The method of fasted cardio has been around for ages now, always made more popular by social media “influencers” and professional bodybuilders.
But what exactly is fasted cardio? Fasted cardio is performing exercise (aerobic in this context) while in a fasted state. Fasting by definition is
Fasting is the willful refrainment from eating for a period of time. In a physiological context, fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal
The Theory on fasted cardio is that by being in a fasted state it causes your body to utilize fat stores as an energy source rather than its preferred energy source of carbohydrates. Because of this thinking fasted cardio has been thrown around for ages now as a great way to lose extra body fat.
The biggest problem with this is there isn’t a lot of evidence out there to support these claims other than anecdotal claims. In a study by Schoenfeld et al.  in 2014, the researchers had 2 groups of 10 females aged 22.4±2.8. Both groups were to perform one hour of supervised steady state aerobic exercise 3 times a week with one group being in a fasted state while the other group had a meal replacement shake prior to exercise. Both groups had their calories controlled and were put into a 500kcal deficit for the purpose of this study. While both groups had loss of fat mass, neither group had a significant advantage when compared to each other.
This brings weight-loss back to its baseline equation of “Calories in vs Calories out” . This means that the ability to lose weight means you will need to consume less calories than exerting through NEAT (Non-exercise activity thermogenesis) and aerobic/anaerobic Exercise. The big take home from this on whether to do fasted cardio or or not is this. Do what you enjoy more. Both will lead to the same desired outcome.
Now we need to keep in mind that Schoenfeld et al. study  is only one study. The biggest bit of advice from the author here is that you need to do what makes you feel better and will allow better adherence to a diet & training program.
Article written by Timothy Steward
· UFQ Strength & Conditioning Coach
· UFQ Sports Nutritionist