Fasted Cardio:  Does it Work?  And Should You Do it?

Fasted Cardio: Does it Work? And Should You Do it?

Many people swear by fasted cardio. In theory, working out in a fasted state should burn more fat. With no fuel for the body to burn, it would have to turn to fat for energy. This would enhance fat loss and body composition. It makes logical sense and sounds pretty good, but does fasted cardio really work?

What is Fasted Cardio?

Fasted cardio is cardiovascular training in a fasted state; meaning the body has digested all food and either used or stored away all macronutrients from your last meal. A fasted state results in low insulin levels, and is generally around 4-8 hours after your last meal for most people, depending on your metabolism. For this reason, most people choose to perform fasted cardio after sleeping through the night, usually early in the morning.

How Fasted Cardio is Supposed to Work

fasted cardio training

In his 1999 book “Body For Life,” bodybuilder Bill Phillips discussed the idea of fasted cardio as the ultimate method for enhanced fat loss and body composition. He is generally credited with introducing the idea of fasted cardio.

With the body in a fasted state, all food has been digested and either used or stored away. The best example of this is when you wake up in the morning. Insulin levels are low, and the body is using fat as it’s primary energy source.

According to proponents of fasted cardio, exercising in a fasted state will force the body to use fat as an energy source, as no carbohydrate will be available in the bloodstream.

Benefits of Fasted Cardio

According to research, there are certain benefits to training in a fasted state. Whether it’s a good idea for you or not really depends on what you’re trying to achieve.

Improved Endurance Exercise Performance

One Study found that 6 weeks of regular cardiovascular training in a fasted state improved Metabolic Flexibility in subjects. This means that performing fasted cardio resulted in the body improving it’s ability to use fat as fuel during exercise.

The study also showed that training in a fasted state prevented a drop off in blood glucose levels during exercise. These adaptations would likely result in improved performance in endurance exercise.

Does Fasted Cardio Boost Fat Loss?

burn fat

While the above study was encouraging, it’s not so clear cut.

A huge part of the fat being used as energy is coming from intramuscular fat deposits. This fat, stored within our muscle tissue, has little effect on how we look. It’s not the type of body fat most of us are trying to get rid of.

Another study from 2014 showed no difference in body composition or fat loss between a fasted cardio group and a group eating a meal before exercise.

So, do you burn more fat with fasted cardio? Maybe, but a huge percentage of it isn’t the fat you’re interested in getting rid of.

Problems With Fasted Cardio

There are several reasons why fasted cardio doesn’t work the way we’d like it to. While it seems like a logically sound method for burning extra fat, the human body is very complex. It doesn’t always work the way we’d like it to.

All 24 Hours Count, Not Just Your Workout

Even if a fasted cardio workout did burn more fat, it only represents a small portion of your day. All 24 hours count, not just the hour or two you spend in the gym.

Thermic Effect of Food and Exercise (“Afterburn”)

Taking in food before a workout has been shown to increase the Thermic effect of exercise after the workout. This means that fueling before you exercise increases the amount of calories (including fat) you’ll burn throughout the day. (Also known as the “afterburn” effect of exercise.)

Muscle Loss With Fasted Cardio

Training for one hour in a fasted state has been shown to more than double muscle loss compared to training while fueled. Approximately 10% of calorie expenditure can come from breaking down muscle protein (muscle gluconeogenesis, if you like fancy terms).

If you care at all about gaining or maintaining muscle mass, fasted cardio is a poor method, as you are literally forcing your body to burn away muscle tissue.

Exercise Intensity Suffers

fasted cardio and exhaustion

Performing high intensity interval training (HIIT) has been shown to help you speed up fat loss when compared to steady state cardio. Studies have shown that HIIT can improve fat loss by 28% compared to steady state training.

Unfortunately, performing high intensity training in a fasted state is never going to be optimal.

With the body in a hypoglycemic state (low blood sugar), and low on fuel, exercise intensity will suffer. Part of the benefit of high intensity training is the post-exercise increase in metabolic rate, where you’ll be burning more calories all day long. You sacrifice part of this benefit when you train on empty.

Trading solid HIIT sessions for the sake of using fasted cardio just isn’t optimal. Attempting to perform high intensity workouts without fuel is a poor choice, as you’ll be stressing your body out and can impair your recovery abilities as well.

Read: 15 Biggest Weight Loss Mistakes to Avoid

What Works Better Than Fasted Cardio?

lift weights for fat loss

When it comes to burning fat, people have cardio tunnel vision. Cardio has become synonymous with fat burning, and many people mistakenly believe that cardio alone will get them leaner and meaner.

But if you focus only on cardio, you’re missing out on a huge piece of the puzzle.

Lift Weights to Burn More Fat!

Your muscles are the metabolic engine of your body. Metabolism takes place inside your muscle tissue. They are essentially fat burning machines.

More muscle requires more energy. Resistance training can boost your resting metabolic rate, leaving you burning more calories all day, every day.

Variety and Balance are the Best Option

Using some variety is the most effective way to burn fat and get leaner without losing muscle mass in the long run. The following would be a pretty good approach to losing fat and maintaining or gaining muscle.

  • 1-2 HIIT workouts per week
  • 2-4 steady state cardio sessions per week
  • 2-3 Resistance Training sessions per week
  • High protein diet, cut out the sugar and limit your carbs, focus on whole foods.

Conclusion: Should You Use Fasted Cardio?

As we said earlier, it really depends on you and what your goals are.

If your goal is improved metabolic flexibility and improved endurance exercise performance, then there’s some research to back up using fasted cardio.

If you just want to lose fat or get shredded, research has pretty definitively shown that training in a fasted state does not provide any measurable benefit vs. training in a fueled state.

At the end of the day, if you feel like something is working for you, and you’re seeing results and like the way you feel, then go for it!

*Note: This article contains affiliate links. Anything purchased comes at no additional cost to you.

Mike (Supastrong)
Mike (Supastrong)

Bioforce Certified Conditioning Coach and personal trainer. I’ve run boot camps and served as the wellness coordinator for a fortune 500 company. Currently a Federal Agent in San Diego, CA, and an Infantryman in the Army Reserve.

Cardio for Optimal Fat Burning, Weight Loss and Health

Cardio for Optimal Fat Burning, Weight Loss and Health

How can you properly do cardio for optimal weight loss, fat burning, fitness and health? My goal is to give you all the information you need, plus a cardio workout program at the end.

It is possibly the most overused word in the gym… “Cardio.”

  • The buff guy walking on the treadmill says he’s doing an hour of cardio.
  • The lady maxing out the speed on the elliptical says she’s doing cardio, right before she passes out from exhaustion.
  • The strange guy with the short shorts doing some form of a crossfit workout says it’s his cardio day.

Which one of them is actually doing cardio?

What is Cardio?

To answer the above question, we will need a definition of what cardio means. We’ll need to understand this so we can actually make sure we’re getting the benefits we think we are from the activity we’re doing.

Cardio is short for “cardiovascular.” I know you already knew that, but I’m going somewhere with this…

Training the cardiovascular system implies that we’re performing Aerobic exercise. Aerobic exercise is any activity from low to high intensity that relies primarily on the aerobic energy system; this means that the body is able to use oxygen to meet all of the demands of the activity.

Exercise Intensity Determines whether it’s aerobic or not.

As exercise intensity increases, the aerobic system can no longer supply all of the energy needed to continue. As a result, the anaerobic energy system will begin to dominate. Instead of oxygen, stored energy in the muscles will be used for energy, and will run out fairly quickly.

So, the buff guy on the treadmill gets a pass. The lady sprinting on the elliptical was probably outside of the aerobic zone. The short shorts guy doing Crossfit; well it really depends on the intensity and duration of his workout.


Let’s go ahead and get a definition so we can move on:

Cardio – Any activity, from low to high intensity, involving constant movement lasting at least 20 minutes, where the aerobic energy system is supplying the majority of the energy.

Cardio Can Serve Different Purposes

If I were your trainer, I would never tell you to go do “cardio.” I would tell you specifically:

  • What to do
  • How long to do it for
  • What heart rate range I want you in for the duration of the session
  • How it should feel to you (perceived exertion), on a scale from 1-10

This is because there is no best form of cardiovascular exercise. The best method of training depends entirely on your goals and your current abilities. The form of cardio you’re doing should match up with this.

Fat Burning and Weight Loss

fat burning cardio

Understanding how the body works can really open your eyes to what you’re doing in the gym.

Your body stores fat as a means to store energy for future use. Fat cells are basically balls of energy. It’s a survival mechanism. If food became scarce, that stored fat could keep you alive. Of course, food isn’t exactly scarce these days. We’re cursed with our own biological adaptations.

Our bodies burn fat most efficiently at rest and during low intensity activity. This is because the process of breaking down fat cells into energy is very efficient, but slow. Fat cannot be used to fuel more intense anaerobic activity. Thus, fat is burned most efficiently during lighter activity.

The traditional “fat burning” zone would look like this:

  • 50-70% of your max heart rate. (Max HR = 220 – Age)
  • A pace where you could carry a conversation, a level 3-5 on the perceived exertion scale.)
  • Use any cardio machine, fast walking/jogging, or a combination.
  • 30-60 minutes of low intensity exercise

For Optimal Fat Burning, You Need Higher Intensity Training

high intensity cardio

The “Fat Burning Zone” is great and all, but it’s only a piece to the puzzle. It is not the ultimate method for losing fat. Again, understanding our bodies can really give us insight into what we’re doing when we work out.

During higher intensity workouts, it’s true that we burn a smaller percentage of fat for energy. However, at higher intensities you’re also burning far more total calories. Less efficient doesn’t necessarily mean less total fat burned. Here’s an important fact to keep in mind:

The only place in the body where fat gets burned is in Muscle tissue

Training only at low intensities will never encourage your body to build or maintain muscle. More powerful muscles are fat burning machines. They take more energy to maintain. As a result, resistance training and higher intensity cardio can increase your resting metabolic rate.

Resting Metabolic Rate

Your resting metabolic rate is the amount of calories your body burns at rest. If you can burn more calories while you’re binge watching Netflix or shopping on amazon, you will inevitably lose more fat and become leaner.

Recovering from higher intensity workouts takes energy, too

Higher intensity workouts create an “after-burn” effect. Since the body requires more energy to recover from these sessions, additional calories will be used. Since you’re at rest while you recover, fat will be used to fuel this recovery. It’s a simple concept that adds value to incorporating some resistance training and higher intensity training to your workouts.

The 3 Cardio Zones

I don’t really like the traditional cardio “zones.” I like things to be simple, and there’s no need to complicate things unless you’re an elite athlete looking for very specific adaptations. I like breaking it down into 3 groups:

Low IntensityModerate IntensityHigh Intensity
Basic endurance
Good for beginners
Cardiac Output
Improve aerobic abilities
Build Endurance
Major Health Benefits
Training Zone
Aerobic Power
50-70% of Max HR70-80% Max HR80-90% Max HR
30-90 Minutes20-60 Minutes10-25 Minutes

How To Train in Each Zone

Here are some examples of how to train in each of the 3 zones. As you’ll see towards the end of this article, using a combination of these methods is what will get you optimal results for burning fat and losing weight.

Low Intensity

  • Use any cardio machine, brisk walking/jogging, or any light activity.
  • You should keep constant movement and be able to hold a conversation
  • You should feel like your level of exertion is a 3-5 out of 10.
  • Heart rate 50-70% of your max HR.
  • 30-60 minutes


  • Stimulates recovery in the body
  • Burns fat
  • Increases blood flow into joints and muscles

Moderate Intensity

  • Use any cardio machine, jogging or other activity
  • You should be able to talk, but not full conversation
  • Should feel hard but maintainable
  • Heart rate 70-80% of max HR
  • 20-60 minutes


  • Improved Cardiac Output: Heart pumps more blood per beat
  • Improved endurance
  • Increased size of left ventricle of the heart – (stronger heart)
  • Improved cardiovascular system
  • Studies show can reduce risk of dying from all causes

High Intensity

  • Running/Sprinting in intervals: (ex, 1 minute run, 1 minute walk).
  • Can use circuits with full body exercises done in intervals
  • Should feel difficult. Exertion 8-9 out of 10
  • HR 80-90% of max HR or greater.


  • Improved Aerobic power: Your body’s ability to use oxygen
  • Metabolic rate is higher for several hours after the workout
  • Can gain muscle
  • Can get a lot done in a short time

So What’s the Best Way to do Cardio?

As stated earlier, there is no “best method.” Each method has it’s own place in your plan of attack, and all three are necessary if you want optimal results in losing fat and improving your health and fitness.

For Best Results, Use Various Approaches.

The best results will come by reaping the benefits of all three forms of cardio:

Use High intensity training to stimulate aerobic power, build muscle and boost metabolic rate.

Use low intensity to promote recovery from harder workouts and to continue burning fat when you would otherwise be doing nothing.

Use Moderate intensity training most frequently to reap the massive benefits of improved aerobic fitness.

The Massive Benefits of Focusing on Moderate Intensity Training

Studies have shown that the higher a person’s level of aerobic fitness, the less chance that person has of dying from all causes. Read the quote below from the largest study on this topic every compiled:

“cardiorespiratory fitness was inversely associated with all-cause mortality without an observed upper limit of benefit.”

aerobic fitness and mortality

I’ve mentioned this before in previous articles because it is so important. Aerobic fitness and mortality are intimately related. Improving your aerobic fitness can help you not only feel better and live a better life, but also to live longer. Read the article for yourself here:

Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing

By performing different types of cardiovascular exercise, you can build your aerobic fitness from the ground up, while burning fat, losing weight and getting a more toned body in the process.

An example of how to split up your cardio workouts:

cardio for weight loss toned body

This is just an example. Depending on your current abilities, you can always do more or less. The important points to always keep in mind are:

  • Treat high intensity training with respect. More is not better. Studies show that 2 days per week, or 40 minutes per week, is optimal.
  • Use low intensity training to stimulate recovery and keep your body moving and burning calories and fat.
  • Focus on moderate intensity training to get the biggest overall benefits
fat burning workout cardio
Example of how to split up your workouts for optimal results.


I hope you enjoyed this article. If you think it’s important, feel free to share it. Cardio is often misunderstood, but is a critically important part of any workout program. Understanding how your body works and what you’re trying to accomplish can take you to new levels of fitness and health. As always, I hope this helps get you a little closer to that best version of you.

Mike (Supastrong)
Mike (Supastrong)

Bioforce Certified Conditioning Coach and personal trainer. I’ve run boot camps and served as the wellness coordinator for a fortune 500 company. Currently a Federal Agent in San Diego, CA, and an Infantryman in the Army Reserve.

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