Why You Should Stop Doing Fasted Cardio For Fat Loss

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Fasted Cardio Myth

Do you like cardio? Not many people do. If you do, then more power to you my friend. For everyone else out there, not so much. Add “fasted” to your cardio and it can get even worse! We’ve all been told that fasted cardio is the most effective way to lose fat. Imagine if doing long, slow, time consuming stead-state cardio was not necessary for fat loss? Especially not necessary to be in a “fasted” state while doing it!

It’s not!

I’m going to break-down what fasted cardio is, why the conventional wisdom says that it works, and what the science says about it. Then I want to tell you about my method for High Intensity Interval Training, and why it is superior for overall fat loss. No fasting required!

Fasted Cardio Study

I’ve long been a subscriber to the logic of waking up and heading to the treadmill before eating, so I can get my cardio in while I’m in a fasted state.

The idea behind this is that in the absence of additional carbohydrates in the body, for use as energy for cardio, the body would instead be forced to use fat stores for its energy source.

As a result, I’m losing weight (fat loss) and patting myself on the back for tricking my body into doing what I want.

I’ve used this fasted cardio method for years. Enough that I decided to write a post about the benefits and why I use fasted cardio myself for fat loss. I started searching for some studies that I could use for an expert opinion on the topic.

I landed on a study from 2014, conducted by the US National Library of Medicine. Their experiment consisted of two groups of women–10 to a group.

As I continued to read, I was surprised to see this:

Twenty healthy young female volunteers were randomly assigned to 1 of 2 experimental groups: a fasted training (FASTED) group that performed exercise after an overnight fast (n = 10) or a post-prandial training (FED) group that consumed a meal prior to exercise (n = 10). Training consisted of 1 hour of steady-state aerobic exercise performed 3 days per week.

Subjects were provided with customized dietary plans designed to induce a caloric deficit. Nutritional counseling was provided throughout the study period to help ensure dietary adherence and self-reported food intake was monitored on a regular basis.

A meal replacement shake was provided either immediately prior to exercise for the FED group or immediately following exercise for the FASTED group,(emphasis mine) with this nutritional provision carried out under the supervision of a research assistant.

Both groups showed a significant loss of weight (P = 0.0005) and fat mass (P = 0.02) from baseline, but no significant between-group differences were noted in any outcome measure. These findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless whether or not an individual is fasted prior to training. (emphasis mine)

US National Library of Medicine


So that pretty much changed everything for what I thought to be true.

This study shows that there was very little difference with regard to fat loss if you trained in a fasted or fed state.

In conclusion, our findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless whether or not an individual is fasted prior to training.

Hence, those seeking to lose body fat conceivably can choose to train either before or after eating based on preference.

US National Library of Medicine
The study does point out however, that based on the small sample size and short study duration, they can’t rule out that fasted or fed cardio might have an advantage over one or the other in the long term, with respect to fat loss.

What is Fasted Cardio?


Burning Fat in the Absence of Carbs

This is the main reason behind why people do fasted cardio.

The myfitnesspal blog explained it like this:

“A true fasted state starts at about 8–12 hours after your last meal,” says registered dietitian Allison Childress, PhD, a certified specialist in sports dietetics and assistant professor at Texas Tech University.

For some, doing fasted cardio happens in the early hours of the day, simply because they don’t have time to eat breakfast pre-sweat. According to science, there can be some benefits of getting after it sans fuel.

People can burn up to 20% more body fat by exercising in the morning on an empty stomach, according to one study published in the British Journal of Nutrition. (emphasis mine) Another University of Scranton study revealed it may lead to reduced calorie consumption in the 24 hours that follow the fasted workout.

“The idea is that exercising in a fasted state burns stored energy (fat and glycogen) versus energy you have just consumed,” says Childress, who notes that this strategy works differently for everyone. While you may see your BFF lose fat from fasted cardio, you may not see any fat loss yourself.

“What is Fasted Cardio and Does it Work?” by Emily Abbate, MyfitnessPal Blog
OK. So basically, the sum of this introductory paragraph is that it may or may not work for you. I decided to go check out the two studies that were referenced here for a competing point of view to the study I read in the US National Library of Medicine.

The first study, conducted by Northumbria University concludes that those who had exercised in the morning, presumably in a fasted state, did not experience increased appetite, nor did they consume more food later in the day as a result of exercising while in a fasted state.

Which, is not really the information I was looking for.

The myfitnesspal blog article used the figure from the British Journal of Nutrition that people can burn up to 20% more body fat by exercising in the morning on an empty stomach. However, how did they arrive at this number?

The rest of the article says this:

Researchers, led by Dr Emma Stevenson and PhD student Javier Gonzalez, asked twelve physically active male participants to perform a bout of treadmill exercise at 10am, either after they had eaten breakfast or in a fasted state having not eaten since the evening before.

Following the exercise all participants were given a chocolate milkshake recovery drink. Later in the day, participants were provided with a pasta lunch which they were asked to consume until they felt ‘comfortably full’. Their lunchtime consumption of energy and fat was assessed and calculated, taking into account the amount of energy and fat burned during the morning period.

The researchers discovered that those who had exercised in the morning did not consume additional calories or experience increased appetite during the day to compensate for their earlier activity.

They also found that those who had exercised in a fasted state burned almost 20% more fat compared to those who had consumed breakfast before their workout. This means that performing exercise on an empty stomach provides the most desirable outcome for fat loss.

“Lose Fat Faster Before Breakfast”
The part that bothers me is that maybe the group that fasted burned 20% more fat compared to those who had consumed breakfast before their workout because–from what I could read in the study—they had consumed an extra meal that day (breakfast), as compared to the fasted group.

Is the fact that they burned 20% more fat due to the fact they ultimately consumed less calories that day?

I don’t know, the source article doesn’t go into depth about how this conclusion was reached.

Maybe the real conclusion should be that those who consume less calories will burn more fat. Regardless of when exercise is performed.

The University of Scranton study that was also cited confirmed that exercising while fasted will not lead to additional consumption of calories later in the day.

Cool. But not exactly what I was looking for.

Again, the study either gave their participants breakfast before exercise or did not, after which both groups ate the same amount of calories at lunch and then a bag of food to take home.

Still, the fasted group is taking in less calories than the fed group.

To me, the real conclusion is to decrease overall calorie intake, regardless of when you exercise.

I think this study would have been more effective had the fasted participants been fed directly after the morning exercise.

One interesting conclusion of this study, though, says this:

What we did not expect to find was that when participants fasted they also consumed less energy during their evening meals and snacks compared to the days when they ate breakfast. The reduced 24-hour energy intake on fasting days was not only due to the fact that breakfast was skipped but also due to a decreased energy intake at night. This finding suggests that fasting prior to exercise may suppress energy intake over an extended period of time. (emphasis mine)

I again wonder if this is a result of the fasting itself than a combination of fasted cardio.


I thought about my own experience with fasted cardio, and I started to think of ways to accelerate fat loss, since apparently training while in a fasted state would not accelerate fast loss like I thought it would.

One thing I’ve noticed, is that when I’m performing fasted cardio, my performance suffers—big time. I feel like crap, every step gets harder and in general I’m fatiguing much quicker than if I were to eat 30-45 mins before I started cardio.

But wouldn’t that defeat the purpose of fasted cardio? Wouldn’t my body be using all this energy from the food I just consumed to power my workout as opposed to the fat stores my body has put away for what I can only assume is the coming apocalypse.

Maybe there is a different way?

Interested in losing weight this year? How about gaining muscle? I’ve got you covered on both here.

Fasted Cardio HIIT


I started searching for alternatives to steady state cardio on the treadmill for 30, 45 and 60 mins at a time. I came across High Intensity Interval Training.

What if we are to take the concept of fasted steady-state cardio and use HIIT training instead, when a light meal was consumed prior to the HIIT session?

Pretty cool.

After all, the study stated specifically that the subjects were using a steady-state cardio for their training. What if this were changed to a high intensity interval training?

The concept here is that I can go almost all out for 30 seconds to 1 minute and then rest for a set interval and repeat. This way I could possibly burn the same number of calories in a shorter period of time.

I like that!

What if I were to eat a small amount of food, 30-45 minutes before starting my workout and instead of doing fasted, steady state cardio, I did HIIT training? Would this be more effective for over-all fat loss?

I set out to see if I could find the answer to my question.

I decided to write down my hypothesis in a logical way, and here is what I came up with:

My Hypothesis

Eating a small amount of food in the form of a fruit or other food low on the glycemic index can help to increase performance and intensity, stave off muscle fatigue and maximize the afterburn effect. Especially when paired with HIIT. This is more beneficial than performing a steady state cardio exercise in a fasted state.

Pretty sweet.

High intensity interval training or (HIIT) is pretty self-explanatory, and to be honest, doesn’t sound like something I really want to do first thing in the morning. But I want to push outside the comfort zone here. explains how it works, in their blog post on high intensity interval training.

It says that high intensity intervals of training should be done at 80%-95% of your maximal aerobic capacity. So nearly as hard as you can go. They say intervals should range from 30 seconds to 3 mins with the rest intervals to be equal to or longer than the speed intervals.

Fasted Cardio Workouts

The sample workout given in this article shows this:

  • 5-minute warm-up
  • Followed by a 1-minute speed interval
  • 2-minute rest interval.
  • Then finished with a 5-minute cool down.
  • 22 minutes of total time and 4 minutes of total speed intervals.

I’m sure example workouts can be found anywhere on the internet or YouTube. I did a quick YouTube search for HIIT training and found a video I liked below.


Intensity level of exercise increases total fat loss

My belief is that the increased intensity level of HIIT training will lead to more fat loss than the steady state cardio as a base line.

The International Journal of Obesity published an article studying this and found this:

Both steady state exercise and HIIT improved cardiovascular fitness, but that HIIT training induced a “significant reduction in total body mass (TBM), fat mass (FM), trunk fat and fasting plasma insulin levels. There was significant fat loss (P<0.05) in legs compared to arms in the HIIE (HIIT) group only.”

Glycemic Index and foods with low glycemic index

Why talk about the Glycemic index and foods with a low glycemic index? The glycemic index starts with carbohydrates. The glycemic index is ranking carbs from low to high.

The idea is that not all carbs are created equal. The general line of thought is that carbs with a lower GI level will be digested and absorbed more slowly into the blood stream.

In other words, it is a measure of how quickly food you eat causes your blood sugar level to rise. The scale rages from 0 to 100. 0 is good and 100 is bad. Foods that rank high on the glycemic index are normally high in processed carbohydrates and sugars. They in turn are quickly absorbed into the blood stream, causing a rapid increase in blood glucose levels.

Burning glycemic stores and not replenishing them from a carb source can lead to early muscle fatigue.

I want to forego having to perform my morning HIIT workout on a completely empty stomach, but if I eat a donut to get some food into my body for that extra energy required to complete a hard workout, it would not be very effective.

Where do you think a donut might end up on the glycemic index? I checked, and it’s not great. A donut comes in at a 76 out of a 100 on the scale.

Not good.

The point here is to eat a small amount of a slower digesting carb source that is low on the glycemic index. This will give me the energy I need to not “bonk” during my HIIT session, perform at that 80%-95% max range and maximize the afterburn affect to torch the fat.

Low Glycemic Foods For Breakfast


Afterburn Effect of Exercise

What happens to our body after we’re done exercising? Do we burn calories (energy expenditure) while we are exercising, only for the calorie burning to end as soon as your work out does?


You will actually continue to burn calories even after your work-out is over. This is called the “afterburn effect of exercise”. This will take place generally when you have finished a higher intensity workout.

What actually happens to our body when we have completed a high intensity workout?

When you start that HIIT workout and call on your muscles to contract and move at a high level, your body kicks into action. Glycogen and adenosine triphosohate—a compound molecule in your tissue—is called to generate the energy required to power the muscle through the movement.

This ATP, as it’s called, runs out however, and your body will need to take in more oxygen in order to create more ATP. In order to get the oxygen to the muscle, your heart kicks in to gear to deliver more blood to the muscle groups, and thus, more oxygen to those muscles in order to create the ATP for energy. Without sufficient oxygen delivered to the muscles, lactic acid will form in its place. This is what creates the burning sensation in your muscles.

As your body gets more efficient at delivering oxygen to the muscles, the easier the workouts will get. This is because the lactic acid will not build up and fatigue the muscles.

A post featured on the Huffington Post, gives a detailed break down on what happens to the body when you exercise.



The reason for this afterburn effect, is that when you are performing a very high intensity exercise, your body can develop an oxygen debt, as it is attempting to deliver to your muscles during exercise. Your body must re-pay this debt in order to allow your body and muscles to recover.

If you are finished with your HIIT workout and the oxygen debt remains, your body must still utilize stored energy to bring it back into a rested state. This is burning calories! A steady state workout will not have a similar effect.

We can think of the afterburn effect like starting a camp fire (intense exercise). You go to bed and leave that fire burning. The fire doesn’t go out immediately. It burns through the night. When you wake up the next morning the coals are still glowing red. This is similar for your body and the afterburn effect.

The Campfire HIIT Method

I’ve taken my hypothesis from earlier and put it into action. I’m calling this the Campfire HIIT Method. I’ll be eating small portions of food, mainly for breakfast, that are low on the glycemic index.

This will give me the energy my body needs to perform the HIIT session at a high level, with less fatigue. When the HIIT session is completed, my body will need to replenish and recover from this workout. This will result in the afterburn effect of exercise and allow my body to continue burning fat like red hot coals long after I’ve ended my workout.

I believe that using this method is far superior to the practice of fasted, steady-state cardio for fat loss.


What Do You Think?

What are your thoughts on HIIT training, fasted cardio and The Campfire HIIT Method? Don’t agree with the concepts presented? Hit me with your opinion! Have you tried the method and love it? Let me know! I’d love to hear from you so drop a comment and e-mail. For more information, remember to sign up for the Guardian-Elite Fitness Newsletter.