Pros And Cons Of Running On An Empty Stomach

Some people love running and prefer doing it as their daily exercise. But is it okay to run on an empty stomach? What could be the pros and cons of running on an empty stomach? If you are someone who loves running, then you must go through this article. It talks about some of the pros and cons of running on an empty stomach.

The Science Behind Running On An Empty Stomach:

Our body does not like to burn its fat reserves, rather it wants to use what is accessible easily. After fasting for 8-12 hours, like in the case of overnight sleeping, the body automatically begins to burn the carbohydrates that are stored in our muscles and liver for energy. Once the body runs out of carbohydrates, the body’s stored fat begins to burn. But, it takes a long time for the stored fat to convert into energy.

If you are planning to go for a moderate or light run for less than 90 minutes, then your body should be able to turn fat into energy without you having to eat before running. But, the body cannot mobilize the stored fats while burning enough to sustain energy during your high intensive runs. This clearly means that once your body gets short of carbohydrates, it would be no longer be able to continue working at that intensity. So, if you want to go for a long or intense run, know that your performance will be suffering from fasting before your run.

Runners who run in the morning, mostly prefer not to eat before their workout. Running on an empty stomach, usually after 6-8 hours of overnight fasting is sometimes referred to as “fasted running”.

Your glycogen levels are low if you have not eaten. Glycogen is the storage form of carbohydrates. Our body primarily uses glycogen for energy.

If running on an empty stomach is effective or safe, it depends on your body, your fitness goal, and your workout.

Though some runners find fasted running quite safe and effective, there are also some drawbacks of running on an empty stomach. Below, let’s explore the pros and cons of running on an empty stomach.

Pros Of Running On An Empty Stomach:

Running on an empty stomach has several potential benefits. Let us find out some of them.

It Might Increase Fat Burn:

One of the pros of running on an empty stomach might be that it might increase fat burn. Running on an empty stomach or fasted running, has positive effects on your body fat burn. Since your carbohydrate stores are low when you have not eaten, your body uses more fat for energy. This in turn results in higher fat burn or oxidation.

A small study of 10 male participants conducted in the year, 2015 showed that that exercise increased fat burn or fat oxidation over 24 hours when the workout was done before eating in the morning.(1)

The same results were also found in another small study of 2017 with 9 female participants.(2) As per the researchers of the study, it was found that exercise increased fat oxidation or fat burn because of the body’s response to low levels of carbohydrates. The lack of carbohydrates is known to stimulate genes controlling fat oxidation.

However, the research is conflicting. It was found from another study of 2018 that fasting has resulted in less fat burn after exercise than taking a meal of carbohydrates or protein before the workout.(3) A review of 2020 taken from 71 studies, did not find an appropriate link between fasted endurance training and increased fat burn or fat oxidation.(4)

It is necessary to have more research on this.

It Helps In Reducing The Digestion Problems:

It is common to experience various digestive problems during prolonged exercise. Some of the digestive issues could be upset stomach, intestinal cramps, vomiting, nausea, or diarrhea. Such symptoms generally affect runners who run long distances or athletes who train for a long time. So, if you are prone to exercise-induced digestive problems, it might be ideal to run on an empty stomach.

Running On An Empty Stomach Might Improve Aerobic Endurance:

There is some evidence that running or training on an empty stomach might improve aerobic endurance.

In a small study of 2010, it was found that fasted exercise was linked with higher VO2 max. The maximum oxygen uptake during any intense physical activity is known as VO2 max.(5) This is a measurement of aerobic endurance and overall fitness.

But, the study is quite old and only involved 14 participants. However, more research is required.

It Helps In Controlling Your Energy Intake:

Running on an empty stomach also helps in controlling your energy intake. If you want to lose weight, fasted training might help in controlling your energy intake.

In one small study of 2016, 12 participants who were running on an empty stomach, used less energy over 24 hours.(6)

One more study conducted during 2019 that included 12 male participants has found that fasted exercise lowered energy intake over a time of 24 hours.(7) The researchers attributed this to the liver, which even stores glycogen.

When the levels of your blood and muscle glycogen get depleted, your body taps into the liver glycogen stores. As per the researchers, this affects your body’s energy intake via the liver-brain neural network.

Cons Of Running On An Empty Stomach:

There are also some cons of running on empty stomach:

It Increases The Risk Of Injury:

As the energy stores of your body decline, you are more likely to feel fatigued. There is an increased risk of injury during physical activity when you are experiencing fatigue.
Moreover, the brain requires glucose to function properly. This is particularly important when your body is also making use of glucose to fuel the muscles of your body.

If you run on an empty stomach, your brain might not get enough energy. It might be hard for practicing proper form and pay attention to your surroundings.

Reduced Training Intensity:

There is also one more cons of running on an empty stomach. It can reduce your training intensity.

Although the body can use fat as the body’s fuel for energy, it is not sustainable. Fatigue sets in when your fat stores fail to meet the demands of your run. This would make it hard for you to maintain a high intensity or pace.

An older study of 2010 has shown that running on an empty stomach was linked with lower endurance for 10 male participants.(8)

According to a review of 46 studies, it was found that exercising after eating improved prolonged aerobic performance.(9)

It Increases The Risk Of Certain Conditions:

A fasted exercise is not right for everyone. If you suffer from diabetes, then running on an empty stomach might result in low blood sugar or Hypoglycemia.

Is a chance of developing exercise-induced hypoglycemia if you are taking diabetes medications, such as insulin. To remain safe, you should always check your blood sugar and eat something before running. Similarly, if you suffer from Addison’s disease, then fasted running can cause dangerously low levels of blood sugar.

So, if you have any health issues, make sure that you ask your doctor to know how to safely exercise.

It Is Ineffective For Long-Term Weight Loss:

It is found from some research that exercising on an empty stomach increases fat burn. However, it might not be ideal for long-term weight loss.

As per a study of 2014 that included 20 participants, exercising before and after eating resulted in similar rates of weight loss.(10) These research findings suggest that working out on an empty stomach does not result in any significant changes in your body composition.

This is because of the way our body regulates its fuel source. During a fasted run, when we burn high amounts of fat, our body compensates by reducing fat burn later on. Instead, the body utilizes more glucose.

It Can Cause Overeating:

Running on an empty stomach can cause overeating. When you do not eat anything before running or any workout, your body will keep craving calories after running or workout. You might feel more hungry and eat more throughout the rest of the day for making up the energy supplies that were depleted when you were running. You would start eating more calories or overeat.

It Does Not Promote Fat Burning:

It is a myth that running on empty stomach results in fat burn. The theory behind it is that if you do not offer any fuel to your body before you run, your body would turn to fat stores for energy immediately. But, since you have to run at a lower intensity, you won’t be burning much fat. If you are looking for weight loss, you will burn more calories, both after and before running with higher-intensity exercise.

It Might Lead To Muscle Loss:

Running on an empty stomach might lead to muscle loss. Cortisol hormone is produced by your adrenal glands and that controls basic functions, such as blood glucose and the stress response.

At high levels, this hormone promotes protein breakdown in your muscle cells. This increases muscle weakness and muscle loss.

In the early morning, our cortisol levels are highest. Moreover, a study conducted in the year 2015 found that morning exercise after fasting overnight, increases the levels of cortisol.(11) So, this means that if you run on an empty stomach, which is done usually in the morning, it could affect your muscles negatively.

Final Words:

So, we now know that there are pros as well as cons of running on an empty stomach. However, it is better to eat a light snack before running, as it gives your body the required fuel to exercise efficiently and safely. But, if you prefer running on an empty stomach, then stick to light or moderate running and take a break whenever you feel lightheaded.

We must also mention that everyone is different and we must listen to our body and run accordingly. Talk to your doctor for the safest options if you are trying to run on an empty stomach.