What is 'Fasted Cardio' and How Does it Affect Your Body?

What is 'Fasted Cardio' and How Does it Affect Your Body?

If you’re always looking for the next best way to boost your weight loss, you might be interested in fasted cardio. This technique—which is simply doing cardio while you’re fasting—leads to greater fat loss in some people, and weakness or dizziness in others. When you’re already on a intermittent fasting diet, however, it could be a great way to get faster, more dramatic results.

As always, talk to your doctor before starting a new workout routine or diet. If you decide to try fasted cardio, listen to your body above all. If it feels like you’re dizzy or about to faint, stop what you’re doing and rest.

Here’s an overview of fasted cardio and why some people are successful with the technique.

What is fasted cardio?

Fasted cardio is cardiovascular exercise performed when you’re in a fasted state. This usually occurs about four to six (or more) hours after you’ve eaten your last meal or snack. Some people do this by getting up to work out before they’ve eaten breakfast. This can make it a little easier than if you were consciously fasting all day. Hanger isn’t conducive to great workouts!

Keep in mind that some experts advise that a “true” fasted state—that is, when your glycogen levels are low—you may have to fast nine to 10 hours first. This forces your body to go through its carbohydrate sources, then start turning to fat for fuel instead.

How does fasted cardio affect the body?

The idea behind fasted cardio is the same one that propelled the Atkins diet to great fame in the 1990s: your body uses carbohydrates for fuel first. In the absence of carbohydrates, your body has to start using your stored fat for energy. Therefore, proponents theorize, not having any carbohydrates in your body to fuel your workout will force your body to burn additional fat. It’s like a dietary BOGO deal.

Research shows that this may indeed be effective: one study found that “aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.” Plus, when you’re finished with the workout, your body continues to pull energy from your fat stores to help you recover. This can raise your metabolic rate for up to 24 hours. In other words, this is a pretty efficient way to achieve fat loss.

If you tend to get nauseated when you work out after you eat, this is a good solution. You can still have water and coffee beforehand, but wait to eat breakfast until after your workout. (At that point, try to eat a lot of protein and complex carbohydrates.)

Of course, there are drawbacks to fasted cardio. Many people feel sick, dizzy or faint if they work out on an empty stomach. Unless your fitness goals include “recovering from a minor concussion,” make sure to listen to your body. If you feel a lot weaker than normal, stop the activity, rest, eat a small meal and try again. You may have better luck with fasted cardio right after you wake up, when we naturally feel more energetic.

A related drawback is that the weak feeling might cause you to stop earlier, or decrease your workout’s intensity. That won’t burn as many calories as it would have normally, even with the benefits of using fat for fuel.

Finally, fasted cardio could lead to muscle breakdown—so if you spend most of your time on social media bragging about your #gains, this could be detrimental to your goals. Some studies have indicated that the body may break down muscle tissue for energy instead of jumping straight to your fat stores. Bodybuilders beware.

Deciding whether to try fasted cardio

When you talk to your doctor about this weight loss method, make sure to ask them about how any pre-existing conditions might affect your results. People who are prone to dizziness and issues with low blood sugar should be especially cautious.

If you’re ready to try fasted cardio, go for it! The best way to begin is to start with mid-length, moderate intensity workouts. If you feel confident in your ability to push it harder over time, slowly increase the length and intensity until you reach your goal.

Should fasted cardio not work for you, not to worry. There are plenty of other workouts and healthy diets that can help you reach your fitness goals.

Back to blog