Fueling a marathon well comes down to one core problem: your body can store roughly 1,250 to 2,270 calories of glycogen in your leg muscles, but running 26.2 miles at race pace burns more than that. Without a smart fueling plan, you’ll likely hit the wall around mile 21, where more than two-fifths of marathon runners experience severe energy depletion. The good news is that with the right strategy in the days, hours, and miles leading up to and through the race, you can keep your engine running strong to the finish.
Carb Loading in the Days Before
Carb loading isn’t about one giant pasta dinner the night before. It’s a deliberate 36- to 48-hour process of eating 10 to 12 grams of carbohydrates per kilogram of body weight each day while tapering your training. For a 70-kilogram (154-pound) runner, that means 700 to 840 grams of carbs per day, which is a serious amount of food. Rice, bread, pasta, potatoes, oatmeal, fruit, and sports drinks all count toward that total.
The goal is to pack your muscles with as much glycogen as possible. A trained athlete’s muscles normally store glycogen at a moderate density, but a proper loading protocol can nearly double that capacity. This is your largest fuel tank, and filling it completely before the race is the single most impactful thing you can do.
Spread your carbs across meals and snacks throughout those two days rather than trying to eat everything at once. Keep fat and fiber moderate so you don’t end up with stomach issues on race morning. Many runners find that switching to lower-fiber, easily digestible carb sources (white rice instead of brown, white bread instead of whole grain) helps them eat enough without feeling bloated.
What to Eat on Race Morning
Your pre-race meal tops off liver glycogen, which drops overnight while you sleep. The liver holds roughly 350 calories in its normal state, and you want that reservoir full. Aim for 1 to 4 grams of carbohydrates per kilogram of body weight before the start, with the amount depending on how far out you eat. Four hours before the gun, you can handle a larger mixed meal with some fat and protein. Two to three hours out, which is what most runners prefer, scale back to a moderate carb-focused meal with less fat.
In the final hour before the start, stick to small amounts of low-fiber, simple carbohydrates: a sports drink, a few bites of a white bagel, or a gel. The closer you get to race time, the simpler your food should be so it clears your stomach quickly. Whatever you choose, practice it in training. Race morning is not the time to experiment.
Fueling During the Race
This is where most runners either get it right or fall apart. The traditional recommendation for events lasting longer than two and a half hours is 60 grams of carbohydrates per hour, but current sports nutrition guidelines push that number to 90 grams per hour for marathons. Recent research on mountain marathon runners found that those consuming 120 grams per hour showed significantly less muscle damage than those at 60 or 90 grams, suggesting that higher intake may offer additional protective benefits for demanding events.
The catch is that your gut can only absorb about 60 grams per hour of glucose through a single transport pathway. To get above that ceiling, you need products that combine glucose (or maltodextrin) with fructose, because fructose uses a separate absorption pathway in the intestine. Look for gels, chews, or drink mixes that use both carbohydrate sources. A ratio of roughly 1 to 1 (maltodextrin to fructose) is considered optimal. This combination speeds gastric emptying and reduces the nausea and cramping that come from overloading a single pathway.
Start fueling early, within the first 30 to 45 minutes, and stay consistent. Waiting until you feel depleted means you’re already behind. Most runners space their intake every 15 to 20 minutes rather than taking large amounts at once. A typical approach is one gel every 20 minutes alongside sips of water, but the exact format (gels, chews, sports drink, or a mix) is personal preference. The total hourly carbohydrate count matters more than the delivery method.
Training Your Gut
If you’ve never eaten 90 grams of carbs per hour while running, your stomach will likely protest on race day. The solution is to practice your fueling plan during long training runs, starting weeks or months before the marathon. A high-carbohydrate diet and regular practice with race-day nutrition increase the density and activity of carbohydrate transporters in your intestinal lining, allowing you to absorb and use more fuel without GI distress. This adaptation is real and measurable, but it takes consistent practice. Build up gradually, starting with smaller amounts and increasing over the course of your training cycle.
Hydration and Sodium
Fluid needs vary enormously from runner to runner. A larger person running fast in hot weather might sweat over 2 liters per hour, while a smaller runner in cool conditions might lose half a liter. The best way to estimate your sweat rate is to weigh yourself before and after a training run (without drinking during it). Every kilogram lost equals roughly one liter of sweat per hour of running.
If you don’t know your sweat rate, a practical starting point is 3 to 4 long sips of water every 15 minutes, adjusting based on thirst and conditions. Overdrinking is a real risk too. Drinking far more than you sweat out can dilute your blood sodium to dangerous levels, a condition called hyponatremia. Drink to thirst and use your sweat rate data to set a reasonable ceiling.
Sodium replacement matters during a marathon because you lose significant amounts in sweat, typically between 300 and 600 milligrams per hour depending on your individual sweat composition and rate. The American College of Sports Medicine recommends replacing 300 to 600 milligrams of sodium per hour during prolonged exercise. Many sports drinks and gels contain some sodium, but heavier sweaters may need additional salt tabs. If you notice white residue on your clothes or skin after long runs, you’re likely a salty sweater who benefits from extra sodium.
Recovery Nutrition After the Finish
Your muscles are most receptive to restocking glycogen in the first two hours after you finish, with the first 30 minutes being the prime window. Aim for about 1 gram of carbohydrate per kilogram of body weight paired with 0.5 grams of protein per kilogram within that first half hour. For a 70-kilogram runner, that’s roughly 70 grams of carbs and 35 grams of protein: think a recovery shake, chocolate milk with a banana, or a sandwich with juice.
After that initial refueling, continue eating carbohydrate-rich meals throughout the day. If rapid recovery matters (for example, if you have another event soon), target more than 8 grams of carbohydrates per kilogram of body weight across the full day, with at least 1.2 grams per kilogram per hour for the first four hours. For most single-marathon runners, simply eating well and prioritizing carbs and protein in the hours after finishing is enough to support recovery without precise gram counting.
Putting It All Together
A complete marathon fueling timeline looks like this:
- 36 to 48 hours before: 10 to 12 grams of carbs per kilogram per day, low fiber, reduced training
- 2 to 3 hours before: 1 to 3 grams of carbs per kilogram, moderate meal with limited fat
- Final hour before: small amount of simple carbs, sips of sports drink
- During the race: 60 to 90+ grams of carbs per hour from mixed glucose-fructose sources, starting within the first 30 minutes
- Fluids during: drink to thirst, guided by your sweat rate, with 300 to 600 milligrams of sodium per hour
- Within 30 minutes after: 1 gram carbs plus 0.5 grams protein per kilogram of body weight
The single most important principle across all of this: practice everything in training. Your long runs are dress rehearsals for race-day nutrition. Test your gels, your drink mix, your pre-run breakfast, and your timing. The runners who nail their fueling on race day are the ones who’ve already done it dozens of times before the starting line.