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What Is Fasted Cardio?

3 min read

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Remember all those times you hit the gym or went for a run first thing in the morning? The mental fortitude to get out of bed and exercise is all consuming. Food isn’t on your mind or maybe the thought of forcing sustenance down your throat makes you want to blow chunks? Maybe time is of the essence? So you go skip those bananas or energy bars and exercise on an empty stomach?

Is this really healthy? Is it effective?

What Is Fasted Cardio?

It’s really simple. It’s doing cardio/working out without eating for a period of time.  

People may think that skipping lunch or dinner then exercising is fasted cardio, but really, science says differently. It actually takes 10 – 14 hours without food for the body to be in “fasting mode”. For most individuals (unless you’re one of those on the graveyard shift), fasted cardio takes place first thing in the morning.

What's all the hoopla about exercising on empty?

Glucose is fuel for the body. If there is excess glucose, the body stores it in the liver and muscles (the stored form of glucose is called glycogen). When the body is in a fasted state, there is less glycogen available. The body then goes looking for other forms of fuel. It may start to burn the stored fat. After only a little while of fasted cardio, the body has used the glycogen stores and then can start burning that pesky fat. This means that the percentage of fat burned during fasted cardio is slightly higher than doing cardio after your body is fed.Astudy published in theBritish Journal of Nutrition showed that people who ran on a treadmill in a fasted state burned 20 percent more fat than those who had eaten. An olderstudy published in theJournal of Applied Physiologyfound that people that habitually trained in a fasted state over the period of six weeks showed more improvement in endurance than those who ate before working out.

Cons of Fasted Cardio

It seems like people fixate on fasted cardio because of the two benefits of burning more body fat and the improvement in endurance. What needs to be mentioned is that in either scenario, fasted vs not fasted, the amount of calories burned will remain the same. It’s not guaranteed that the body will turn to burning fat for fuel first. Another option the body can choose is burning protein. That means that all the people who fight so hard for those bulging muscles could risk breaking them down.Strength and Conditioning Journaldid a study that showed that running when fasted broke down muscle protein two times more than running without fasting.

Research also shows that both the intensity and the amount of training/repetitions can be negatively impacted by doing fasted cardio. When the body doesn’t have carbs to use as fuel, it is more difficult to workout at the same level of intensity. You just won’t have as much energy to be able to put in the work.


What About Performing Fasted Cardio As A Weightlifter Or Bodybuilder?

Whether or not fasted cardio works for you in your weight lifting program is fully dependent on your goals. Is your primary object for this season to gain muscle mass, i.e. to bulk, and/or increase your strength? (Maybe you're trying to gain mass in your glutes?)

Performing cardio fasted is probably not going to be your best bet.

We’d strongly suggest a combination of short duration, HIIT style training combined with some slow, casual walking if you’re trying to get bigger and stronger. Interestingly, that’s also our recommendation for general health and well being as well!

If you’re on an aggressive cutting program, meaning you’re trying to lose as much body fat as possible while maintaining the maximum amount of muscle you’ve built, probably while on a bulk, fasted cardio can be an amazing addition to your workout program. Though as a general rule, we haven’t found it completely necessary unless your getting into contest prep level cutting. 

Is Fasted Cardio For You?

Consider your schedule. Weigh out what works best for you. It could be that catching those extra zzzz’s is more important for your body. Or maybe you’re more motivated to pound the pavement in the morning? If you decide to do it fasted, sports dietetics suggests not to exercise more than 90 minutes. Limit the amount of intense workouts when fasted. Or just wait 1-3 hours after breakfast so your body is fueled and ready to perform at your peak. Mentally and physically, your body will feel much better.

Either way, choose the programming that best fits your overall goals and is the most sustainable for you long term.

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