Does Training Fasted Matter

by Dean McKillop 3778 views Training

Does Training Fasted Matter

We have heard it all before but the question still remains… what is better for fat loss, training fasted or training fed? Let’s delve into the pro’s and con’s of training fasted, discuss why training fed may be better or worse and then come up with some concrete suggestions on which is better or how we can implement either concept more effectively.

Why Fasted?

The notion of training fasted works on the premise that training without consuming any food prior to exercise enhances the breakdown and burning of stored fuel in the form of fats.

As opposed to fed, whereby the breakdown of food that was just consumed into available blood glucose would be used preferentially.

Given the individual who is training fasted has not eaten and more specifically, not consumed any carbohydrates, it is proposed that due to the lack of carbohydrates becoming available in the blood, the body has an increased ability to burn fat.

Which is all well and good in theory, but does it make a difference in the context of an entire day, week or even month of dieting? More than likely not…


You see, the body burns energy on a preferential scale that is based upon the intensity of the exercise.
The lower the intensity of the exercise, the greater amount of fats the body uses.
The higher intensity of the exercise, the greater amount of carbs the body uses.


In fact, it is generally recognised that up until the threshold of 60% of a persons heart rate maximum (the highest speed their heart can beat), fat is the primary fuel source being used to create energy. After you pass 60%, the use of fats for energy begins to reduce, while the use of carbs simultaneously increases due to the body’s ability to breakdown stored carbs (glycogen) and convert them into usable energy (ATP) far faster than it can fats.

Right, so it makes sense… if you want to burn more fat, do low intensity cardio fasted. Right? Well no, not really.

couple running

You see, looking at fat loss, exercise intensity and food consumption in such isolation fails to recognise the importance of contextualising dietary and training advice within the entire diet and exercise regime.

Because here is the kicker…While low intensity exercise burns more fat during exercise, it burns very little thereafter. Whereas high intensity exercises burns more carbs during exercise, but much higher fats thereafter.

So now it’s getting a little confusing…

  • Training fasted means we have low blood sugar levels and can use stored fat or stored carbs for energy. Remember the intensity changes this.
  • Training low intensity burns more fat during but very little after
  • Training high intensity burns little fat during but far more after
  • Training high intensity requires carbohydrates for energy but not fats

Furthermore, it has been postulated that high intensity exercise, during phases of low calorie dieting, when done fasted, increases the risk of muscle loss as well. And we DO NOT want that!

So now do we not only have to consider whether we train fasted or fed, the intensity of the exercise is also important.

One type of intensity burns more fat during, but less after, whereas the other burns less during and FAR more after, but it comes with an inherent risk of potential muscle loss.

And here is another kicker… increased muscle loss will result in a decreased ability to store fats.

Again I ask… are you confused yet? Hopefully, the answer is yes because that was indeed my intention. Sorry.

As you can see, and admittedly I’ve only just scraped the surface in comparing fasted vs fed vs low vs high intensity exercise, there are a tonne of variables and conflicting ones at that, which we need to consider.

The simple reality is this…
  • The calories you consume, versus the calories you burn, will determine whether or not you are in a net gain or a net loss of body weight - Eating fewer calories than you burn will result in weight loss
  • The macronutrients those calories consist of will determine if you are in a net gain or net loss of muscle tissue - Eating too little protein and carbohydrates will increase the loss of muscle
  • Your performance in the weights room will also determine how much muscle you retain or gain - Ensuring you maintain or improve strength is critical

Because of these 3 factors, your primary concern for determining whether or not you should train fed or fasted should be…

What makes you perform optimally?

If training fasted allows you to train optimally and not lose performance, then go for it. Likewise, if you need some food in your belly or some carbs in the system, have a small snack prior.

You see… Whether you burn more fat in the morning and less at night or vice versa, the end goal for fat loss is to lose more fat IN TOTAL by the end of the day. Over complicating how you burn fat throughout the day by targeting nutrient timing and exercise specificity, is largely micromanagement for the general population and is completely unnecessary when trying to lose body fat.

Train fasted or train fed, just make sure you eat and train appropriately on a consistent basis for the best results. 

Dean McKillop

Exercise Scientist

I completed my Exercise Science Degree at the University of QLD and have worked in the fitness industry for over 8 years, including a short stint at the Brisbane Broncos in 2010 as a student. I also hold my Level 2 Strength and Conditioning Coach accreditation (ASCA) and have competed in 1 bodybuilding season, placing 2nd at the IFBB u85kg Nationals.

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