At the most basic level, fasted cardio involves increasing your heart rate without noshing on a pre-workout meal or snack beforehand. Fasted cardio fanatics claim the practice maximizes your fat-burning potential. But, naturally, you might wonder whether working out on an empty stomach is a good (and safe!) idea or just a trend that sounds legit.
The idea of waking up crazy early, skipping breakfast, and dragging our butts to the gym or spin studio is enough to make us want to hit the “snooze” button, throw the duvet over our heads, and Seamless an egg sandwich to our beds.
Believe it or not, there are many people who swear by early workouts without fueling up first, because they believe that “fasted” workouts are better for you and could actually burn more fat.
Heading up the “fasted cardio” club? Jennifer Lopez and Alex Rodriguez, the fittest couple in Hollywood, of course.
“Another beautiful day in New York City, about to go do a little fasted cardio,” A-Rod said in his Instagram Story on Wednesday, walking alongside J.Lo. “That means cardio before breakfast. This is from our trainer, Dodd.” (“Hi, Dodd!” J.Lo playfully adds.)
The Basics of Fasted Cardio Workouts
First things first: How long do you have to go without food for your workout to be considered “fasted”?
Usually, eight to 12 hours, says sports medicine specialist Natasha Trentacosta. M.D., of Cedars-Sinai Kerlan-Jobe Institute in Los Angeles. But for some people, it may be just three to six hours, depending on how fast your digestive system is working and how much food you ate at your last meal. “Once the body has stopped processing and breaking down food, your insulin levels are low and there’s no fuel (glycogen) circulating in your blood,” says Dr. Trentacosta. As a result, your body has to turn to another source of energy-usually fat-to power you through the workout.
Typically, fasted cardio happens in the morning (after an overnight fast). But a fasted state can also be achieved later in the day (for instance, if you’re doing intermittent fasting or skipped lunch), says sports medicine dietitian Kacie Vavrek, M.S., R.D., C.S.S.D., of The Ohio State University Wexner Medical Center.
Bodybuilders have been using fasted cardio as a fat-loss technique for years, and regular gym goers have recently been adopting it as well. But you may have been doing fasted cardio workouts already without realizing it. Technically, any time you head straight to an early-morning workout without eating first, you’re doing a fasted workout.
The benefits of fasted cardio
Cardio might help you burn more fat throughout the day, trainer Danielle Natoni tells Health. The idea is that when you work out when you haven’t eaten recently, you are burning fat—aka stored energy—versus the energy from the food that you just consumed, she explains.
Cardio is actually Natoni’s preferred method of exercise. “On the rare occasions where I find I have to exercise no longer fasted, I feel slower and more sluggish,” she says.