Fasted cardio has become extremely popular lately. It’s all over social media with different “fitness icons” claiming that it’s the secret to their success. But is fasted cardio really that great? I decided to do some research to find out!
First lets start with the basics. What is fasted cardio? Fasted cardio is simply just exercising in the morning after fasting overnight (i.e. not eating breakfast before you workout). The idea behind it is that if you exercise on an empty stomach, you will accelerate the fat burning process. When you are in a fasted state, your body has low levels of both glycogen and insulin. Due to this, they will cause the body to shift energy utilization away from carbohydrates and towards fat. Therefore causing the body to use stored fat for fuel. Sounds great right?
I found a 2014 study published in the Journal of the International Society of Sports Nutrition that analyzed body composition changes during fasted cardio vs. non-fasted cardio. The study split it’s participants into two groups: fasted and non-fasted. All of the participants had been doing cardio exercise prior to the study, and non of them were considered obese according to their BMI. Both groups had to follow a provided diet that would put each of them at a caloric deficit, in order to elicit weight loss. Both groups had to perform 1 hour of steady state cardio, 3 times per week, on a treadmill. The results of the study were pretty shocking. “Although both groups lost a significant amount of weight and fat mass, no differences were seen between conditions in any outcome measure regardless of pre-exercise feeding status” (1). This means that your exercise level and overall caloric intake makes a difference with fat loss, and not the timing of your meals in conjunction to your workout.
Despite not seeing a change in fat loss, fasted cardio has also been noted to impact lean body mass gains! An article posted by the National Strength and Conditioning Association found that “[cardio] training with depleted glycogen levels has been shown to increase proteolysis…the strategy has potential detrimental effects for those concerned with muscle strength and hypertrophy” (2).
So overall there is no real benefit to fasted cardio. So go ahead and eat your breakfast before your next workout! Who knows…it might just give you even more energy to work harder in the gym!
1) Schoenfeld, Brad Jon, Alan Albert Aragon, Colin D. Wilborn, James W. Krieger, and Gul T. Sonmez. “Body Composition Changes Associated with Fasted versus Non-fasted Aerobic Exercise.” Journal of the International Society of Sports Nutrition 11.1 (2014).
2) Schoenfeld, B. (2011). Does Cardio After an Overnight Fast Maximize Fat Loss? Strength and Conditioning Journal, 33(1), 23-25.