What is Fasted Cardio and Does it Work?

Emily Abbate
by Emily Abbate
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What is Fasted Cardio and Does it Work?

There are two types of people in this world: People who like to work out in the morning and people who don’t.

If you’re a member of Team Dawn Patrol, then you’ve probably chatted with a friend about fasted cardio. Simply put, this involves getting your heart rate up without eating anything prior. While most people do this type of activity in the morning, the fasted state can be achieved later on in the day as well.

THE BASICS OF FASTING

“A true fasted state starts at about 8–12 hours after your last meal,” says registered dietitian Allison Childress, PhD, a certified specialist in sports dietetics and assistant professor at Texas Tech University. “However, achieving a ‘fasted state’ can happen if it’s been 3–6 hours since your last meal. Most people who do fasted cardio do so in the morning before eating to ensure their body is in a completely fasted state.”

For some, doing fasted cardio happens in the early hours of the day, simply because they don’t have time to eat breakfast pre-sweat. According to science, there can be some benefits of getting after it sans fuel. People can burn up to 20% more body fat by exercising in the morning on an empty stomach, according to one study published in the British Journal of Nutrition. Another University of Scranton study revealed it may lead to reduced calorie consumption in the 24 hours that follow the fasted workout.

“The idea is that exercising in a fasted state burns stored energy (fat and glycogen) versus energy you have just consumed,” says Childress, who notes that this strategy works differently for everyone. While you may see your BFF lose fat from fasted cardio, you may not see any fat loss yourself.

FASTED CARDIO CAVEATS

Before you go running around without anything in the tank, there are a few things to keep in mind says Lindsey Clayton, a Barry’s Bootcamp instructor and co-founder of the Brave Body Project.

“Doing fasted cardio is safe, but if you’re going to do it you should keep the intensity of the exercise low,” she says. “Think jogging instead of a hard run or sprint.” Clayton cautions that if you find yourself light-headed, tire easily or feel as if you’re not working at the level you want to be — then exercising post meal or snack may be better-suited for you. In one Loughborough University study, runners who tackled a 60-minute treadmill session without eating first were more hungry than those who ate ahead of exercise

Ultimately, it’s all about your goals.

“Fasting cardio not only burns stored fat and carbs but can also burn stored protein in the form of lean muscle,” says Childress. “For most exercisers this is not desirable. Sipping on a BCAA (branched chain amino acid) drink during fasting cardio can alleviate some of this breakdown. Look for a supplement with at last 5g of BCAAs.”

THE BOTTOM LINE

As with any workout, make sure you’re placing importance on what you eat once you’re done. Fasting primes your body to take in nutrients once the effort is over, which means you should look for protein and carbohydrates to help refuel your muscles. The International Society of Sports Medicine recommends consuming .14–.23 grams of protein per pound of bodyweight very soon after a workout (that’s 20 grams of protein for a 140-pound woman).

The good news: There’s room to experiment. Feel out the right approach for you, whether or not fasting is part of the equation.

About the Author

Emily Abbate
Emily Abbate

Emily has written for GQ, Self, Shape and Runner’s World (among others). As a certified personal trainer, run and spin coach, she’s often tackling long runs or lifting heavy things. In addition to that, she’s working on Hurdle, a podcast that talks to badass humans and entrepreneurs who got through a tough time —a hurdle of sorts— by leaning into wellness.

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5 responses to “What is Fasted Cardio and Does it Work?”

  1. Avatar Zoe says:

    TW: self-harm
    What if you are diabetic? Does “fasted” include throwing away your drink? It does for my ex-friend (“ex” for reasons that will soon become obvious!) who practices this scarless form of self-harm (and has made me do so), so called to me because its consequences cause me total-body pain that can sadly become eerily satisfying if it lasts too long. Unfueled exercise makes my blood sugar (or at least my perception of it) drop well below what my doctor has said is my minimum survivable level (they say it’s 60mg/Dl, but FC drops me to what feels like 30-40. When I do it by mistake (usually having been conned into bed-bathing on empty due to my injury), the first thing to go is my ability to breathe sans dry cough (which once became a productive one and I was stuck for a while), followed shortly thereafter by my perception of space (read: I immediately become a fall risk). Then I’ll get dizzy, followed by nausea, followed by lightheadedness. Once all that’s over, my stomach begins hurting immediately and sharply. If I’ve had time to fight all those symptoms, I will either be more starving than before or (more often than not) have lost my appetite but need to eat anyway for my survival/before my perceived blood sugar drops into the single digits on me. It’s all kinds of scary, so I would ultimately say talk to your doctor (and maybe your therapist) before depriving yourself of whole meals.

    • Avatar La Bandita says:

      Then don’t do it!! You know you don’t have to do every thing you read, right!!? Right?? Also, there is certain level of health assessment you should do. If you’re have any medical condition don’t do the exercise. Every thing is not for everyone!!!

  2. Avatar Tom G. says:

    There’s a lot of peer reviewed evidence that fasted cardio does nothing more when compared to regular cardio and caloric deficiency. It’s calories in and out. This is just another way for people to try and make money through diet plans and attention-grabbing headlines.

    • Avatar Nicole Cutmore says:

      Confused about how you believe people can make money off suggesting someone try a workout prior to breaking their fast? I do an hour of fasted cardio 4x a week because it just feels better to me, no one is profiting off of that.

  3. Thanks Emily! Fasted cardio has some unique fat loss benefits. Research shows that exercising in a fasted state increases both lipolysis and fat oxidation rates. Lipolysis is the breaking down of fat cells for energy. Fat oxidation is the burning of this energy by cells. we can’t unequivocally say that fasted cardio is best for burning fat. Many studies on fasted or fed cardio focus solely on how many calories are burned during exercise.

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