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Calculating Calories - Marathon Trail Run Nutrition

Written by Megan Andersen, Trail Nutrition Coach

A simple way to maintain energy and a happy digestive system.


Covering race and training nutrition for those tackling runs lasting longer than two hours and up to 6 hours.


Keeping in mind that nutritional needs may vary for runs lasting beyond 6 hours or very easy long runs, as there's no one-size-fits-all standard for endurance-running nutrition.


During running, the body utilizes stored carbohydrates and fats for fuel, with the ratio depending on various factors, mainly your effort level, however, there's a limited supply of accessible carbohydrates in the body, approximately 90 minutes' worth of running at a decent effort for most individuals. Beyond that, without additional carbohydrate intake, the body primarily relies on stored fat as fuel.


To run at a consistent pace, you may need a rigorous adaptation process. Otherwise, not being adapted to fat utilization during running can lead to a significant slowdown. To maintain pace and feel energetic, ingesting more carbohydrates as fuel can help. This way, your body will burn both the ingested carbohydrates and some stored fat as you run.


The stomach of an average runner can efficiently digest 150 to 300 calories per hour from specific carbohydrates. However, this varies based on factors like effort, body mass, climate, and carbohydrate type. On the other hand, the average runner burns approximately 600 to 1,000 calories per hour, depending on pace, body mass, terrain, and more. This creates a caloric deficit during long runs, which is normal as the stomach cannot process an equal amount of calories to what you're burning.


The goal, in this case, is to provide it with just enough calories via carbohydrates to help you perform your best.


To optimize your running fuel:

  • The first step in calculating your calorie needs is estimating how long it will take you to complete your run or race.

  • Once you have an estimated running duration, you can calculate your basic caloric requirements.

  • Then create a training/race day nutrition plan: Begin taking in calories within 45 minutes of starting your run or race. Continue refuelling with around 100-130 calories every 20 to 30 minutes.

  • For effective carbohydrate fueling, focus on maltodextrin and fructose.

  • Avoid consuming more than 300 calories per hour, as your body may not be able to digest what you are eating as fast as you are eating it. Basically, aim to eat what helps you feel energetically strong and digestively at peace.

  • Add protein–via products containing amino acids–if it makes you feel better and you have trained with protein products.

  • Don’t add fat to your diet while actually running unless you’re adapted to it.***

  • If you are not keen on eating whole or solid foods while running, pick your poison of gels, chews, powders, or other options. There are a lot of ways to get these calories in, so find the one that works best for you.

***Fat ingestion is advisable mainly for athletes running at very low intensities unless you have undergone the process of adapting to fat utilization at higher speeds, which is not discussed in this blog. However, during runs shorter than six hours, this is not typically necessary. It's important to note that most endurance-running nutrition products do not include fat as an ingredient.


You will want to do some experimenting with different products to find what works best. Some things to consider when choosing trail running nutrition options:

  • How many calories does it contain?

  • How does your body respond to it?

  • How easy is it to carry in your shorts, running belt or pack?

  • How easy is it for you to open while on the run?

Megan Andersen - Trail Nutrition Coach

Proper nutrition at strategic times is vital for maximizing your performance during a marathon distance trail run. Each runner is unique, and personalized nutrition coaching can make a significant difference in your race-day success. If you'd like expert assistance in working out your race day calories and crafting a personalized nutrition plan, feel free to contact me, your Trail Nutrition Coach. Together, we can optimize a personalized fueling strategy for your training and race days.




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