training plan. In this comprehensive guide, we’ll break down exactly what to eat and drink before, during, and after your race to keep your energy high, your stomach settled.

If you’re gearing up to take on the legendary 26.2 miles—whether at the London Marathon or a local race—you’ve probably started thinking about fuelling for a marathon. And if you haven’t yet? Don’t stress—there’s still time to dial in your marathon nutrition plan. The truth is, running a marathon isn’t just about pounding the pavement; it’s about knowing what to eat before a marathon, how to hydrate smartly, and how to fuel for a marathon from start to finish.

Ideally, your long runs should have been a testing ground—experimenting with energy gels, chews, sports drinks, or even whole foods—to discover what sits well with your gut and keeps you going strong. Maybe you’ve figured out your go-to race day breakfast, or tried out carb loading strategies in the week leading up to race day. But if you haven’t explored your race day nutrition, don’t panic.

Now is the perfect time to ask the big questions: How many carbs do I need during a marathon? What gels are best for marathon runners? Should I drink water or sports drinks while running? This is your moment to nail down your hydration strategy, calculate your carb intake per hour, and determine the balance of electrolytes and fluids that will keep your body in rhythm from mile one to mile twenty-six.

Fuelling might feel like another layer of complexity—but trust us, it’s what helps you avoid “the wall” and finish strong. This marathon nutrition guide will walk you through every key detail, from pre-race meals and mid-race fuelling to post-marathon recovery food. Whether you’re wondering what to eat the night before a marathon or when to start fuelling during a marathon, we’ve got you covered—so you can run smart, fuel right, and race your best.

1. Why Is Fuelling for a Marathon So Important?

Let’s get real—fuelling for a marathon isn’t just a nice-to-have; it’s essential. Whether you're chasing a PB or just hoping to finish strong, what you eat and drink before and during the race can make or break your experience. One misstep in your marathon nutrition strategy, and the infamous “wall” is waiting for you at mile 20.

When your body runs out of glycogen—the stored form of carbohydrate—it hits emergency mode. This is what runners mean when they talk about “hitting the wall”: complete exhaustion, heavy legs, and a brain that just wants to quit. On top of that, if you're not keeping up with hydration and electrolyte intake, you may also suffer from dehydration symptoms like nausea, dizziness, or stomach upset, all of which can derail your race and even put your health at risk.

But here’s the good news: if you craft a smart, personalized plan for what to eat before a marathon, how to hydrate, and how to refuel mid-run, you’ll feel strong and steady all 26.2 miles. Whether it’s sports drinks, energy gels, or carb-rich meals in the days leading up to the race, a well-thought-out approach ensures your energy tank stays topped up and your body stays balanced.

2. How Many Gels Should You Take During a Marathon?

This is one of the most common questions in any marathon nutrition guide: “How many gels should I take during a marathon?” And the answer depends on your pace, your gut, and the carbohydrate content of your chosen product.

Carbohydrates are your body’s premium-grade fuel when running. They’re converted to glucose, stored as glycogen in your muscles and liver, and burned for energy with every stride. The problem? You only have so much in the tank. For most runners, glycogen stores last for about 60 to 90 minutes of running—less if you’re going hard.

So how do you avoid the crash? Experts recommend taking in 30–60 grams of carbs per hour for the first half of your race, and up to 90 grams per hour in the later stages if your stomach can handle it. That’s where energy gels, sports drinks, or chews come in. They're compact, easy to digest, and perfect for on-the-go fuelling.

Let’s say your go-to gel has 23g of carbs. Over a four-hour marathon, you’d need around six gels to hit the lower end of the carb goal—roughly 34.5g/hour. If you're wondering “When should I start fuelling during a marathon?”, the answer is early: within the first 30 minutes of running, then continue every 30 to 40 minutes. Set reminders on your watch, write notes on your hand—whatever helps you stay consistent.

And here’s a crucial race day tip: never try new nutrition products on race day. Experiment during long runs. Train your gut. See what fuelling strategy feels right for you—whether that’s marathon energy gels, chews, sports drinks, or even bananas or jelly beans.

The best running gels for marathons are the ones your body trusts and absorbs well. And remember, every athlete is different, so your fuelling rhythm is yours to discover. Practice makes confident—and confident runners crush marathons.

3. How Much Water Should You Drink During a Marathon?

Proper hydration is a core pillar of fuelling for a marathon—it’s not just about carbs and gels. Your water intake can mean the difference between powering through 26.2 miles or struggling to stay upright by mile 18.

Water does more than quench your thirst. It supports thermoregulation (cooling your body), keeps your blood volume stable, and prevents your heart rate from skyrocketing due to dehydration. When your body’s fluid levels drop, your core temperature rises, your blood thickens, and your effort level feels 10x harder. That’s when fatigue, dizziness, dry mouth, muscle cramps, and even headaches kick in—signs your body is dehydrated and waving the white flag.

So, how much water should you drink during a marathon? There’s no one-size-fits-all. Your needs depend on factors like sweat rate, running pace, body weight, weather conditions, and even gender. Most runners lose between 400ml to 2,400ml of sweat per hour, and the general hydration recommendation ranges from 300ml to 800ml per hour. Use your training runs to observe how much you sweat and how your body responds to different volumes of fluid.

And don’t wait until race time to hydrate. Start hydrating the day before the race, and on race morning, sip around 530ml of water with electrolytes starting three hours before your start time. If your urine isn't light-colored, drink an additional 400ml of water to reach optimal hydration.

This isn't just about comfort—it's about performance, endurance, and finishing strong. Combine your marathon hydration strategy with a solid carb plan, and you’re setting yourself up for success.

4. Do You Really Need Electrolytes for a Marathon?

Short answer? Yes. Fuelling for a marathon goes beyond water and carbs—electrolytes are your secret weapon for long-haul stamina.

When you sweat, you’re not just losing fluids; you're also losing sodium, potassium, magnesium, and chloride—critical electrolytes that regulate muscle function, nerve impulses, and fluid balance. Without replacing them, you risk cramping, fatigue, nausea, and overall poor performance.

So, do you need electrolytes for a marathon? Absolutely—especially in races longer than 90 minutes or in hot conditions. Sodium loss can vary wildly from runner to runner—from 115mg to 2,000mg per 1,000ml of sweat. That’s why some runners feel wrecked after an hour, while others can cruise for two hours without issues. Understanding your sodium loss is key to creating a smart race day nutrition plan.

Most electrolyte drinks or tablets provide 250–300mg of sodium per serving. If you're diluting electrolytes into 750ml of water, you’d need to drink over 2L per hour to meet your full sodium requirement—impractical in most race settings. That’s where salt capsules, electrolyte sticks, and concentrated drinks come in handy. They deliver more sodium in smaller doses—perfect for staying on top of your hydration without chugging liters of water.

Sports nutrition experts typically recommend aiming for 700–900mg of sodium per hour during long runs or marathons. You can start sipping electrolytes the day before your race to get ahead of any imbalances, then maintain intake during the race through your preferred method—tablets, capsules, or electrolyte-infused sports drinks.

Bottom line: electrolytes are essential for avoiding dehydration, maintaining endurance, and keeping cramps at bay. Don’t ignore this part of your marathon training nutrition plan—your legs will thank you at mile 22.

5. How Can You Avoid Stomach Issues During a Marathon?

Ah yes—the dreaded mid-run gut twist. Runners often report nausea, cramps, or bathroom emergencies when trying to take in running gels or energy chews during a marathon. But here’s the truth bomb: it’s not always the gels that are to blame.

According to sports dietitian experts, the main culprit is usually a sodium imbalance combined with dehydration. When you're fuelling for a marathon, your body diverts blood away from the digestive system to focus on your working muscles. If you’re consuming concentrated carbs—like glucose-packed gels—without enough fluid and sodium, your gut gets overwhelmed. The sugar sits there, undigested, causing that infamous stomach upset.

So, how do you avoid GI distress? Balance is everything. Match your gel intake with hydration and electrolytes, especially during warmer races. Test different sports nutrition products during your long training runs to find your sweet spot. And remember—what works for your running buddy might not work for you.

6. What Should You Eat Before a Marathon?

One of the most important parts of fuelling for a marathon happens before you ever toe the start line. Your pre-race meals set the stage for how well you’ll perform and how strong you’ll feel across all 26.2 miles.

Let’s start with the carb loading game plan. In the final 2–3 days leading up to your marathon, gradually increase your carbohydrate intake to max out your glycogen stores—your body’s primary energy reserve. This doesn’t mean stuffing yourself silly. Instead, make smart swaps: trade a snack of fruit or yogurt for a bagel or a slice of toast, or swap out veggie-heavy meals for pasta, rice, or potatoes. This approach supports marathon training nutrition plans without making you feel bloated or sluggish.

For dinner the night before your race, go with high-carb, low-fiber, and low-fat meals. Think: pasta with marinara, garlic bread, or rice with grilled chicken or tofu. Avoid excessive fats, spices, or roughage that could disrupt your stomach. And here’s a pro tip: make lunch your bigger meal, and opt for something lighter in the evening like sweet potato and soup with a slice of bread.

On race morning, nerves might mess with your appetite. Don’t stress—it’s what you ate in the days before that really matters. Still, it’s best to eat 2–3 hours before the race, choosing easy-to-digest carbs. A white bagel with banana and a smear of peanut butter, or porridge topped with honey and a few nuts, hits the sweet spot.

Stick to low-fiber carbs like white bread instead of brown, and avoid trying anything new. Test your race day nutrition tips during your long runs, so by marathon day, your breakfast feels like second nature. Your stomach will stay settled, your energy will be topped off, and your body will be primed for the miles ahead.

SUMMARY

Fuelling for a marathon is more than just gulping down a gel mid-run—it’s a full-cycle strategy that starts days before race day and continues long after you cross the finish line. This in-depth blog explores every angle of marathon nutrition, from carb loading techniques and pre-race meals to hydration strategies, electrolyte balance, and how to choose the best energy gels and chews. You'll also learn how much water you need per hour, how to avoid stomach issues, when to take your first gel, and what to eat after your race for optimal recovery. With expert-backed advice and answers to the most common runner questions, this guide is your ultimate marathon nutrition handbook.