By Andrew Menechian
Is fasted cardio for enhanced fat loss a myth?
The short answer is yes! Thank you for reading. But no seriously, the most important factor to determine a cardio protocols fat loss effectiveness is calories burned. It all helps from an energy balance standpoint.
For example, if you’re maintaining your weight on 2500 calories, and now incorporate 500 calories worth of cardio, then you are in a 500 calorie per day deficit. Now whether this comes from doing cardio in a fasted or fed state is irrelevant.
A 500 calorie deficit is a 500 calorie deficit period!
The myth stems from the idea that you will burn more fat if your body is using fats as a fuel source as opposed to carbohydrates. While it is true that you will be in a “fat burning state” when fasted, it is irrelevant in terms of fat loss, as energy balance is the key driver here.
Effects on body composition
A study performed on 20 ‘fit’ females in 2014, had all test subjects put into a calorie deficit for 4 weeks, meaning they were eating less than they burned. One group were directed to have a shake before their cardio and the other had the same shake after their cardio. The study found no significant differences in fat loss between the groups.
Are there any good reasons to do fasted cardio?
Yes, but not for body composition. Fasted cardio has been shown to enhance whole body glucose tolerance and increase insulin sensitivity.
Fasted cardio also appears to lead to chronic molecular adaptations favouring fat oxidation. This has no impact on body composition, but it should be of interest to athletes in sports where preferential fuel substrate utilisation can give them an edge, such as endurance athletes.
If fat loss or body composition is your goal, then fasted versus fed cardio makes no difference. Your main focus needs to be on creating an energy deficit.
If you’re doing a sport where fat is the preferential fuel substrate and you’re wanting to increase your performance, then you may receive a benefit from fasted cardio.
Yours in health,
Clean Health Fitness Institute
-  https://www.ncbi.nlm.nih.gov/pubmed/25429252
-  https://www.ncbi.nlm.nih.gov/pubmed/21051570
-  https://www.ncbi.nlm.nih.gov/pubmed/18276898