What Is Fasted Cardio?
Fasted cardio is when you do a moderate to intense workout on an empty stomach.
An empty stomach means that you have not eaten for 8 to 12 hours and no pre-workout meal either.
Does Fasted Cardio Work to Burn More Fat?
Fasted cardio study results are mixed.
On one hand, the British Journal of Nutrition reports that fasted workouts can burn up to 20 percent more fat than non-fasted. ¹
The theory is that during a fast, such as sleeping overnight, your body uses the calories in your skeletal muscles to perform necessary functions.
By the time you wake up, the carbohydrates that were stored in your muscle cells in the form of glycogen have been used up.
This reduction of carbohydrate stores in your muscles is known as glycogen depletion.
Since your muscles no longer have glycogen stores to draw on for energy, your body needs to get energy from your fat cells.
Also, studies by the National Institute of Health show that lower blood sugar results in lower insulin levels which allows your body to draw energy from your fat stores as well. ²
Forcing your body’s energy system to turn to your fat for fuel is one primary benefit of fasted cardio, and explains why you can burn more body fat in a fasted state.
Why You Should Do Fasted Cardio
Effect of Fasted Exercise on Body Composition
However, research published in the Journal of Functional Morphology and Kinesiology shows that fasted exercise is no better than fed-exercise in terms of improving weight loss or body composition.
The conclusion of this study is that caloric deficit is the most important variable for weight loss and fat loss, and not exercising in a fasted state. ³
Benefits of Fasted Cardio
If accelerated fat loss and weight loss is a fasted cardio myth as the previous study suggests, why should you do fasted cardio?
Here are some surprising benefits of fasted cardio:
#1. Set the mood of your day
When you train first thing in the morning, the last thing you want to do is scarf down a blueberry muffin.
Morning cardio will wake up your entire body, and energize you for the rest of the day.
Because you make your fitness a priority, you are more likely to eat healthy real food, avoid processed junk, and too much snacking.
A simple low impact 30-minute walk will prime your entire body without fear of muscle loss.
#2. Create the caloric deficit you need for weight loss and fat loss
For example, doing fasted cardio in the morning will push your breakfast an hour or two later into the day.
As a result, you will find yourself snacking less during the day, which in turn keeps your calories under control.
Not that you need to count calories!
But the main point is that fasted cardio results in having less time to eat during the day.
Also, my top fasted cardio recommendation, a 30-minute brisk morning walk, is easy to do and will on average burn 200 calories.
#3. Make your workout a priority
It is more likely to miss training when you leave your workout until later in the day.
Things come up, meetings, appointments, dates, functions, it is impossible to anticipate what will happen later in the day.
Therefore, if for example, you get in a fasted workout first thing in the morning, at least you know you attended to your cardiorespiratory fitness first.
And there is little more important than protecting the health of your heart.
#4. Removes the problem of sluggishness after a meal.
You might not be able to do a proper workout after having a meal.
In that case, fasted exercise makes a lot of sense.
Even when you know you will be free for a workout later in the day.
#5. An excellent option for people who do not like to eat in the morning
If you do not like to eat early in the morning, fasted exercise is a good option for getting your training in at the start of the day.
Does Fasted Cardio Burn More Fat or is it a Myth?
How long should you do fasted cardio for?
You should keep your fasted cardio to 30-minutes and no more than an hour.
This time restriction is because your energy levels and subsequently, your exercise performance, might not be as high in a fasted state, as it is in a fed state when you have replenished the glycogen in your muscles so they will have immediate access to energy.
If you are in the middle of a fasted workout and suddenly feel a sense of nausea or complete exhaustion, you could be entering the state of ‘bonking’.
Going longer than 30 minutes to an hour could bring you into bonking territory.
Another downside to fasted cardio is that studies show that fasted exercise can result in muscle loss, the opposite of what you want to accomplish with training, which is to build muscle.
It is for this potential muscle loss that you should not engage in fasted HIIT cardio (High-Intensity Interval Training).
Also, strength training as well is not advisable in a fasted state according to Registered Dietitian Jim White, R.D.N, an ACSM exercise physiologist.
Killer 10 Minute Fat Burning Workout from Funk Roberts
Fasted Cardio – Final Thoughts
To sum up, the best fasted cardio workout is the one that you enjoy, that will not cannibalize muscle tissue, and that you will stick with consistently.
Whether you like
- jumping jacks,
- stair climbing, or
the choice is yours.
While you can even do fasted cardio workouts with squats, deadlift, and bench press by shortening the rest periods between each set from the typical 3 to 5 minute rest period down to 30 seconds, this is not advisable.
The reason is that you will not have enough energy for strength training in a fasted state and you will lose muscle tissue as mentioned above.
Based on all the current data, a brisk walk in the morning for 30 minutes is the best fasted cardio solution.
Cardio is important for overall conditioning and cardiorespiratory fitness, one of the 5 essential components of physical fitness.
But if you want to get lean, build muscle, and dramatically improve your physique, you need resistance training.
The next step of your fitness journey is to understand why weight training is so critical to your goal of fat loss and muscle growth.
Therefore, find out Why Deadlifts Are So Great and learn about the 7 Greatest Deadlift Muscles Worked That Can Change Your Life.
Last but not least, please check out my new weight loss plan ebook:
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¹ Breakfast and energy balance in physically active males – British Journal of Nutrition
² Lipolytic suppression following carbohydrate ingestion limits fatty acids oxidation – National Institutes of Health
³ Effect of Overnight Fasted Exercise on Weight Loss and Body Composition – Journal of Morphology and Kinesiology