Does Fasted Cardio Burn More Fat?
I remember the first time I did fasted cardio.
- “Do I really want that Rambo III physique?”
- “If the clocks went back an hour last night, does that mean I need to train two hours?”
- “Baloo the bear from Jungle Book always looks so happy. Bet he never does this.”
Each of the above were genuine thoughts running through my head as I woke up at F**k O’ Clock in the morning, ready to pound the treadmill and slowly rob myself of the will to live…
… and it was all in the name of fat loss!
Because for many years, muscle building magazines have told us that we must do this in order to look great naked. Fasted cardio will help you burn more fat, and rid yourself of those last layers of stubborn blubber preventing you from seeing your abs.
But is it true?
Today I’ll put this popular bodybuilding belief to the test, as I use the latest fitness science to answer the all-important question; does fasted cardio burn more fat?
Fasted Cardio Confusion
Before I explain how fasted cardio works, I want to debunk the most popular myth surrounding it.
The fitness industry is rife will poor advice, and the majority of people feel lost because the majority of so-called experts are giving bulls**t advice.
One such piece of advice pertaining to fasted cardio is the belief that eating before training means you’re only burning the food you just ate.
It’s not true.
But it’s a myth which runs right through the fitness world, and I want to kill it today.
Let’s take a quick look at the Netflix documentary The Perfect Physique.
In this show, a group of fitness models sit around a table discussing their training routine. Given the large potential audience of the program, they had a platform to do great things here. Unfortunately, it’s a 90 minute Instagram caption (“Never stop never stopping giving up”) literally packed with scientific flaws.
And a few of them concerned fasted cardio…
Example; when one lone model insists he prefers to do cardio after a light meal, the group gasp in shock and awe…
“Really bro? Why not fasted cardio? Aren’t you worried that by eating first that’s all you’re burning off in your workout?”
That’s not how any of this works.
(Otherwise, how would people who train in the evening burn any fat at all?!)
But the suck gets harder…
Later on these guys insist you should eat every 2-3 hours to prevent muscle loss – ignoring the fact that they deliberately put themselves into a fasted state for 8 hours every night before hitting the gym!
At this point, I’m fixing to roundhouse kick my TV…
When questioned, they say things like “No, because I take BCAAs to prevent muscle breakdown.” As I revealed in this article, that means they’re not doing fasted cardio at all.
That’s it. I’m done. I can take no more.
It’s a prime example of why you shouldn’t listen to every guy at the gym who happens to be in shape.
But it’s also a good example of how easily myths can turn into popular beliefs.
So in the next section I’m going to show you how fasted cardio actually works, and how it burns fat, to put you one step ahead of the game.
How Does Fasted Cardio Work?
Let me start out by making it very clear that fasted cardio does indeed work.
You will burn calories (of course), and you will lose fat as a result of said calorie burn.
I’ve done fasted cardio before, and so have many of my personal training clients.
Alongside the benefits above, it can make you feel lean AF and there’s definitely something satisfying about getting into a calorie deficit as soon as the day begins.
Russ 1… Calories 0….
There’s a two-fold theory behind why fasted cardio is a more effective way to burn fat:
- Our cortisol levels are higher in the morning. Cortisol promotes the metabolism of fat for energy, therefore training in this environment causes us to burn more fat.
- We’ll have less carbohydrates in our system, forcing our body to use fat as its primary fuel.
Both theories make sense.
Throw in the fact that celebrities like Jennifer Lopez have started incorporating it into their routine, and it seems like a no-brainer, right?
But don’t be so quick here.
Barely any of my clients (nor myself) use this technique anymore.
Times have changed, and superior methods have been discovered.
Today I’m going to introduce you to something I call the Full Tank method, and explain why it has replaced fasted cardio as the “go to” fat loss method of my clients…
Fasted Cardio Vs Fed Cardio
The scientific theory behind fasted cardio is solid.
With no carbs in your system, you’ll burn fat instead.
But in the ever-changing world of sports science, you have to keep your ear to the ground for new developments. The first time I questioned fasted cardio was during my initial personal training certification over 15 years ago.
My lecturer brought up the very valid point that, “High intensity cardio would primarily burn carbs for fuel, and low intensity cardio would burn fat. A lack of carbs will force you to train at a low intensity, and if you’re performing low intensity cardio you’ll burn fat as the primary fuel anyway.”
Surely, if I wanted to, I could eat before training then go perform low intensity cardio and burn the same amount of fat anyway?
And it stacked up, too.
Because since then, modern research has shown us that fasted cardio isn’t the holy grail we once believed it to be.
A study published in the Journal of Applied Physiology had researchers directly compare the effects of pre workout carbohydrates against fasted cardio. They confirmed that training in a fasted state had statistically insignificant results on overall fat loss achieved. (2)
(Take that, Netflix documentary…)
And in 2011, a great meta-analysis published in the Strength and Conditioning Journal by Dr. Brad Schoenfeld confirmed that fasted cardio is no better at creating fat loss than training in a fed state. (1)
As explained in this article, what matters more is energy balance.
If one guy ate 2000 calories and did fasted cardio, and you ate carbohydrates before training but still ate 2000 calories overall, you can expect the same results.
By exercising in a fasted state we will burn more fat during exercise, but the body counter-balances this by burning more glucose during the rest of the day. Likewise, you will burn more glucose during exercise if you eat before training, but you’ll burn more fat during the remainder of the day.
A 2019 study published in the Journal of Nutrition claimed to have found proof that fasted cardio burns more fat, but when we delve deeper into the results we can see that it falls in line with the previous research…
During this trial, one group of trainees performed early morning fasted cardio while another group performed fed cardio.
Sure enough, the fasted cardio group had achieved a greater calorie deficit over the course of the day. (7)
But it wasn’t because of the fasted cardio…
The extra calorie deficit was completely explained by the fact that the fasted group skipped breakfast before exercise and didn’t replace those calories, meaning they actually ate less food, therefore creating the calorie deficit.
The difference in energy expenditure during exercise, however, was non-existent.
The American Council on Exercise brings up some very valid points in this article:
- Exercise in a fasted state could burn more calories from fat, but it also could cause the body to burn protein for fuel, which would reduce the amount that can be used to help repair and build muscle tissue. Gluconeogenesis is the process of converting proteins to glucose for energy. In short, if carbohydrates (glycogen in muscle and liver, glucose in the blood stream) are not immediately available for energy, the body can convert proteins for fuel, which leaves fewer proteins available to rebuild muscle post-exercise.
- The body has plenty of free fatty acids (FFAs) available for exercise. The FFAs that are not immediately converted to energy to fuel muscle activity can be redeposited in adipose tissue in the abdominal region. In other words, they will end up as belly fat. Exercising when cortisol levels are higher could lead to more FFAs circulating in the blood than can be used. So, rather than depleting levels of fat, exercise first thing in the morning could actually shift body fat to the abdominal region.
- If the goal is weight loss by metabolizing as much fat as possible, it is more important to consider energy expenditure over a 24-hour period and not just at one point during the day. Monitoring energy intake and expenditure throughout the day and identifying how to reduce excessive intake and increase opportunities to move can play a more significant role in long-term weight loss than trying to burn more fat by exercising first thing in the morning.
The Full Tank Method
We now know that eating carbs before low intensity cardio will not prevent you from burning fat.
But what about protein?
Here’s where things get interesting…
New research suggests that consuming protein before training will yield slightly superior results versus fasted cardio, both in terms of performance and calorie burn.
So if fasted cardio leaves you feeling emptier than a politician’s promises, this is a good alternative.
I call this the Full Tank method.
Simply grab a protein shake about an hour before training (not too close, or you’ll feel bloated), then do your cardio workout.
It’s that simple.
By hitting the gym with a ‘full tank’, you will be able to work harder during training, you will increase your calorie burn thanks to protein’s thermogenic effects, and you’ll stave off hunger until you’ve finished training.
But don’t just take my word for it…
A 2010 study published in Medicine And Science In Sports & Exercise was the first official paper to reveal the benefits of consuming pre workout protein rather than training on an empty stomach.
Protein helped to boost metabolic rate and also increase total calorie burn.
Interestingly, the researchers also found that pre workout protein achieved better results than pre workout carbohydrates, meaning consuming protein was superior to eating other foods or no food at all! (3)
One year later, a study published in the International Journal of Sport Nutrition and Exercise Metabolism looked even further into this…
This time, Italian researchers set out to specifically measure the fat loss benefits of training in a fasted or fed state.
To do this, they compared two groups of trainees each doing separate 36 minute moderate intensity cardio workouts, the only difference being group A performed their cardio on an empty stomach and group B had protein beforehand.
Once again, the protein group burned more calories (and more fat) than the other group. (4)
Incidentally, they were still burning more calories a full 24 hours after the workout ended!
The authors had this to say:
“When moderate intensity exercise is done to lose body fat, fasting before exercise does not enhance lipid utilization.
Rather, physical activity after a light meal is advisable.”– Dr. Antonio Paoli, Department of Biomedical Sciences, University of Padua, Italy.
Before I wrap up, I must talk about training intensity.
If you’re a regular reader, we know that I’m a huge fan of HIIT for stripping body fat.
But HIIT presents its own set of problems regarding fasted cardio, because high intensity interval training workouts (“high intensity” being the operative words) are designed to be performed in a fed state. (5)
In the absence of fuel for HIIT (specifically, carbohydrates), it is far less productive and the fat burn after the workout will be significantly lower. (6)
Tackle any of the HIIT workouts from my website in a fasted state and you can expect to crawl over the finish line feeling like an extra from Z-Nation.
(Everyone knows a Z-Nation reference is cooler than a Walking Dead reference, right?)
But There Are Exceptions To The Fasted Cardio Rules…
Yes, even though research shows us that protein before cardio will slightly increase results, it’s not for everyone.
There are two groups I’m referring to here:
- Some people just prefer doing fasted cardio. It works, you’ll still burn fat, and that’s fine. You do you.
- People who use intermittent fasting.
That second group often gets overlooked, but not in this post!
I mentioned at the top of the content that barely any of my clients performed early morning fasted cardio anymore.
Why not none?
Well, intermittent fasting is a dieting technique which sometimes forces the individual to remain in a fasted state during their cardio session. It comes with its own set of fat loss benefits, but unless you can pick the exact training times you want in lieu of your working hours, difficult decisions need to be made along the way.
(i.e. you might be forced to fit your workout in during your fasting period.)
Do we live in a perfect world where everything is all sunshine and rainbows?
No, we don’t.
We live in a crazy f**ked up world where Gwyneth Paltrow makes a living selling health and fitness products despite owning no health and fitness qualifications.
So you must choose one.
On the other hand, if you’re simply looking for a way to power through your cardio workout more efficiently, to slightly increase calorie burn, and also stave off hunger during training, give my Full Tank method a try and let me know how you do.
If you’ve enjoyed this write-up: “Does fasted cardio burn more fat?”, get yourself on my email list below so you can get more training tips, straight outta my gym!
Yours in training,
- Schoenfeld, B. Does Cardio After an Overnight Fast Maximize Fat Loss? Str Cond J. (2011)
- Febbraio, M. A., et al. Effects of carbohydrate ingestion before and during exercise on glucose kinetics and performance. (2000)
- Hackney, K.J., et al. Timing Protein Intake Increases Energy Expenditure 24 H After Resistance Training. Med Sci Sports Exerc. (2010)
- Paoli, A., et al. Exercising Fasting Or Fed To Enhance Fat Loss? Influence Of Food Intake On Respiratory ratio And Excess Post Exercise Oxygen Consumption After A Bout Of Endurance Training. Int J Sport Nutr Exerc Metab. (2011)
- Wright, D. A., et al. Carbohydrate feedings before, during, or in combination improve cycling endurance performance. J Appl Physiol. (1991)
- Schabort, E. J., et al. The effect of a preexercise meal on time to fatigue during prolonged cycling exercise. Med Sci Sports Exerc. (1999)
- Edinburgh, R. M., et al. Skipping Breakfast Before Exercise Creates a More Negative 24-hour Energy Balance: A Randomized Controlled Trial in Healthy Physically Active Young Men. The Journal of Nutrition. (2019)