Should I be Doing Fasted Cardio?
We get it. You wake up in the morning, check your Instagram feed, and get an immediate guilt trip after reading a series of posts full of sweaty, smiling selfies exclaiming, "Just finished my fasted cardio!"
You might be hearing a lot about fasted cardio on social media and at the gym; enthusiasts gush all about how fasted cardio is the fastest and most effective way to burn off body fat.
If everyone's doing it, and they look so good, it's hard not to think, "If I want that body, I need to do what they’re doing." But is fasted cardio for you? What’s the real deal? Does it work, and if so, how do you do it?
The idea behind fasted cardio is getting your sweat session in first thing in the morning, before you'd had anything to eat, while your body is still in the overnight fasting state. The theory goes something like this: If you work out on an empty stomach, the calories you burn during your workout will be from your fat stores, as opposed to burning off the calories you ate for breakfast.
Can it be that simple? Well, not really.
Fasted cardio is one of the most misunderstood fitness techniques these days. You might read online that you’ll burn about 20 percent more fat on an empty stomach than you will when you’ve been fueled by recent food intake. The reason for this, say proponents, is that when you’re in a fasting state, your body tends to hang on to its carb stores for energy, and will favor letting go of fat to fuel your movement. Furthermore, the low insulin levels associated with fasting favor fat breakdown, which means fat is used for energy during the workout. But one problem is this: along with releasing these fat stores, fasted cardio also tends to release more amino acids as well, which isn’t what you want if you’re trying to hang onto or build muscle.
Here’s another problem: studies looking into this phenomenon mainly measure the amount of energy burned during exercise only. And of course, this isn’t all we care about, because so many benefits of exercise happen to us after (not during) the workout. Fasted cardio doesn’t appear to offer us any metabolic benefit post-workout, while other methods—such as HIIT—do.
Keep in mind that food is, of course, your fuel. Your body metabolizes the food you eat to power it to do everything: breathe, grow, think, exercise. Your body slows down your metabolism overnight while you sleep to give it the opportunity to rest and repair itself.
Eating breakfast is what tells your metabolism to wake up and get to burning those calories again. You are literally breaking your overnight fast (which is where the term breakfast comes from). Breakfast also sets the stage for your day: it stabilizes your hormones and blood sugar levels, which help to control food cravings all day as well as regulate your energy levels and your mood. Some studies even show that people who eat breakfast regularly weigh less than those who don’t.
Another benefit of doing cardio without fasting is that you might find you feel better, so you will push harder and accomplish more, overcompensating for the fat burn simply by burning more calories, which is ultimately more helpful in your weight loss efforts. (Plus you’ll enjoy your workouts more, which is invaluable!) So what you might gain in fat burning you lose in increasing fitness and your ability to burn fat at higher intensities in the long run.
Most people who successfully use fasted cardio as their training technique are people who aren’t worried about anything other than shedding those very last few pounds, like fitness competitors or those seeking the physique of one. Some studies suggest that fasted cardio may set you up for failure because even if it does burn more fat DURING exercise, you may overcompensate calories later. For most people, any effect is likely negligible; the compensatory mechanisms at play wash those effects out in the end.
If you have more than a few pounds to lose, eat breakfast! It's the most important thing you can do to get your body running efficiently. Unless you are in contest prep mode, where every calorie and ounce of body fat can make the difference between first and second place, don't torture yourself thinking fasted cardio will melt your body fat off.
If you want to give it a go, try it out and see how you feel, but I you feel dizzy, weak or nauseous, stop. Define fitness by what works for you, not by what anyone else is doing.
Bottom line: if you do well on fasted cardio and enjoy it, keep doing it. But don’t choose it at the expense of missing out on other types of exercise, like HIIT, weight training, or cardio after a pre-workout meal, or of greater workout enjoyment.
SUBSCRIBE TO NEWSLETTERGet our 7 Day Head Start E-book for FREE!