You’ve probably read about fasted cardio a million times on the internet and within the pages of this magazine. That’s largely because the vast majority of the leanest physique athletes swear by the practice, as do those who have lost large amounts of weight. If you didn’t flip through a single research journal, it sounds like it makes sense, right? In the absence of food to use as fuel, the body must go on the hunt for alternative sources—in this case, body fat—during the workout and subsequent recovery. But does the anecdotal evidence that fasted cardio works hold up to the available science? Let’s dig in.
WHAT IT IS
Fasted cardio is the practice of performing cardio—usually at a lower intensity on a bike or a treadmill— on an empty stomach, first thing in the morning.
Those who adhere to fasted-cardio regimens report achieving lower body-fat levels while retaining more muscle mass.
A 2014 study in the Journal of the International Society of Sports Nutrition compared fat-loss results between two groups of hard training athletes, one of which was fed beforehand, while the other trained on an empty stomach. There was no difference in fat loss between the two groups. What’s more, a 2011 study found that a light pre-workout meal was actually preferable to fasted cardio for greater lipid (aka fat) utilization. Go fi