Is fasted cardio better for fat loss?

Several strategies are used to help reduce body fat with fasted cardio being one of them. Bodybuilders have been doing it for years to help shed weight in preparation for the stage... even I used to do it, and arguably still do

What is fasted cardio? 

So we are all on the same page, fasted cardio is traditionally seen as low intense, longer duration bouts of exercise (usually 20 minutes plus) just after waking up and prior to breakfast. The typical method of fasted cardio is usually done through walking/jogging as it's the most easily accessible, but any other low intensity exercise such as cycling, rowing etc can be performed. 

The Theory

Its believed that through doing cardio prior to eating food will help increase lipolysis (oxidation of body fat).

And to a certain degree this is true

What we must understand that the body is ALWAYS burning and storing body fat simultaneously . It isn't like a light switch that is either in or off. When you eat, you're in a calorie surplus and storing body fat (lipogenesis), and during times of being unfed, you're in a deficit and reducing body fat (lipolysis). 

The longest time we in an unfed state is throughout the night when we are sleeping, it is during this time we will be burning the higher percentage of body fat. 

Through prolonging this unfed state, yes, we will oxidising more fat, regardless of adding in cardio, usually low intense steady state (LISS) or not.

As mentioned earlier, low intensity cardio is usually performed as the this type of cardio keeps us in the 'fat burning' zone which is between 60% and 70% of our maximum heart rate. With insulin (which I'll get to) being low and a combination of working in this 'fat burning' zone, this has caused the belief that it's a golden time to increase the utilisation of body fat.


Another reason that fasted cardio has been touted as a fat loss wonder is that insulin is low during this period. Insulin is a protein hormone released by the pancreas and is necessary for the metabolism of nutrients. It has been given some bad press and is seen as the 'fat storing' hormone and should be kept low.

Whilst Insulin does inhibit fat loss whilst in a fed state, we must remember that we are not always in a fed state. When we eat, particularly carbohydrates and Leucine (an amino acid that is key in maximising protein synthesis) rich proteins, insulin will rise and effectively stop the burning of body fat, this is due to the body now being in a fed state therefore it has no need to tap into stored body fat. 

Now I know what you're thinking...  If insulin is increased through carbohydrate consumption, then eliminating carbs will stop this fat preventing hormone and allow for more body fat to be burned... it sounds good on paper yeah?

Unfortunately our body has multiple mechanisms to detect whether we are in a fed state or not, and whilst insulin may not rise as much after a high fat meal, our bodies will cease the oxidation of body fat and use the readily available energy as its preferred fuel source.

Carbohydrates also play key role in things that help regulate body fat like Thyroid function an Leptin, so eliminating these in the short term may result in weight loss (not necessarily fat loss), but most people struggle to adhere to this diet strategy in the long term and can eventually rebound. Don't forget that carbohydrates are very important for performance, so eliminating these will effectively reduce the training effect we want in the gym 

Look at the big picture

When it comes to fat loss, OVERALL ENERGY BALANCE matters. How many calories we consume vs. how many calories are expended (look back on other blogs as I've wrote about energy balance several times in the past).

It's what happens over a 24 hour period over a sustained period of time that truly matters when it comes to fat loss.  

Whilst insulin does rise and fat burning is greatly reduced after a meal, after 2 or 3 hours it'll drop and the body will increase the oxidisation body fat as a fuel source.

I find the majority of people focus on minor details and neglect to look at the other, often bigger contributing factors that will assist in fat loss such as stress management, sleep and nutrition.

Stress management  

The psychology of the individual must be questioned when it comes to chasing fat loss. I find those that are throwing in excess cardio is done more through desperation than anything.

Another thing to consider is sleep... I keep saying I'll do a post regarding the importance of sleep but I want to make sure I know enough myself before breaking it down into a blog for you guys. For now, just understand that sleep is really important.

If you're setting the alarm early to perform cardio and missing out on vital sleep, this could be counter productive as it can lead to decreased expenditure later in the day, increased hunger signalling and worse performance in the gym.

The Hierarchy when it comes to fat loss

Cardio should be used sparingly when it comes to fat loss and can do more harm than good if over done. The priority should be shifted into other areas, here's my hierarchy when it comes to fat loss from most to least important:

  1. Sleep & stress management (this will effect everything below)
  2. Nutrition (managing the total energy consumed from food)
  3. NEAT (general movement)
  4. Resistance training (train like you were trying to build muscle)
  5. Cardio
  6. Supplements

Quite often I see people tackling this the wrong way round, wasting money on expensive supplements and pounding cardio. 

So... should I do fasted cardio?

Back to the original question... and answer is simple, and it all comes down to sustainability.

If the early morning is the only time that you have in order to help create a further deficit then that's fine. Like most protocols, it's down to the individual whether or not 'it works'.

It can also be a great way to start the day as an opportunity to start on the right food. I believe a good morning ritual (not like sacrificing a goat) is key, whether it's food prep, going for a walk, meditation, etc. Personally, I enjoy a walk with the dog for about an hour early in the morning, I listen to my podcasts, think about posts, business and life (I'm getting all hippy on you now). I don't think of it as fasted cardio and certainly don't credit it towards any fat loss that may have occurred, but just one of many contributing factors, it's just part of my normal habitual behaviours.


I believe if you're wanting to do anything to a high standard and get the absolute maximum return from your session and a greater calorie burn, it's best to do that in some form of fed state. Adequate recovery (sleep), nutrition and hydration promotes high performance in and out of the gym. 

But saying that, if it's the only time you have, it's convenient, you enjoy it, if it's not a stress or having a negative impact on any of other areas of your life, then do as you please. The beauty of fitness that there's all sorts of different tools that can be utilised for different people with different situations. Like nutrition, the training protocol must fit the person, not the other way round. 

Seeing the big picture and having a plan will give you a better understanding of how to manage your body composition. If the plan is to extreme and difficult even in the short term, then it's very likely it will fail in the long term.


If you'd like any further help, we offer online coaching where we can help manage your exercise and nutrition based on your lifestyle and requirements. For enquiries, please contact us.  

Thanks for reading. And as always, please feel free to leave a comment

Ian Bickle
2B-Fit Coach