Fasted Cardio: Does It Burn More Fat, Or Just Hamper Your Performance?

All our fitness and training resources are rigorously vetted by our expert team and adhere to our Exercise Advice Guidelines.

Doing fasted cardio is something that many people either have tried or are considering trying.

Much information is passed around about the potential benefits of working out while fasting, but seemingly less information is passed around about the potential downfalls it could have on your health and performance.

To better understand the pros and cons of fasted workouts, you must better understand their effects on your body. So, is fasted cardio better than cardio after pre-workout snacks?

This article discusses fasted cardio and explores the benefits and downfalls of completing a fasted workout.

We will explore the following:

  • What is Fasted Cardio?
  • Why do People do Fasted Cardio?
  • Benefits of Fasted Cardio
  • Downfalls of Fasted Cardio
  • Should You Try Fasted Workouts?

Ready? Let’s go!

Fasted Cardio: Does It Burn More Fat, Or Just Hamper Your Performance? 1

What is Fasted Cardio?

Fasted cardio is the act of engaging in cardiovascular activity without having eaten in recent hours. For most people, this means doing a workout in the morning without eating breakfast first.

When you complete fasted cardio, this means doing some type of aerobic activity essentially on an empty stomach. This could mean waking up and going on a run, brisk walk, bike ride, or swim before consuming anything. 

A “fasted” state typically refers to having gone without food overnight or for a period of 8-12 hours. 

Why Do People Do Fasted Cardio?

Many people believe you are more likely to burn fat when you do cardio workouts in a fasted state.

This is because, unlike when you are fed, your glycogen stores are depleted. Having depleted glycogen stores means that you do not have any stored energy from carbohydrates ready to be utilized. 

A person running on a treadmill.

When that happens, your body needs to turn to fat stores.

Some people’s bodies are more efficient than others at utilizing fat for energy over carbs. People who do fasted cardio do so for a variety of reasons, but some of the main reasons are due to specific athletic goals or weight loss. 

For athletes who plan to compete in multi-day athletic events like stage races and ultramarathons, effectively utilizing fat as energy can be really beneficial.

These athletes often make an effort to become fat adapting in the months leading up to their event so that if they have trouble consuming food, their bodies can turn to their fat stores. 

Some people believe fasted cardio is a great way to improve caloric burn and melt away fat resulting in weight loss. While doing fasted workouts may contribute to weight loss, there are alternative methods that are proven to be either as effective or more effective. 

Women should be particularly cautious when using fasted cardio for weight loss due to the impact fasting can have on their hormones. Hormone disruption can ultimately cause weight gain and even lead to injury if you are not cautious. 

A person on a rowing machine.

Benefits of Fasted Cardio

Whether or not you will benefit from fasted cardio can depend on many factors.

Things such as individual metabolism, how hard or often you exercise, overall caloric balance, and your ability to adhere to an exercise routine over time are all important when it comes to achieving sustainable results, and whether or not you do fasted cardio may be a very small piece of the success puzzle. 

#1: Weightloss and Insulin Control

People who believe that doing fasted cardio is beneficial feel strongly that exercising in a fasted state will increase fat-burning ability and, as a result, weight loss.

This belief comes from the idea that enhanced fat oxidation occurs as the body utilizes fat for energy instead of glycogen stores. 

While some research does show that there are short-term positive effects on insulin control for people who work out in a fasted state, there is not enough evidence to prove definite long-term benefits.

Being less sensitive to insulin is beneficial for overall metabolic health, but having this response to working out in a fasted state may not happen for everyone. 

Two people running.

#2: Improved Endurance

Many people who run and do other cardio activities while fasted feel that doing so improves their endurance. They may feel this way because of potential adaptations their bodies have made to burn fat as their primary energy source during exercise. 

However, becoming fat-adapted takes time.

If you stay consistent with training and practicing proper nutrition during this time, these things can also improve endurance. This makes it hard to determine which factor most impacts improved endurance over time. 

#3: Convenience and Preference

Another reason fasted cardio may work for someone or benefit them is due to time and preferences.

Some people do not have time to eat before a workout if they work out in the morning. It is also possible that food may not sit well with them if they eat before a workout.

Choosing to do fasted cardio eliminates both of these issues. 

A person on an exercise bike.

Downfalls of Fasted Cardio

Doing a fasted workout may not be a good choice for everyone.

Individual metabolisms and energy levels vary greatly, so when making a big change, like going from fueling before a workout to not fueling, you should practice caution and be sure to understand the potential risks. 

#1: Medical Conditions and Medications

If you struggle with low blood sugar levels or experience dizziness spells or bouts of fatigue when you go too long without eating, doing cardio in a fasted state is not a good idea.

Any person with health issues that may cause problems with energy or blood sugar levels should not try a fasted workout without consulting their doctor. Certain medications may also make this riskier. 

#2: Negative Impact on Performance 

Working out without eating could have a detrimental effect on your workout. It may be harder for you to reach your desired intensity when doing fasted running, and your overall performance may come up short of what it typically does. 

When you work out on an empty stomach, your body cannot get energy from the typical resource it often relies on, which may result in reduced stamina, strength, and endurance during your fasted workouts.

Some people’s ability to exercise at a high intensity or maintain a consistent training pace when fasted may be more severely impacted than others. 

A person on an elliptical machine.

#3: Potential Loss of Muscle Mass

When you go into a workout fasted, and your body is not used to it, it may turn to protein as an energy source.

In order to utilize protein as energy, your body may end up breaking down your muscles. If you have goals of building or maintaining muscle mass, this can be detrimental to your goals. 

Eating a protein-rich pre-workout meal or snack can help reduce the likelihood of your body utilizing protein as a fuel source which, of course, is not part of the fasted-workout protocol.

If you choose working out while fasting, you should be sure to eat a snack or meal containing at least 20 grams of protein and a healthy mix of fats and carbs within 30 minutes of completing the workout. 

#4: Delayed Recovery Time

Doing fasted workouts may cause a delay in the replenishment of glycogen stores due to starting in a deficit.

It is important to replenish these stores promptly after your fasted workout. When you workout fasted, you are in an even bigger glycogen deficit than you would be if you worked out in a fed state. 

Your body relies on glycogen along with other mechanisms to begin repairing the damage done during a workout.

Glycogen replenishment may not be the main driver of muscle repair, but it does play a crucial role in restoring energy levels and helping you get ready for your next workout. 

A person running.

#5: Increased Perceived Effort

Going into a workout without eating may set you up for a particularly long-feeling or hard workout. A workout that tends to feel easy for you may feel more challenging thanks to empty glycogen stores.

When your workouts feel more challenging than usual, you may feel less motivated and get less joy out of it, which can be detrimental to your progress and negatively impact your ability to reach your goals.  

Should You Try Fasted Workouts?

If you want to try fasted workouts, chat with a healthcare provider, dietician, or fitness professional to get more information on if fasted cardio is better than exercising after eating for you specifically.

During these conversations, your individual and specific circumstances are considered, and make sure to mention your current or past medical conditions. 

Before diving into fasted workouts, take some time to weigh the potential pros and cons.

Assess whether or not the potential risks and benefits align with your goals and overall well-being. At the end of the day, the most effective exercise and weight loss strategy is different for everyone. 

A person running up stairs.

Takeaways

When trying any new diet or workout, it is crucial that you listen to your body and make changes as needed to respond to your body’s needs.

Staying consistent, monitoring calories in versus out, and staying active are the best ways to achieve fitness goals and maintain success long-term. 

If you want to give fasted running a try, check out our guide on Fasted Running: How To, Benefits, + Drawbacks

Photo of author
I am a UESCA-certified running coach, psychology PhD student, and competitive obstacle racer and trail runner. Once 100 pounds overweight I found fitness and fell in love with an active and competitive lifestyle. My passion for inspiring others and fitness come together seamlessly in the world of writing where I get to share the thing that changed my life. In my free time I enjoy spending time with my family, my dogs, as well as baking and cooking.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.