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How many calories should I eat during an ultra?

Running an ultra distance is a physical endeavor that requires tremendous amounts of work and discipline. Runners can spend months and sometimes years training their mind and body to overcome the challenges brought upon by the sport. A key element to successfully complete an ultra marathon or an ultra trail is a proper nutrition plan, however this can be a challenge in itself.

Unfortunately, there is no “one-size-fits-all” nutrition plan; everyone is different and your nutrition needs will likely differ from those of your peers. The only way to figure out what works best for you is to get out there and experiment. Nonetheless, there are general concepts and guidelines that you can follow and learn from when building your nutrition plan.

The following article was written to help you tailor your nutrition strategy and optimize your performance on race day.

Why is eating while running difficult?

The simple task of eating can become quite daunting for athletes running ultra distances. It is common to hear runners complain about symptoms like nausea, gastric reflux, the urge to defecate, and many more… but why?

During exercise, a process known as thevascular shunt mechanism is activated in your body. Quite simply, your cardiovascular system will redistribute your blood so that more of it goes to your working muscles and less of it goes to your other body organs such as your digestive system. This intrinsic process plays a role in increasing your sensitivity to the foods you ingest during your run.

In addition a common cause for poor digestion during prolonged physical effort is dehydration. A lack of water intake and loss of minerals through sweat can cause ulcers and acid reflux because the stomach does not have enough resources to produce the digestive acids your body requires to break down food. In addition, dehydration plays a role in decreasing the blood circulation to your digestive system even more. Hence, it is crucial to pay attention to the hydration portion of your nutrition plan to avoid discomfort during your ultra marathon or your ultra trail.

On top of it, running creates a lot of bouncing up and down, which can jostle your organs and push food through your digestive tract faster than when you are kicking it back on your couch at home. This can often lead to a lot of discomfort in your gut.

With all of this being said, even though your digestive system is compromised while running and you cannot expect to eat a full meal, you still need to get some calories in you to keep on going and finish your race...

Ultra trail runner Näak ambassador

How many calories can my body handle?

The average runner will burn between 600 and 1000 calories per hour while running. However, your body is only capable of absorbing 1g of carbohydrates per minute while you undergo physical exertion. For every gram of carbohydrates you eat, you get 4 calories. Hence, you can eat about 240 calories per hour. The exact amount of calories will depend on different factors. For instance, people who are larger will need to consume more calories than those who are smaller. In addition, people who are completing long, strenuous runs will need more calories per hour than those doing shorter, easier runs. With this being said, everyone is different and you should aim to eat 200-300 calories per hour based on what feels right for you.

What fuels my body when I am running?

As mentioned above, runners typically burn 600-1000 calories per hour while running, but only manage to digest 200-300 calories per hour. This makes running a calorie-deficit sport and means that ultimately you will not be able to consume enough carbohydrates to feed your effort… so how is it possible to keep on going?

Your body is capable of storing a sufficient amount of carbohydrates to fuel your body for approximately 90 minutes of running. The carbohydrates available to use as energy are the following: blood glucose, muscle glycogen, and liver glycogen (glycogen being a chain of glucose that can be broken down by your body). Your body will also turn to fat and protein, both of which can be used as fuel during running. However, this requires an intense adaptation process which might cause you to slow down. On the basis of thereof, when you are covering long distances it is important to supply your body with enough carbohydrates to maintain your pace and feel energetic. Ideally you want to give your body glucose; the simple sugar that fuels your body by providing it with easy-to-digest energy without making you feel sick.

What should I eat during my ultra and when?

As mentioned earlier, on any run that lasts over 60-90 minutes, you must plan to bring something to eat on your outing. While you may have enough energy to cover that first portion of your ultra marathon without eating, you shouldn't wait to be fatigued before you start getting some food in. The longer you run, the more pressure you are putting on your body, and the harder it gets for you to eat, so you want to start eating about 45 minutes into your run. From there try to eat something every 30 minutes. Setting an alarm is a good way to remind yourself to eat something! By eating little and often, you will reduce your risk of having digestive issues and keep blood sugar levels more stable to reduce your risk of bonking; which is mainly caused by the depletion of glycogen stores in the liver and muscles.

For the first 4 hours of your ultra distance, you should be able to maintain your energy levels with a steady intake of carbohydrates. There are many food and beverage options available for you to get those carbohydrates in, for instance energy bars, gels, gummies, purees, hydration drinks, energy drinks, and so on so forth. Just make sure you practice your nutrition plan before race day to train your body to digest the foods you chose.

After 4 hours, you should start adding some protein and fat to your nutrition. A general rule of thumb is to replace 25% of your calories coming from carbohydrates with calories coming from protein and some fat. This will help you ensure steady energy levels for the rest of your run, help reduce muscle breakdown, and add some variety to your diet which is always pleasant on long runs. Good examples of foods you can eat that offer the 4:1 carbohydrate/protein ratio are peanut butter and jelly sandwiches or Näak’s ultra endurance energy bars which were designed to keep you energized during your ultra marathon and your ultra trail runs.

What about hydration?

An important component of nutrition is hydration. As you are running, your body is producing sweat as a cooling mechanism to maintain your body temperature. Through sweat, you will be losing an important amount of electrolytes, which are ionized minerals that play a functional role in your body. Hence, it is important to hydrate and supplement with electrolytes during those long runs to avoid nausea or cramps.

Calculating your sweat rates

Runners’ sweat rates can vary from 0.5-3L/hour based on the person and external factors such as temperature, humidity, running intensity, clothing choices, etc. The best way to establish how much you should be drinking is to determine your own sweat rate. To do so, weigh yourself in the nude, run for 1h without drinking or eating anything, then weigh yourself in the nude again. For every 1 lbs weight loss, you have lost 1 L of liquid.

Ideally you should calculate your sweat rates on a number of occasions and in various conditions to get to know your body and develop proper hydration habits.

Should I drink all the fluids I lose in my sweat?

At first glance it might seem like a good idea to drink and replace 100% of your fluid loss. However, this would mean drinking beyond your body’s natural thirst instincts and may put you at risk of hyponatremia; low blood sodium levels, which can be dangerous. Overdrinking can also have an undesirable sloshing effect on your relatively empty stomach so you’ll want to avoid that.

Instead, you should replace some, but not all your fluid loss. Your goal should be to drink enough during your run to prevent excessive dehydration and excessive changes in electrolyte balance to prevent compromised performance. This can be done by drinking water, having electrolyte tabs, salt tablets, etc.

To sum it up, your body can handle a certain level of dehydration which sits at about 2% body weight loss from water deficit.

ultra marathon runner

Photo credit: Running Addict


This article gives you a basic idea of general concepts and guidelines that you can follow and learn from when building your nutrition plan to help you optimize your performance on race day. To sum it up, here are the important takeaways:

  • Everyone is different, trial and error is the best way to find out what works for you.

  • Eat early on in your run, and eat frequently.

  • Aim to ingest 200-300 calories/hour with food/hydration that makes you feel energized without digestive issues.

  • Many factors will influence your energy needs, what you can stomach to eat, your sweat rate, your salt levels, and your heart rate. For instance, running intensity, pace, climate, terrain, altitude, incline, body mass etc. Listen to your body and be ready to problem-solve and adapt if need-be.

You have discovered the Näak Ultra Energy Bars in this article and would like to try them? Don't hesitate any longer, find all our flavors here!

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