Fasted Cardio.

Yay or Nay..?


Does fasted cardio help burn more fat?


You may have heard the term “fasted cardio” thrown around in the health and fitness world, especially on social media. But what does fasted cardio actually mean and does it really make a difference?


First, let’s talk about fasting…

Fasting is defined as abstaining from food or refraining from eating. Generally, you will naturally fast overnight while you are asleep because you are having a break from eating between dinner and breakfast. After you eat, and your body has broken down the food, it will start to store some of the components of the food, such as the macronutrients to use for bodily functions. Carbohydrates are converted into a form of sugar called glycogen, and this is stored in the liver and muscle tissue for later use. When your body needs it, the stored glycogen is then broken down and used in many chemical reactions within the body to make the energy it needs. Once the body’s glycogen stores start to get low it, the body will begin to break down fat into fatty acids that are then used to make the energy it needs – and this is what has driven much research into fasted exercise for fat burning.


What is fasted cardio?

Fasted cardio is cardiovascular exercise that is performed after a period of fasting. Put basically, you would be doing fasted cardio if you went for a walk or a run when you wake up in the morning and before you have eaten anything to break the fast you’d been doing while sleeping overnight. 


So does fasted cardio burn more fat?

There have been many studies over the years to determine if engaging in fasted cardio helps individuals to burn more fat. Many early researchers had predicted that exercising while fasted would increase lipid (fat) storage utilisation. They thought that once glycogen stores were depleted and the body turned to fat for energy, the more fat that would be used and therefor “lost”. Unfortunately, many studies have been conducted to find out whether this is the case, but so far the conclusions have not been in favour of this hypothesis. Although the science behind this theory is correct, the reasons for fat lost in the trials were not able to be put down to fasting alone.


So what does burn fat?

Recent studies on fasting and fat loss compared groups of people who exercised while fasted and those who did not. These studies actually concluded that regardless of fasting or not, any of the participants who were in a caloric deficit and participating in high intensity interval training had the best results in terms of fat loss over the period of the trial.


Studies have shown that it is optimal to consume a small meal before exercise (to optimise performance) but if working out in the morning while fasted works for you – by all means, do it! (I know that I can’t eat before working out if I’m hitting up the gym as soon as it opens at 5:30am).


Just understand that working out while fasted has not been proven to increase fat loss, while a caloric deficit and regular exercise is proven.


For more tips on eating for fat loss – check out the Complx Nutrition article on Intermittent Fasting.

Written And prepared by Tahlia: Follow her @Taliahshealthdiary​



1. Fasting – definition. Oxford Languages. Oxford University Press (2020).

2. Schoenfeld, B. J., Aragon, A. A., Wilborn, C. D., Kroeger, J. K. & Sonmez, G. T. (2014). Body composition changes associated with faster versus non-fated aerobic exercise. Journal of the International Society of Sports Nutrition 11:54.

3. Paoli, A., Marcolin, G., Zonin, M., Sivieri, A. & Pacelli, Q. F. (2011). Exercise Fasting or Fed to Enhance Fat Loss? Influence of Food Intake on Respiratory Ratio and Excess Postexercise Oxygen Consumption After a Bout of Endurance Training. International Journal of Sport Nutrition and Exercise Metabolism. 21:1 (48-54).

4. Trapp. E. G., Chisholm, D. J., Freun, J. & Boutcher, S. H. (2008). The effects of high-intersity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity. 32:4. (684-691).

5. Whitney, E., Rolfes, S. R., Crowe, T., Cameron-Smith, D. & Walsh, A. (2017). Understanding Nutrition. Cengage Learning Australia. Melbourne, Victoria.