Marathon Fueling Guide: Carb Intake and Hydration for Race Day

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All the miles you log during marathon training are only part of the road to running a successful race. How you fuel those miles during the event is just as important as your training.

In fact, according to a 2025 Sports Medicine-Open study of 160 Seville Marathon runners (mostly men), those who met the carbohydrate intake recommendations during the race—in this case, meaning they took in 60 to 90 grams of carbs per hour—were more likely to finish the marathon in under three hours, compared to those who didn’t meet those carb recommendations.

The amount of carbs—along with fluids and electrolytes—isn’t the only variable when it comes to fueling your race successfully. Timing also matters. Your body can only utilize a specific amount of the fuel and hydration throughout the race, and you need to constantly restock your sources to avoid depleting them.

That’s why we asked two registered dietitians who work with runners to break down the macros, hydration, and sodium you need throughout marathon race day. With this guide, you can practice your fueling in training and figure out what will keep you energized enough to avoid bonking and run strong across the finish line.

What to Eat Before You Start

🥯 Fuel Breakdown

• Calories: 400 to 800
• Carbs: 80 to 150 grams
• Fats: up to 15 to 20 grams
• Protein: up to 15 to 20 grams
• Hydration: 16 to 24 ounces
• Sodium: 500 to 700 milligrams

While you’ll carb load in the days leading up to your 26.2-miler, to stock your glycogen stores, eating a carb-packed breakfast before you hit the start is also key for topping off your liver glycogen.

Runners should consume 1 to 4 grams of carbohydrates per kilogram of bodyweight (or about 0.45 to 1.8 per pound) about two to four hours before the start.

Eat at the higher end of the calorie range, if you can do it comfortably. “That’s really going to set you up to have great energy later on in the marathon, because the wheels usually fall off in the final 10K,” says Alex Larson, RD, a Minnesota-based registered dietitian who works with endurance athletes. “If you can carb-load really well in advance [and fill up throughout the race], you typically still have some good energy stores and go strong in the final 10K.”

In general, keep protein and fat to a minimum, less than 20 grams of each, but make sure to have some of those macronutrients in your breakfast. “If you have straight carbs at breakfast, your blood sugar will increase pretty quickly, and it can make you feel a bit sick,” Larson says. “Having some protein and fat with a high-carb meal or snack helps stabilize that blood sugar.”

Oatmeal or cream of rice are convenient, carb-centric breakfast options that can be easy to make in a hotel room. A granola bar, banana, and sports drink can also work. Or, go for Larson’s favorite prerace breakfast: pancakes with syrup.

If you have a later start time, such as 10 or 11 a.m., and get up early Larson suggests eating two breakfasts: one after you wake up and the other an hour before your race. Similarly, double your fluid intake and sodium.

Some runners may also find it helpful to have a gel or energy chews about 15 minutes before the race, “just to get some fresh energy in your bloodstream right as you start,” Larson says.

What to Eat Throughout 26.2

💦 Fuel Breakdown per Hour

• Calories: 120 to 480
• Carbs: 30 to 120 grams
• Fats: As little as possible
• Protein: As little as possible
• Hydration: 8 ounces
• Sodium: 200-500 milligrams

These nutrient ranges are wide because runners come in all shapes and sizes, and they run at a variety of paces, too, and that can affect how fast you go through your glycogen stores. How much you sweat also determines how much fuel you need, particularly in terms of electrolytes.

Holley Samuel, RD, CSSD, a board-certified specialist in sports dietetics and runner, suggests aiming for the middle to upper end of the carb range (60 to 90 grams per hour) if you can tolerate that much food. Just understand “there’s a line of diminishing returns for every person where they start to feel like it’s too much,” she says, which is why you have to practice in training to find your tolerance.

Because the need for carbohydrates is mostly driven by the intensity of the effort, the very high end of carbohydrate intake (90 to 120 grams per hour) is best suited for the elite runners whose running paces demand the high rate of energy intake for fueling those very intense efforts.

However many calories you plan to take in during the race, the experts suggest fueling at least every 30 minutes with 15- to 60-gram doses of carbs so you meet the hourly goals of 30 to 120 grams. If you run about a 10-minute mile, you can plan to take in fuel every three miles or for those going faster, every four to five miles. (Mile markers serve as a solid checkpoint for fuel intake!) A simple way to break it down is to split the suggested carbs and calories in half each time you fill up.

Keep in mind, some runners perform better when they take in carbs every 15 to 20 minutes.

For an example of how to break it down: Runner’s World recommends Chargel Gel Drink for marathons, which has 45 grams of carbs. Following the 30-minute or three-mile rule, you’d get in 90 grams of carbs per hour. (This is on the higher end, so something you definitely want to practice in training. You can always start with half of the Chargel every 30 minutes during long runs, see how it settles, and work up to the full product.)

The same rule applies for gummies, like Clif Blocks, which contain 24 grams of carbs in a three-piece serving. To meet that higher carb intake of 90 grams per hour, you’d need to take about six gummies (one whole packet), every 30 minutes. Or, if you’re aiming for 60 grams per hour, go for three to four gummies every 30 minutes.

Splitting up carb intake will help improve GI toleration and absorption especially at higher intensities, Samuel explains. Also, being consistent with your gels and other energy sources, as opposed to waiting until you’re depleted of energy, will support a better race performance.

If you prefer sports drinks, such as Gatorade Endurance—which Samuel recommends because it has more sodium than regular Gatorade (300 milligrams per 12 ounces), along with carbs (21 grams per 12 ounces), and it’s a product you’ll find on many race courses—consider dividing a serving into small flasks or drinking half a 12-ounce bottle every 30 minutes. Just make sure you sip it rather than gulping it down, which can lead to GI upset.

It’s important to incorporate sodium with your fluids every hour. “We don’t just want to chug a bunch of water, because that can be dangerous and set us up for hyponatremia, which is a low blood sodium condition that can cause seizures and poor muscle contraction,” Samuel says.

To get in sodium, you can focus on that carb-and-electrolyte drink, like Gatorade Endurance, or sip plain water with a gel or a serving of sport gummies with added sodium to ensure you get about 200 to 500 milligrams of sodium per hour, depending on your sweat rate and hourly fluid intake. While salt tablets are an option, they’re not necessary if you’re drinking a sports beverage or if you’re taking in sodium via your gels and gummies.

Combining carbohydrate and electrolyte sources like gummies, gels, and sports drinks is a convenient way to meet your hourly needs for carbs, fluids, and sodium, while getting a variety of foods and drinks.

Keep in mind, you may need more than eight ounces of water if you’re racing in hot, humid weather or if you tend to sweat a lot. “It’s about finding what works for each individual,” Samuel says.

A key component of prerace training is dialing in your fluid, sodium, and carbohydrate intake per hour for your marathon-pace long runs, as well as your tempo runs. Higher temperatures and faster paces (think: fast starts, finishing kicks, and hill surges) make digestion more challenging so it’s important to practice race-day fueling using the same products and amounts in as many types of sessions as possible that mimic the race-day effort and conditions.

To make sure you have enough fuel for race day, count out how many gels, gummies, or bottles you’ll need to make it from start to finish in your projected race time, considering those 30-minute intervals for intake (or mile marker fuel checkpoints). Then bring a few extra in case the race doesn’t go quite as planned and you’re out there for a little longer. It’s also a good idea to know where all the aid stations are on course, and which products and fluid types will be available as a backup to your planned strategy.