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This Marathon Nutrition Calculator Will Dial in Your Fueling Strategy

by Zach Nehr

Blog ▸ This Marathon Nutrition Calculator Will Dial in Your Fueling Strategy

Eating during a marathon is the definition of “easier said than done.” What are you supposed to eat, how much, how often, and what about water versus electrolytes?

We’re going to answer all those questions and more in this article. First, you’ll plug your numbers into our Marathon Nutrition Calculator. Then, we’ll guide you through the details of creating a nutrition plan for marathon training and racing. By the end of this article, you’ll know how to execute the perfect marathon nutrition strategy on race day. 

Plug Your Numbers into the Marathon Nutrition Calculator

Our Marathon Nutrition Calculator is based on your body weight and the pace you will run. The calculator suggests that you consume roughly 25% of your burned calories during the marathon. You can learn more about this nutrition strategy in “The Performance Zone: Your Nutrition Action Plan for Greater Endurance & Sports Performance,” by John Ivy and Robert Portman. 

Running Nutrition Performance

One of the keys to marathon nutrition performance is that it involves much more than the run itself. Here, we’re going to take you step-by-step through the crucial fueling windows for a marathon. 

Marathon Nutrition Timing

The fueling begins 15-30 minutes before the race start. Depending on the marathon’s start time, you don’t necessarily need to consume a full breakfast before the race. Assuming you have carb-loaded the day before the race, your body can store up to 2000-2500 calories overnight.

You should still have a carb-based breakfast on race morning to make sure that your carbohydrate stores are completely topped off. Ideally, you should have this carbohydrate-based breakfast four hours before the race to give your body plenty of time to digest the food. For an 8:00 am race, that means having breakfast at 4:00 am. Many runners will go back to bed or even take a nap between their early morning breakfast and the start of the race.

Having breakfast before a marathon creates a buffer – like nutrition insurance – which provides you with some extra carbohydrates if you under-fuel during the race.

Whether you have time for a whole morning meal or not, you should be fueling with 20-50 grams of carbohydrates 15-30 minutes before the race starts. These carbs can be in the form of a sports gel or energy drink, and liquids are best. 

How Often to Eat During a Marathon

Once the race has started, your nutrition window – or how often you eat or drink – comes in 17-30 minutes increments. Studies have shown that carbohydrates in liquid form are the best food to consume during a marathon for most runners

The amount and frequency of carbohydrate fueling depend on the length and intensity of the event, as well as the runner’s body weight. An average marathon runner, for example, may target 30-60 grams of carbohydrates consumer per hour during a marathon. 

Highly-trained runners may consume even higher amounts of carbohydrates in 80-100 grams per hour.

How to Use the Marathon Nutrition Calculator

We’ve alluded to many of the significant factors affecting marathon nutrition, but now it’s time to piece it together. The number revealed by the Marathon Nutrition Calculator is more than just a number – you cannot fuel your marathon with equal amounts of chocolate cake, sports gels, or broccoli and expect the same result.
Not all calories are created equal when it comes to marathon nutrition and fueling your training session. Read on through the rest of this article, and soon you’ll be able to put together your marathon nutrition plan.

Here is what we’re going to cover in the rest of this article:

  • Calories Burned While Running
  • What to Eat During a Marathon
  • Ideal Race Nutrition
  • Fueling Training Sessions
  • Running Weight Performance
  • Pro Tips for Marathon Nutrition

Calories Burned While Running 

man, jogging, exercise

How many calories you burn while running depends on three main factors: duration, intensity, and body weight. 

How Many Calories the Average Runner Burns

The longer you run, the more calories you will burn. An average runner will burn anywhere from 400-600 calories per hour during an easy-to-moderate run.

The harder you run, the more calories you burn, and the fastest runners in the world can burn over 1000 calories per hour. Adjusting your fueling based on your run intensity in training is essential. For an easy 10-mile run, you may only need a gel or two. But if you go out and do 10 miles at race pace, you might need 4-6 gels to fuel your workout. 

Lastly, body weight significantly affects how many calories you burn while running. The lighter you are and the less body weight you have, the fewer calories you will burn. Conversely, larger and heavier runners will burn more calories than smaller runners. 

Go back up to our Marathon Nutrition Calculator and try changing your weight. You can move it up or down to understand how much weight makes a difference in marathon nutrition.

Before diving into the numbers, let’s talk about the kinds of foods you should eat during a marathon. 

What to Eat During a Marathon

Liquid sources of calories are best for marathon training and racing because of the pounding effects of running. It can be hard to stomach solid food on the run, and it may take longer for your body to absorb the calories, too. 

Gels are one of the most common sources of carbohydrates during a marathon. They are small, easy to use, and can be consumed in two seconds. There’s no chewing required, and in a matter of seconds, you will have another 20-30 grams of carbohydrates flowing into your bloodstream.

Many runners consume sports drinks, electrolyte mixes, or sodas during a marathon. Each drink has its own mixture, which can be watered down or made even more concentrated. Electrolytes are vital on hot days, while the carbohydrates from a sports drink or soda help keep your energy levels full.

In most cases, runners should separate their fluids from their calories. If you start experiencing stomach distress, yet all your calories are coming from liquids and bottles, the risk becomes two-pronged. 

On the one hand, if you continue drinking your fluid calories, you could seriously upset your stomach and experience cramps, GI stress, or worse. But on the other hand, if you stop taking in your liquid calories, you risk emptying your calorie tank and bonking. 

The best solution is to separate your fluids from your calories. For most runners, the best marathon fueling strategy is to consume their calories in liquid gels while also consuming water or a low-calorie electrolyte mix

Ideal Race Nutrition 

This is where it all starts coming together – we know how many calories we need to consume during the marathon, the type of foods we should consume, and how to separate your fluids from your calories.


Ahead of race day, you should be able to lay out your race-day nutrition with the exact amount of total calories you need for the race. You may be carrying some food, but you should also know what will be available at the aid stations along the marathon course. If you don’t have to take the extra weight, don’t.

Most of your calories should come from liquid sources such as energy gels. You should consume one of these gels every 17-30 minutes or once every couple of miles. This will give your body enough time to process the carbohydrates while constantly filling up your glycogen stores.


You shouldn’t need any solid food during a marathon, as this will be difficult – and maybe even painful – to process mid-run.


Most of your hydration should come from electrolyte mixes and some water. Electrolyte mixes are best for performance but can be difficult to stomach for long periods. If you feel your stomach starting to turn, switch to drinking water until your stomach resettles, and then go back to electrolyte mix.


Low-calorie electrolyte mixes not only provide fuel and hydration but also increase absorption of carbohydrates. The higher your absorption, the more quickly you can access the 30+ grams of carbohydrates from a gel. This is especially important during a marathon when you want to be able to access carbohydrates as quickly as possible.

Low-calorie electrolyte mixes not only provide fuel and hydration but also increase absorption of carbohydrates. This is especially important during a marathon when you want to be able to access carbohydrates as quickly as possible. The higher your absorption, the more quickly you can access the 30+ grams of carbohydrates from a gel. 

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Example Marathon Nutrition Plan 

  • 15-30 minutes prior to the start
    • 1 gel and a mouthful of water
  • Every 17-30 minutes: 
    • 1 gel and a mouthful of water or electrolyte mix (<30 calories per serving)

You also need to practice your calorie intake in pre-race training sessions in order to train your gut. Like any other muscle in your body, your gut needs to be trained to take on and absorb heaps of carbohydrates in the middle of a hard run. Neglect gut training and you may find yourself stopping on the side of the road (or sprinting to the toilet) in the middle of your marathon. 

Fueling Training Sessions 

In the 6-12 weeks leading up to your race, you should be practicing your race-day nutrition strategy in training. Your training sessions should be fueled in the same way as racing, but with some adjustments for volume and intensity. The vast majority of your training sessions will be done far below race pace, which means you will be burning fewer calories. 

Use our Marathon Nutrition Calculator to practice your nutrition strategy in training, and pay attention to your body during these sessions. If you get an upset stomach, try eating a little bit less during the next training session. But if you start fading near the end of your workout, you might need a little bit more fuel onboard.

How many calories you consume in a marathon training session depends on the session’s duration, intensity, and body weight. It may take some practice to find the right foods and gels for your stomach, but that’s why you practice in training instead of trying something new on race day. 

Before longer or low-intensity training sessions, it is acceptable to consume more fat and protein in your diet. Ahead of hard workouts and especially race day, your diet should consist of mostly carbohydrates which are the best fuel source for high-intensity exercise. 

Running Weight Performance 

With all this talk about eating, fueling, running, and food, it is inevitable that we talk about ideal running weight. Covered in this post here, we mentioned our Running Weight Calculator which is more for fun than genuine use.

For the vast majority of athletes, your ideal running weight is roughly 10 lbs heavier than what is suggested by our Running Weight Calculator. It can be tempting to lose weight in the hope that it will make you faster, but this plan will eventually fall apart. Weight loss is not always a good thing.

If your calorie expenditure is greater than your calorie consumption, you will start losing weight and you will no longer be able to fuel your workouts. Instead, it is best to prepare a meal plan that contains a mix of carbohydrates, healthy fats, and protein to fuel your workouts.

You shouldn’t be shedding pounds in the middle of the season. Rather, your body weight should stabilize as your training load and performance increase.

Pro Tips for Marathon Nutrition

You know what they say about the best-laid plans… Marathon nutrition is not as simple as writing a plan and executing it. There are lots of things that could go wrong – the weather might change, you might forget a packet of gels, or you might start bonking with 7 miles to go. 

But if something goes wrong, that’s no reason to give up – there are a number of things that you can do to get back on track. Here are our pro tips for marathon nutrition: 

  • If your stomach starts to go awry, switch to drinking water instead of any electrolyte or flavored mix. This will change the osmolality in your stomach – once your stomach feels better (which it will), then you can switch back to drinking electrolytes
  • Carry a Crampfix or HOTSHOT in your pocket in case you start cramping – this will help you reset both physically and mentally in the event of a cramp
  • If you are beginning to fade, have a soda such as a Coke which will provide you with a quick caffeine shot and a boost of energy 
    • Once you have your first Coke, stay on it. Don’t go back to your previous nutrition strategy or you’ll run the risk of losing energy, upsetting your stomach, or feeling erratic from going on and then off of caffeine.

Conclusion

Use the Marathon Nutrition Calculator to create a nutrition plan for your next marathon. Remember to start fueling 15-30 minutes before the race, and then continue fueling every 17-30 minutes through the race. Aim to consumer mostly liquids such as energy gels, plus electrolyte mix and water. You can drink water to help reset your stomach if it starts to turn in the middle of your run.

Don’t forget to practice your fueling strategy in training and adjust based on the session’s duration and intensity. Check out the resources below, and “The Performance Zone: Your Nutrition Action Plan for Greater Endurance & Sports Performance” for more information.

Sources

Zach Nehr

Zach Nehr

Zach has a degree in Exercise Science and Psychology. He is a certified coach, Cat 1 cyclist, and is a freelance writer having been published in many of the worlds largest endurance sports publications.