Is Fasted Cardio Better for Fat Loss?

What is Fasted Cardio?

Fasted cardio is a fancy term for doing cardio first thing in the morning on an empty stomach (coffee and water are fine). It is one of those “tried-and-true” methods for more rapid fat loss that has many people running to the elliptical in a state of zombie-like panic every morning, trying to be awake enough to function but not so awake that their stomach is screaming for breakfast, assuming that their efforts will lead to some extra pounds dropped on the scale.

For me, fasted cardio usually induces unpredictable cursing and broken phones (from smashing it up against a wall when the alarm goes off at an ungodly hour).

You know those pictures of someone doing cardio with a fishing line holding delicious food dangling in their face? This is the image I think of whenever I think about fasted cardio.

Wait I have that imagine somewhere…

There it is.

You can see where this is going, can’t you? It’s obvious that I am about to debunk fasted cardio. And if that’s all you needed to know, feel free to stop here and go eat some oatmeal.

Also, disclaimer: While I am about to debunk fasted cardio as a method to more rapidly drop fat, that doesn’t mean that fasted cardio is BAD. There’s absolutely nothing wrong with fasted cardio, if it’s what you enjoy. My mom, for example, prefers her morning runs on an empty stomach (save for a cup of coffee).

However, fasted cardio is not better than any other cardio-timing. As usual, it comes down to preference and likelihood of sustainability.

So Where Did This Fasted-Cardio Fad Come From?

In 1999, author and fit pro Bill Phillips wrote a book called Body-For-LIFE: 12 Weeks to Mental and Physical Strength. In it, he proposed the theory that performing cardio on an empty stomach is a more rapid and effective fat-loss approach. This method quickly became popular with body builders and physique athletes looking to lose as much fat as possible in a specific time frame. And I mean…it sounds pretty appealing, even to us gen-pop folk.

His rationale was that, in a fasted state, your body’s glycogen stores (the storage form of carbohydrates) are low. When this happens, there is less glucose circulating. Since your body prefers to use glucose for energy, and glucose is low, your body turns to stored body fat to fuel your workout.

And he’s right.

So…perfect recipe for maximized fat loss, right?

Not quite. And here’s why:

Your Body Doesn’t Operate in a Vacuum

We need to look at fat burning and energy usage over the course of days, not hours and minutes. For the most part, if your body burns more fat calories in one moment, it will burn more carbohydrate calories later on. And the reverse is true - if your body burns more carbohydrate calories in one moment, then later, it will burn more fat calories. Your body is smarter than you think - don’t try to trick it. As I said before, it prefers to use glucose for energy, and it will find a way to use the dang glucose whether it’s during your workout or later on. Unless of course you go full-on Keto. Which you probably shouldn’t do…but I’ll save that for another article.

Check out this study, in which there was no significant difference in body fat, waist circumference, or weight loss between two studied groups, one who cardioed in a fed state and one in a fasted state (both groups were eating in a caloric deficit): https://jissn.biomedcentral.com/articles/10.1186/s12970-014-0054-7

Also…

Fasted Cardio Has A Catabolic Effect on Muscle

Quite simply, what this means is that doing fasted cardio is more likely to cause breakdown of hard-earned muscle. This is because when glycogen stores are low, and you demand some intensity from your body (like during a workout), your body uses more than just fat for energy…it also uses an increased amount of amino acids (the building blocks of muscle).

Check out this study, in which subjects performed one-legged exercises, with one leg having low glycogen stores and the other higher glycogen stores (I read through the study to figure out exactly how they made this one-legged-glycogen-madness happen and I still don’t fully understand it…however the point remains): https://www.ncbi.nlm.nih.gov/pubmed/9831734

The study showed greater fat AND amino acid oxidation of the low-glycogen leg, which supports the knowledge that our body prefers to use glucose for energy and will turn to other sources (fat and muscle) when glucose is low.

Finally…

Fasted Cardio Impacts EPOC

EPOC (Excess Post-Exercise Oxygen Consumption) refers to the “after-burn” of intense exercise. EPOC is the oxygen consumption required to bring your body back to it’s stable, resting metabolic state, and it’s purpose is to help you create physiological adaptations that will help you recover from similar intensities of exercise in the future. The greater your EPOC, or post-exercise energy consumption, the higher your post-exercise calorie burn.

How to get a greater EPOC? Exercise more intensely. You can do this in two ways: doing a nice, long bout of moderate-high intensity exercise, like 50 minutes of cycling, or in 20 minute high-intensity intervals (HIIT). They literally burn about the same amount of calories and have a similar EPOC rate. (hint: chose HIIT)

But here’s the kicker: EPOC levels are much lower when exercising in a fasted state, regardless of the exercise intensity.

This means that no matter what exercise you do, you’ll likely burn less calories overall than if you did that same workout in a fed state.

Check out this study, where subjects completed a series of 4 exercise tests. The tests compared short duration/high intensity (think HIIT) and long duration/low intensity (think LISS, or a long run), both in a fed and a fasted state. Results showed a fairly significant increase in EPOC in a fed state, and even higher during the fed HIIT vs the fed LISS: https://www.researchgate.net/publication/261952856_High-intensity_interval_exercise_induces_24-h_energy_expenditure_similar_to_traditional_endurance_exercise_despite_reduced_time_commitment

So What Does This Mean For Me?

So is fasted cardio better for weight loss?

You’re in luck.

The “answer” is simple, as it usually is: No.

For the majority of the population, losing stored body fat comes down to the basic energy balance equation. Fasted cardio has no benefit over the same cardio done at any other time, when daily caloric balance is matched. This means that as long as you are eating slightly less calories than you are burning every day, you will lose body fat. It doesn’t matter when (or IF) you do your cardio.

Bottom Line: Do cardio when and how you want to. We know that moving your body is healthy for your joints, muscles, heart, and overall health and wellness, but “cardio” doesn’t have to be structured if you don’t want it to be. Your cardio can be 30 minutes on an elliptical on an empty stomach or an evening walk with your family after dinner. It can be a walking break at work every 25 minutes and consistently using the stairs instead of an elevator, or riding your bike to work. It can be marathon training or two sessions of HIIT per week. As long as you move your body often and eat a little less than you burn daily, you will lose body fat.

And as always, remember the rule of moderation. There are so many hypes and fads out there, but 100% of the time it will always come down to personal sustainability and consistency. If you can stick with it, and it adds to your life, it will work.

Love and sunshine, friends!