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Does fasted cardio actually work?

 Does fasted cardio actually work?

Everyone has their opinion when it comes to the benefits of fasted cardio.

“Fasted cardio” simply means you do your cardio before you’ve eaten anything for the day. Some people swear by it. The idea behind it stems from the assumption that if you don’t have food in your stomach when you perform your cardio, your body will burn more fat than you would if you had eaten breakfast first.


Is this true? Does getting your cardio in before you eat breakfast have any impact on fat loss?

This idea has been debated hotly in fitness circles for years.

Let’s take a close look at what the research says, along with some caveats for what you should do personally.


Does fasted cardio burn more fat?

A study was conducted 10 years ago at the British Journal of Nutrition studying the differences in fat burned via cardiovascular activity in a fasted state (first thing in the morning without breakfast) versus a fed state (after breakfast). The results were surprising.

The 12 active males who were used as subjects all found similar results. Performing cardio before eating any food actually did burn up to 20% more body fat than performing cardio in the fed state. This caused fitness enthusiasts everywhere to change up their routines and start doing their steady state cardio first thing in the morning, before consuming any food.


Since that study, a few additional studies have shown the same thing. “Cardio” in these cases were defined as a 30-45 minute steady state jog or run on the treadmill.

On the surface, this appears to be a no brainer.


If we want to burn more body fat, we should do our cardio before eating, right?

Before you solidify this conclusion, there are a number of caveats to consider.


Issues with fasted cardio

As with any controversial fitness topic, there are a number of things to consider.


First, understand how small of a number 20% of your calorie burn actually is.

The average sized person who jogs for 30-45 minutes can expect to burn 200-300 calories from their workout.

If you did this fasted, in theory, you would burn up to 20% more calories.


20% of 200-300 calories is 40 to 60 calories.

That’s about the size of half of an apple.

While that’s something, from a sheer numbers perspective, it’s not going to move the fat loss needle in any significant way (at least for the average person).


Second, fasted cardio makes no sense if it means you will over consume calories later in the day.

You never want to view your calorie intake in an acute context.


It doesn’t matter how many calories you consume, or burn “in the moment”. What matters is your overall burn/consumption for the day.

If doing cardio fasted first thing in the morning leaves you ravenous later in the day, and you eat back those calories, the benefit is wiped out completely.


Not to mention the fact that the additional burn is a paltry amount; 40-60 calories is nothing, a handful of pretty much anything will put you over that many calories.


Third, your workout may suffer if you aren’t properly fueled for your cardio session.

Take 2 scenarios:  Fasted cardio versus fed cardio.


If doing your cardio fasted means your energy levels are lower, your intensity during your session may suffer.

A lowered amount of intensity could easily mean less calories burned, negating any benefit fasted cardio may give you.


You could also “putter out” on your cardio session more quickly, ultimately training for a shorter duration.

If eating a small breakfast and getting calories into your system means you can train harder, and for longer, it will likely be beneficial for you.


Should you do fasted cardio or not?

As with most fitness debates, the answer is less black and white than you think.


Technically, does fasted cardio burn more calories than fed cardio, if all else were equal?



Does that mean you should be doing fasted cardio instead of eating breakfast first?

It depends.


There are positives and negatives to this one.

Fasted cardio may burn a few more calories, but if eating before hand provides you with more energy, and less hunger later in the day, eating before your cardio is the better idea.


If you can maintain a high level of intensity during your cardio session, and stick to your diet regardless, there may be a slight benefit to doing your cardio fasted.

The real answer is quite simple; do as you prefer, and you can be consistent with.


If you love fasted cardio and it’s your preferred method – do it.

If you hate fasted cardio and you’d rather eat first – do it.


Ultimately, the type of activity you should do should reflect your preferences and what you enjoy.

That is easily the biggest key to staying active and healthy for life – no matter what the studies tell you.



Jason Helmes is a former Plymouth-Canton teacher who owns and operates Anyman Fitness out of his Canton home. Anyman Fitness is an online fitness coaching service that helps its clients reach their goals in a simple, straightforward manner. You can contact Jason at, or visit his site here for more information.

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