Fasted Cardio: More Than Just A Fat Loss Tool

Fasted Cardio: More Than Just A Fat Loss Tool

Why every high performer should consider incorporating fasted cardio into their routine.

Ivan Gavranic Ivan Gavranic · 04 Oct 2021

Mindset Intermediate
19 Mins

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Is Fasted Cardio Better For Fat Loss? 


For many years, one of the hallmark strategies for getting into shape was performing cardiovascular work in the fasted state, usually first thing in the morning. If you weren’t doing your cardio fasted, you were missing out on a huge fat burning window. What better time to burn fat when you haven’t consumed anything for 12-16 hours right? Your body HAS to tap into body fat stores for energy right?

Well, mechanistically that is all correct. Fat oxidation rates are much higher when you are fasting, especially when performing cardiovascular work and/or resistance training. Plenty of research has shown this but unfortunately, just because you’re burning more fat during your workout, doesn’t necessarily translate to better fat loss overall.

If you are eating more than you’re expending, you can be “a fat burning machine” all you want during your fasted cardio session, but you won’t be getting any leaner. For fat loss, whether or not you do your cardiovascular work fasted or fed, the majority of research has shown no impact in calorie matched conditions.

Interestingly, there was one very well designed study we were able to find that compared cardio done either before breakfast, after lunch or after dinner. The protocol consisted of each subject performing 60 minutes of aerobic activity at 50% of VO2 max (a very sustainable pace, nothing crazy) and most importantly, everything was done in a metabolic chamber meaning the scientists had 100% control over their energy intake and could measure their energy expenditure with the most accurate technology we have available.

Each subject (10 non obese, healthy young males) performed the exercise protocol at all different times across a two month period. Between sessions, they were asked to remain weight stable and each individual appeared to have accomplished this. The scientists made sure each subject was weight stable during each experiment, meaning they would match their energy intake with their energy expenditure.

The results showed that energy expenditure during each session was virtually the same across the board with higher rates of fat oxidation with the before breakfast intervention. As mentioned above, this isn’t anything new but what makes this study more interesting is that over the course of 24 hours, there was a significant increase in fat oxidation rates (~300 calories more) with the before breakfast intervention that wasn’t seen in the other interventions. The key understanding here is that yes, overall energy expenditure was virtually the same across the day but a higher percentage of that energy was coming from fat oxidation in the fasted cardio group.

Long story short, training in the fasted state depletes glycogen stores at a faster rate which then sends downstream signals to “turn on” fat oxidation creating a larger energy gap. Once we start eating, fat oxidation can still remain relatively high as our body tries to restore that lost glycogen.

The authors were very clear that this finding doesn’t necessarily mean it translates to better overall fat loss (which we 100% agree with) but nonetheless, it does provide a very interesting framework or potential benefit to incorporating fasted cardio especially as one gets closer to their checkpoint.

If we take those same numbers from above, 300 calories extra coming from fat oxidation could translate to an extra pound of fat (that contains ~3500 calories) lost in two weeks by just changing the timing of your cardio sessions.

Granted, this would mean doing an hour of cardio every morning but if you’re really pushing the envelope from an activity standpoint, you could be getting more “juice from the squeeze” by incorporating fasted cardio into your protocol.

For most individuals though, we would rather you focus on your nutrition, resistance training and general activity before even trying to leverage cardio to enhance your fat loss efforts. Cardiovascular work in general is a “nice to have” vs a “must have” when it comes to your body composition (read more here).

At this point, you may be asking yourself “If I can get the same results without it, why the heck should I even consider it?”

Don’t worry, for a high performer like yourself there are a myriad of benefits that go beyond fat loss in and of itself.

Don’t Throw The Baby Out With The Bathwater


Just because fasted cardio isn’t any better for fat loss from a mechanistic perspective, we shouldn’t be too hasty with our decision to completely dismiss it. The factors that go into fat loss are far more convoluted than just ‘eat less, move more’ and if we can find any way to make adherence to a plan easier, we are going to have far more success.

For many busy high performers, one of the very few times in the day that they have for themselves are mornings, meaning you want to get the most “bang for your buck” during these hours. Once the working day starts, many things can be thrown at you that can make it more difficult to get to your afternoon/evening session. Also, if you are making big decisions, leading a team or dealing with many people throughout the day, the accumulated fatigue can really add up.That means even if you did make it to the gym eventually, you may struggle to push yourself as your “cognitive resources” have been depleted. Research shows that mental fatigue can impact your physical performance by increasing your perceived level of effort for a certain task, meaning for something that is usually a 5/10 from a difficulty standpoint can now become a 7 or 8/10.

If you know you have a cemented block of time in the morning for physical activity, nothing can really get in the way of your training, especially if you wake up before anyone else in your family. Long term RNT member Akash Desai wakes up extremely early each morning to get his training in as he knows once the day starts, he will struggle to find the time. This has played a massive role in allowing him to stay in shape for years now after struggling for decades prior to joining RNT.
Akash Desai

Circadian Entrainment


We have written about circadian rhythms here and just how important they are for long term health outcomes. In fact, this article from 2019 went as far as to say that the term Metabolic Syndrome should be changed to “Circadian Syndrome” due to all the health ailments that can arise from misaligned rhythms.

Here is a direct quote from the same article.

“Abnormal circadian rhythms have been associated with obesity, Type 2 Diabetes Mellitus, Cardiovascular Disease and hypertension, all components of the Metabolic Syndrome. Shift workers or people who sleep poorly are more likely to develop obesity and T2DM due to circadian clock disruption.”

So what does this have to do with fasted cardio? One of the main components that helps regulate and “set” your internal body clock is exercise. This is partly why your body can get accustomed to any time you train if you do it for long enough. More importantly though, the hormonal milieu that occurs during the early hours of the day also coincides with what we want during exercise which is higher levels of cortisol, adrenaline and alertness.

This makes a lot of sense from an evolutionary perspective too as for most of our time on earth, we had to go “searching” for our first meal after we woke up or run away from potential threats.

Our circadian clocks work due to regularity and anticipation of certain events so we can use this to our advantage by cementing that early morning time for “activity” meaning you will naturally start to wake up earlier, go to bed earlier and have more energy first thing in the morning. 

Not only can this work wonders for your fat loss efforts (more consistency and adherence to early morning sessions) but you might be setting yourself up for better long term health outcomes too. If you start waking up each and every morning with energy, you are far more likely to engage in physical activity.

Mood & Productivity Benefits From Fasted Cardio


If you want to perform at your highest capacity, how you feel from day to day will have a huge impact on your overall productivity and longevity in whatever endeavour you’re pursuing. There are always going to be disappointments, people letting you down, projects not turning out the way you predicted and many other factors that come with high performance.

Being able to keep a level head throughout stressful times, think clearly and find solutions is one of the hallmark characteristics of a successful leader.

So what does this have to do with fasted cardio? We have known for years the cognitive, mental and mood benefits that come with regular exercise. In fact, psychiatrist and author Psychiatrist and author of Spark, John Ratey, has found that lifestyle habits appear to have the most profound effects on overall mood, especially morning exercise.

Here is an excerpt from a recent interview.

“Dr. Ratey has always had a habit of exercising in the morning. He has found the cognitive and emotional benefits of morning exercise stick with him long after the workout has finished.”

When we start moving, our heart starts pumping faster to deliver more oxygen to the working muscles. As our heart rate and breathing increase, our brains also require more oxygen meaning things start to “fire” a lot more efficiently. It’s not uncommon for people to have their best ideas when exercising, especially with something that doesn’t require you to be aware of your environment or that is stationary. You can close your eyes, listen to your favourite music and let the thoughts flow as you move your body.

If we know our day is going to be quite demanding, what better way to prepare than to get some early morning cardiovascular work that gets the heart pumping, blood flowing and most importantly, our brain firing on all cylinders.

The Power of Fasted Cardio On Mental Resilience


The American Psychological Association (2014) defines Mental Resilience as: “The process of adapting well in the face of adversity, trauma, tragedy, threats or even significant sources of stress.” In other words, you don’t get crushed when the stakes are high, YOU thrive off it.

Of course, there is a limit to how much stress anyone can handle but it’s safe to say that being able to increase this capacity is only going to help, especially when it comes to being a high performer.

When we exercise, we are artificially inducing a “stress response” as the hallmarks of training and stress are basically the same.

  • Higher heart rate.
  • Faster, more shallow breathing.
  • Higher cortisol and adrenaline.
  • Higher blood glucose levels.
  • Increased blood flow to the extremities.

When we weight train, these effects do happen but due to the longer rest periods and short bursts of intensity, it’s rare that you will stay in that state for extended periods of time. You know you have a good amount of rest coming up, even if you push yourself extremely hard for 1-2 minutes.

During moderate to hard cardiovascular training, these effects are sustained for much longer periods of time meaning you have to learn to ‘endure’ the discomfort to keep moving forward. Fundamentally, the more discomfort an individual can handle the more successful they are going to be in most endurance activities.

In fact, this study looking at pain perception compared ultra endurance runners to non athletes. The participants were told to place their hands in a bucket of cold water for as long as possible. The non-athlete group lasted 96 seconds on average while the runners all made it to the three minute safety cut off where they then rated the pain a 6/10. Not only were they able to withstand discomfort for longer, but the intensity of that discomfort was also much lower compared to the non-athletes. 

Why Does This Matter For You?


Think about how this trait can carry over to all areas of your life. When obstacles come your way in business or relationships, you want to be confident in your ability to be able to withstand setbacks, think clearly in times of stress and find a solution vs falling victim to these situations. What better way to “train” this capacity by challenging yourself physically on a regular basis, proving to yourself time and time again that you DO have the strength to show up and keep moving forward, no matter the temporary discomfort. 

The more you do this, the less excuses you will cultivate as to why you can’t do something, raising your own standards to much higher levels. For example, I will always do my 50 minutes of cycling each morning no matter how poor my sleep was the night before, how tired I am or how sore my legs are. There are mornings where my legs feel like lead but I will still show up and do the best I can, for that day. 

Funnily enough, I ALWAYS end up feeling accomplished that I did the session afterwards as it reinforced the following ideas: 

“I show up and give it my best no matter what”.
“I do what I need to do, even if I don’t feel like it at times”.
“I have the capacity to withstand discomfort and work through it”.

When something needs to be done or I need to meet a certain deadline, I know I have the ability to push, not give up and “lean in” when most people would get overwhelmed. 

What Type Of Cardio Should I Do?


From a structure, mood and productivity standpoint it doesn’t really matter what sort of fasted cardio you do. Simply walking at a brisk pace, ideally outdoors while the sun comes up, for 20-30 minutes each morning would be a great habit for anyone to start incorporating but if you were after the mental resilience aspect too, going for something that will elevate your heart rate (between 120-140bpm) for a sustained period of time would be advisable.

When it comes to cardiovascular training, it’s important you find an activity that you really enjoy and can see yourself doing for an extended period of time. This is why we aren’t going to provide you with a list of “the best fat burning exercises” but instead, urge you to find something that will meet the above criteria but most importantly, keep you wanting to come back for more.

We have many members who enjoy follow-along group classes, cycling, rowing, zumba, dance, running or just brisk walking. 

What Counts As Fasted?


To keep things very simple, anything that contains calories would “technically” put you out of a fasted state but throwing in a splash of milk into your coffee or a small amount of fruit (which is what I personally do as my sessions last closer to an hour) that equates to less than 50 calories is all good.

If your sessions are only lasting 20-30 minutes and are either a brisk walk or something more moderate, all you will need to consume prior to your session would be 100-150mg of caffeine, some water (~500ml) and 1-2g of salt.

If you are engaging in longer, moderately intense sessions on a cycle bike, elliptical, rower, stepper, etc that are between 30-60 minutes in duration, then consuming some protein in the form of essential amino acids (10g) or whey protein (15g) prior to your session may be of benefit in preventing muscle breakdown.

Also, don’t be afraid to flavour your water with zero calorie cordial as this has been shown to increase performance.

The Fasted Cardio Verdict


Anecdotally, all the benefits we have discussed today do seem to be amplified when performing the activity in a fasted state but it’s more due to the fact of placing the activity first thing in the morning vs some magical metabolic advantage.

Yes, there might be a slight advantage to doing your cardio fasted when you are trying to eek out every last percentage point towards the end of your checkpoint but the real “magic” lies in all the other areas it can enhance.

  • Your structure. Starting off each day by serving yourself before serving others.
  • Sets your circadian rhythm each day, allowing you to function at your best during the day and helping you wind down in the evening.
  • Enhances your mood and productivity, allowing you to show up in a superior state, leading to better decisions, outcomes and overall performance.
  • Builds mental resilience by proving to yourself that you can push yourself, overcome obstacles and show up even if you don’t feel like it.

If you’re looking for an edge, we think employing some fasted cardio into your routine is only going to have a positive impact on your overall performance with very little downsides. Try it out for at least a month where you commit to 20-40 minutes each morning (based on the examples mentioned above) and let us know how you get on!

Ivan GavranicIvan Gavranic

Ivan Gavranic is RNT’s Head of Applied Research, where his focus is on translating scientific research into real world practical applications for our members. As one of our leading coaches based in Australia, Ivan has lived and breathed transformation for over ten years, staying now at sub 6% body fat year round, he continues to focus on attaining calisthenic and gymnastic skills you only see in the movies!

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