Running On An Empty Stomach: The Pros, Cons, + Health Benefits

One of the challenges with running is trying to decide when in the day to schedule your runs. 

Many people find that running first thing in the morning is ideal from a logistical standpoint but have questions about whether running on an empty stomach is a good idea or problematic.

This leads to common questions such as: Should I run on an empty stomach? Should I run before breakfast? Is running first thing in the morning healthy?

As with many decisions regarding your training, there are pros and cons of running in the morning on an empty stomach. 

In this article, we will explore the benefits and drawbacks of running on an empty stomach.

We will cover the following: 

  • Should I Run Before Breakfast?
  • Is Running First Thing In The Morning Healthy?

Let’s dive in! 

A person running on an empty stomach at sunrise.

Should I Run Before Breakfast?

Generally speaking, running is great for the body and mind no matter what time of day you choose to train.

However, running first thing in the morning can be challenging and not necessarily ideal for every runner.

When you run on an empty stomach, your body has limited glycogen availability, which can compromise your performance, particularly for high-intensity running workouts such as track intervals, hill sprints, and tempo runs, as well as your endurance for long runs.

The body prefers to burn carbohydrates as a fuel source during high-intensity exercise like running because carbohydrates can be oxidized to produce energy at a much faster rate than fats.

However, the body only has limited carbohydrate stores.

A person running in the morning.

According to the Academy of Nutrition and Dietetics, an endurance-trained athlete can store up to 1,800 to 2,000 calories of fuel as glycogen in the muscles and liver, though smaller runners might store closer to 1,500 calories.

When you run first thing in the morning, your glycogen stores will already be partially depleted because liver glycogen is almost entirely used up overnight. This leaves only muscle glycogen, some of which may also be metabolized and used for energy while you sleep.

For this reason, some people find that if they run first thing in the morning on an empty stomach, they feel sluggish and lack energy for faster speeds and longer runs.

Depending on your own personal metabolism, diet, weight goals, training intensity, and training status, you may find that running on an empty stomach compromises the quality of your workouts as well as how you feel. 

However, for some runners, running on an empty stomach is preferable because they struggle with digestive symptoms such as side stitches, cramps, bloating, nausea, gas, or diarrhea if they run too soon after eating.

A person making a heart with their hands and holding it on their stomach.

Is Running First Thing In The Morning Healthy?

There are various pros and cons of running before breakfast.

Some of the benefits of running on an empty stomach include the following:

#1: Running Before Eating Breakfast Reduce Digestive Distress

One of the challenges of running too soon after eating is dealing with various digestive difficulties that come from trying to push your body at a high intensity when you have undigested food jostling around in your stomach and intestines.

Running on an empty stomach can prevent side stitches and stomach cramps, gas, diarrhea, nausea, and bloating while running.

For example, studies have found that nausea when running is more likely to occur when you are exercising at a high intensity on a full stomach.

A person running in a field.

#2: Running On an Empty Stomach May Help You Burn More Fat

Because glycogen stores are somewhat depleted when you run on an empty stomach, your body tries to preserve this “limited resource“ by shifting the relative percentage of fuel you are burning.

Essentially, when you run before breakfast or in a fasted state, you will burn a greater percentage of calories from fat than when you run in the fed state after eating in order to help enhance glycogen sparing for when it is absolutely crucial to generate ATP (energy) more quickly (at higher intensities).

Keep in mind this does not mean that you will burn more calories or lose more body fat by running on an empty stomach. 

Rather, the percentage of calories that you burn coming from fat increases, and the percentage of calories coming from stored carbohydrates decreases.

In fact, some studies suggest that you may burn up to 20% more calories from fat when exercising on an empty stomach.

A person holding up a weigh loss sign.

#3: Running On An Empty Stomach May Support Weight Loss

While we just discussed that running on an empty stomach increases fat oxidation but not necessarily total fat loss, there is some evidence to suggest that running first thing in the morning before eating may actually enhance your weight loss efforts.

For example, even though running in the fasted state doesn’t inherently burn more calories than running after eating, some studies have found that people who exercise on an empty stomach end up consuming fewer calories over the course of the day. 

This may be due to the fact that for some people, running on an empty stomach may suppress the hunger hormone ghrelin, reducing appetite.

For other people, the decreased total daily energy intake may be more of a behavioral shift.

For example, if you start your day out with a hard workout and you are actively trying to lose weight, you might feel like you have already kicked off the day on the right foot, compelling you to be more mindful of your diet for the rest of the day.

This may potentially reduce overeating, lead to more sensible portions, and support better food choices. However, it’s important to note that these results are not necessarily universal.

Some runners find the opposite to be true, such that running on an empty stomach leads them to feel ravenous or filled with “runger” the rest of the day.

This may increase total caloric intake, lead to more instantly gratifying and higher caloric food choices, and stall weight loss efforts.

To that end, some people who run before breakfast feel that they got their workout in, so they overeat to compensate as an “earned reward.”

A person taking their blood sugar.

#4: Running Before Eating May Improve Blood Sugar Regulation

If you have trouble regulating your blood sugar, one of your concerns about running first thing in the morning may be the risk of hypoglycemia or low blood sugar.

If you do have diabetes or insulin resistance, it is important to speak with your healthcare provider before deciding you are going to be doing your workouts on an empty stomach.

That said, most studies have found that exercising on an empty stomach does not cause hypoglycemia, even in athletes with diabetes. Some studies have even found doing so can improve insulin sensitivity and blood sugar regulation. 

There are also potential downsides to running on an empty stomach, including the following:

Two people running over a bridge.

#1: Running On an Empty Stomach Does Not Increase Fat Loss

This is not necessarily a drawback of running on an empty stomach per se, but if you are trying to run before eating in order to enhance weight loss, your efforts are likely futile.

According to research, the resultant fat loss and body composition changes are not affected by whether you exercise before or after eating.

Another review found that exercising first thing in the morning before eating had no appreciable effect on fat loss or weight loss in either direction.

Thus, it is important to consider why you are running on an empty stomach. If fat loss is your goal, there’s no benefit to running without eating. 

Plus, if you are sluggish or lack energy because you have not eaten, you will likely burn fewer calories because you will not be able to maintain the intensity or duration that you could otherwise achieve if you were well-fueled for your workout.

Two people jogging on a track.

#2: Running On an Empty Stomach May Increase Muscle Loss

A greater percentage of energy will come from protein, which comes from catabolizing in skeletal muscle if you run without eating first. This can slow your metabolic rate and decrease strength.

#3: Running On an Empty Stomach May Increase Cortisol

Running when you are not properly fueled can cause a greater increase in the stress hormone cortisol.

This is problematic because chronically elevated cortisol levels have been associated with increased body fat storage, especially in the abdominal area.

Overall, there is no single right answer to “Should I run on an empty stomach? 

You may need to experiment and find what works for you.

To that end, you may find that running without eating first works fine for shorter, easier workouts, but as soon as you get above a certain distance or time or are trying to do a hard workout, you need to have at least a small snack or run after eating to have the energy and strength you need for peak performance.

For some pre-run snack ideas before your morning workouts, click here.

A bowl of oatmeal and bluberries.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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