Fasted Cardio

Is fasted cardio the magical solution to burning fat?


Or just another made-up fitness myth that needs go someplace like The Upside Down in Stranger Things and never return?


Blame it on Bill Phillips. Wait, what? you’ve never heard of him?


Jump in the wayback machine and travel back in time to 1999.


  • Fears about a worldwide computer meltdown dominated the headlines as the year 2000 approached, also known as Y2K. 
  • The mind-bending movie starring Keanu Reeves, The Matrix, was a blockbuster hit. 
  • Raised in a trailer park, the blond bombshell teen phenom Britney Spears dominated the charts with “…Baby, One More Time.” 
  • Millions of people stepped up to participate in the Latino-inspired fitness craze known as Zumba.


And then there was fitness guru Bill Phillips.


He published a booked called, Body for Life: 12 Weeks to Mental and Physical Strength.[1]


And while his approach to health and fitness is reasonable, he provided one piece of advice that is still being debated 20 years later.


His controversial advice: Crushing a 20-minute high-intensity interval workout on an empty stomach (fasted) when you wake up in the morning burns more fat that having a bite to eat and then completing a cardio workout.


Fasted cardio for fat loss, or just a myth?


If you’ve ever pondered this question, you’re not alone. It’s so-called benefits are on the Internet in perpetuity.


Countless fitness professionals, personal trainers, bodybuilders, and gym bros swear by the benefits of fasted cardio.


There’s a long list of explanations passed around about the benefits of fasted cardio, including your body burning more fat for energy instead of tapping into available carbs.


But is it really true?


Just as many denounce fasted cardio as nothing more than a fad that doesn’t have a significant impact on fat loss compared to cardio after eating.


So which is it?


Exercise science researcher Dr. Brad Schoenfeld and his team, including fitness pro Alan Aragon, had their opinions on fasted cardio. And they generally sided with the group that called fasted cardio a fad.


But without concrete evidence that disproves fat loss benefits of fasted cardio compared to fed, it was hard for any fitness professional to definitively take a side.


So Schoenfeld, Aragon, and a team of researchers decided to change that, set up a study, and get some answers about fasting, cardio, and fat loss once and for all.[2]


Study: Cardio Fasted vs. Fed for Fat Loss


Researchers recruited 20 healthy young adults, and completed a full work-up of body composition tests to begin the four-week study.


The Diet


Everyone received a customized meal plan intended to create a 500-calorie per day deficit for fat loss, along with ongoing nutrition counseling. But they were divided into two groups, fasted, and non-fasted.


The Workout


Both groups performed the exact same 60-minute treadmill workout three days a week during the four-week study.


  • 5-minute warm-up
  • 50 minutes of walking or jogging
  • 5-minute cool down


Group 1 – Fasted Cardio


People in this group completed the treadmill workout after an overnight fast.


Group 2 – Non-Fasted Cardio


People in this group drank a 250-calorie protein shake before completing the treadmill workout.


The Results


After the four-week study of dieting and training concluded, researchers conducted the same battery of body composition tests on the participants to measure results. Here’s what they found:


  • Weight loss. Both groups lost weight, around 2.2 to 3.5 pounds (1.0 to 1.6 kg).
  • Loss of fat mass. Both groups also showed improvements in fat mass and lost an average of 1.5 to 2.4 pounds of fat (0.7 to 1.1 kg).


And in both cases, the fasted-cardio group achieved slightly better results. But when researchers further evaluated the data, they also found no significant differences between groups for changes in


  • Body Mass Index
  • Percent body fat
  • Waist circumference


And that’s what Schoenfeld and Aragon hypothesized in the beginning.


True, this is a small sample size for a study, but researchers believe others would achieve the same results if they conducted a similar study to compare fat-loss between fasted and non-fasted cardio.


The Skinny on Fasted Cardio vs. Non-Fasted


The difference between fasted cardio and non-fasted cardio for fat loss are so small, they’re difficult to measure.


“The best advice for those who are simply looking to get lean is to focus on total energy and macronutrient balance, whether you perform cardio fasted or fed should depend entirely on preference,” says Schoenfeld.


In other words, what matters most is fitting in your cardio workouts when it works for you. Forget having an early-morning freak-out to fit in a fasted cardio session. It’s not as important as simply fitting in your cardio workout.


Hustle. Do the work. And you’ll lose the same amount of fat either way.





1. Phillips, B. (1999). Body for Life: 12 Weeks to Mental and Physical Strength. New York, N.Y.: Harper Collins.


2. Schoenfeld, B., et al. (2014). Body composition changes associated with fasted versus non-fasted aerobic exercise. Journal of the International Society of Sports Nutrition. From: