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Health Myths Debunked: Fasted Cardio Burns More Fat Than Fed Cardio

Monica Salafia MS, RD, CPT

The Myth

Not eating before a workout burns more body fat and we lose weight faster.

The Background

We often hear about the “fat burning zone” in fitness so it seems logical that if we don’t eat before a workout and stay in the fat burning zone, we will only use body fat to fuel our workouts. This is a good example of how a kernel of truth gets overblown and becomes nutritional dogma.

The Facts

Fasted cardio does not burn more fat or cause people to lose more body weight any more than doing cardio in the fed state. Losing weight and/or body fat is all about a total hypo-caloric deficit.

A small study published in the International Journal of Sports Nutrition studied the effects of fasted cardio versus fed cardio in a group of 20 healthy females (1). All study participants were given a calorie goal that would induce weight loss. The only difference was that some of the participants did fasted cardio while  the others had a meal. This study showed there were no differences in body weight or body fat changes between the two groups.

The key nutrients providing energy during exercise are carbohydrates (in the form of glycogen) and fat. At all times the body is using a “fuel mix” that includes both carbohydrates and fat. However, when exercise intensity goes up, the need to use carbohydrates goes up because it can produce energy more quickly (2).  

To ensure we burn mostly body fat and not muscle, it’s important to keep a supply of glycogen in our muscles that we can use for fuel instead of protein.

Over time, training with a lower caloric intake may limit our ability to keep up with a fitness routine, lower our performance, and can cause a loss of muscle mass. Since muscle mass burns more energy at rest than fat, we want to preserve as much muscle as possible when trying to lose weight (3).

The Bottom Line

Overall energy balance (energy in versus energy out) will determine weight gain, loss, or maintenance.

Running, walking, and cycling are all forms of aerobic activity that will burn additional calories. If motivation levels are higher in the morning before eating breakfast then maybe fasted cardio can work for you. If you have more time and energy in the afternoon to get your cardio in, then that’s also great! Whether we are in the fasted state or not, it is the overall calorie deficit that will cause weight loss and body composition changes.

11 thoughts on “Health Myths Debunked: Fasted Cardio Burns More Fat Than Fed Cardio”

  1. Lily Grozeva says:

    That was useful. I was one of the don’t-eat-before-workout girls.

    1. Monica says:

      So glad you found it helpful! Eating before a workout may be the better choice in the long-term, especially when trying to make your fitness routine sustainable! What are you favorite go-tos for pre workout snacks/meals these days :)?

      1. Lily Grozeva says:

        This winter I have either smoothie with apple, ginger, beet, cucumber and parsley; omlette with spinach; or a bowl of kefir, granola and some berries. Now I started to introduce fruits here and there as spring emerges 🙂

        1. Monica says:

          Oh yum!! That’s one of my favorite parts of spring and summer all of the fresh fruit that is available. Your apple ginger smoothie sounds so refreshing! I’ll have to give that a try!

  2. Jessica says:

    This message is not about the topic. I have been trying to contact the Noom Team since monday and no news (4 e-mails sent). The App is great but the support team is clearly not keeping up…

    1. Monica says:

      Thanks for sending the emails! It’s the best way to contact them for sure. I don’t think they will see the message on the blogs though :/ . There is also a time stamp on the emails you send so all of your messages will be read in the order they were sent.

  3. Michael Hungerford says:

    The paragraph about keeping glycogen stored in your muscles in order to spare muscle tissue is the primary reason I dont buy this whole Keto cult that people are all about now. Carbs are what the body uses to produce glycogen.

    1. Megan says:

      If you researched a ketogenic diet you would learn that you are correct, the ketogenic diet does not allow your body to produce glycogen. You don’t need it either, because your body begins to use fat for fuel completely, called ketosis. It isn’t a cult, it’s a diet that works incredibly well for those that need to lose a large amount of weight. I lost 70 pounds and am keeping it off for the first time ever. No calorie restrictive diet has ever provided me these sorts of results. Anyway, good luck on your health goals.

  4. Sky Lilly Simpson says:


  5. Tamieka Fagg says:

    Just cancel the subscription through your card company or bank! And possibly get refunded your money!

    1. Christoph Suwelack says:

      I will have to do that. I will cancel CC and get a new one. Then I have to enter every service I am paying with this card, in order to re-register.. I have to work in order to get the incompetence of Noom straight

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