Written by Michael Matthews and Scientifically Reviewed by Dr. Brian Grant

Fact Checked Evidence Based

“Doing Cardio on an Empty Stomach Burns More Fat”

That’s the headline splashed across this month’s edition of a popular women’s fitness magazine.

Right next to it sits a popular men’s bodybuilding magazine with the following headline:

“Fat Loss Myth Busted: Cardio on Empty Stomach”

I flipped through both articles and, ironically, both had it wrong.

Doing cardio on an empty stomach doesn’t necessarily help you lose fat faster.

Doing fasted cardio can help you lose fat–and “stubborn” fat in particular–faster, though.

(And it works especially well when combined with several other fat loss strategies, which we’ll talk more about in this article.)

This sword cuts both ways, though.

Do your fasted cardio wrong and you won’t lose fat faster. You’ll just lose muscle instead, which is a good way to wind up skinny fat.

We’re going to break it all down in this article and learn the simple science of fasted cardio, including…

What fasted cardio actually is (and isn’t).

How it can help you lose fat faster.

Why it can cause muscle loss.

How to maximize its benefits (fat burning) and minimize its drawbacks (catabolism).

What types of fasted cardio are best.

And more.

By the end, you’ll know how to use fasted cardio to speed up fat loss without sacrificing muscle.

So let’s go. 🙂

Would you rather listen to this article? Click the play button below! Want to listen to more stuff like this? Check out my podcast!

My Fasted Cardio Results

I’ve gotten lean both with and without using the fasted cardio strategies I’m going to outline in this article.

And I can say that it’s noticeably faster with them.

You’ll learn why this is soon, but here’s an example of my personal results doing what I teach in this article:

BEFORE

I started this cut around 198 pounds and 11% body fat (I’m 6’2 in case you’re wondering).

I practice what I preach for about 10 weeks and…

AFTER

…got to about 185 pounds and 7% body fat.

And better yet, I did it without losing any muscle to speak of.

So, just know that while we’re going to review quite a bit of scientific research, I also have practical experience.

I know firsthand what it takes to get lean without drugs and without burning up all your muscle.

And fasted cardio has become an important part of my overall fat loss routine.

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What is Fasted Cardio?

Most people equate “cardio on an empty stomach” with “fasted cardio.”

They’re wrong.

Your stomach is empty when you do fasted cardio but not all cardio on an empty stomach qualifies as fasted cardio.

Quick…say it three times out loud!

Let’s break that statement down so it makes some sense.

First, the proper definition of fasted cardio:

Fasted cardio is cardio done in a fasted state.

Simple enough. So what’s a fasted state?

Well, to understand that, we have to review what happens in your body when you eat food.

When you eat a meal, your body digests and breaks the food down into various molecules like amino acids, glucose, and fatty acids.

The small intestine absorbs these nutrients into the blood, where they’re met by the hormone insulin.

Insulin’s job is to shuttle these nutrients into your cells for use.

How long this takes–and how long insulin levels remain elevated–depends on the composition and size of the meal.

When your body is processing the food you’ve eaten, you’re in a “fed” or “postprandial” state (prandial means “having to do with a meal.”)

When you’re in a fed state, insulin levels are higher than normal.

Once your body has completed the job, it enters a “fasted” or “postabsorptive” state.

When you’re in a fasted state, insulin levels are at a low, baseline level.

As you can see, your body moves in and out of these states every day.

And as you’ve probably already concluded, this goes beyond how “empty” your stomach feels.

Many people will feel “empty” an hour after eating but won’t be in a fasted state for another two or three hours.

That’s why you want to think “fed or fasted,” not “full or empty.”

So, to relate this back to cardio:

Cardio done when your body is still processing food and insulin levels are high is “fed cardio.”

Cardio done when your body is no longer processing food and insulin levels are at a low, baseline level is “fasted cardio.”

Now that we have some basic definitions under our belts, let’s look at what all this has to do with fat loss.

Fasted Cardio and Fat Loss: The Good and the Bad

Many people turn to fasted cardio (or what they believe is fasted cardio) because it sounds simple.

You don’t have to do any more exercise or cut any more calories or take any supplements.

You just change the time you exercise and, you hope, lose fat faster.

Well, it’s not that simple.

Fasted cardio nor any other type of exercise can speed up fat loss if you don’t also know what you’re doing with your diet.

The laws of energy balance are immutable.

At the end of the day, regardless of your workouts, fat loss requires an energy (calorie) deficit.

And that means you need to know how much energy you’re burning versus how much you’re eating.

The following tool can help you calculate this:

The Legion Macronutrient Calculator What unit would you like to use? Imperial (lb) Metric (kg) What's your gender? Male Female How much do you weigh? (in lb ) How tall are you? (in ft/in ) How old are you? (in years ) How much do you work out per week? None (little to no physical activity) A little (one to three hours of exercise or sports per week) A moderate amount (four to six hours of exercise or sports per week) A lot (seven to nine hours of exercise or sports per week) A TON (ten or more hours of exercise or sports per week) Custom Activity Multiplier ▲ ▼ Do you want to . . . Lose fat ("cut") Build lean muscle ("lean bulk") Maintain the same weight ("maintain") Your basal metabolic rate (BMR) is . . . Your total daily energy expenditure (TDEE) is . . . To lose weight , you should consume the following calories and macronutrients every day: Calories Protein 0 kcal Carbs 0 kcal Fat 0 kcal

There’s nothing wrong with “fed” cardio.

Any exercise burns energy and this helps you lose weight regardless of whether insulin levels are high or low.

If fasted cardio doesn’t fit your schedule or lifestyle or if you simply just don’t like it (some people don’t), don’t sweat it.

You can still reach your goals.

That said, fasted cardio has some unique fat loss benefits.

Research shows that exercising in a fasted state increases both lipolysis and fat oxidation rates.

Lipolysis is the breaking down of fat cells for energy.

Fat oxidation is the burning of this energy by cells.

So, what this research shows is that when you exercise with your insulin at a baseline level, your body is able to both mobilize and burn more fat during your workouts than when insulin levels are elevated.

Studies also show that blood flow in the abdominal region is increased when you’re in a fasted state.

This is important because one of the problems with the “stubborn fat” in this region is reduced blood flow.

Less blood flow means less fat-burning chemicals and thus less fat loss in the region.

Well, fasted training can help overcome this.

And especially when combined with proper supplementation, but we’ll talk more about that in a minute.

So that’s the good. What about the bad?

Well, there is a downside to fasted training:

It increases muscle breakdown rates.

The effects aren’t catastrophic but considering how hard it is to gain muscle naturally, it’s enough to matter.

And in case you’re not sure why this is undesirable, it’s simple.

If you damage and break down too many muscle cells in your workouts, your body won’t be able to keep up with repair.

That means less muscle growth over time or even muscle loss.

Another downside to fasted exercise is lackluster workouts.

Many people find they have less energy and focus when training in a fasted state.

This means lower levels of physical and mental intensity they’re used to.

So, as you can see, fasted training is a double-edged sword.

It’s good for losing fat faster, but it’s not so good for maintaining muscle and enjoying your workouts.

What About Fasted Weightlifting?

Fasted weightlifting is equally as effective as fasted cardio because it too dramatically spikes your body’s production of fat-burning chemicals.

When I’m cutting, I do all weightlifting and cardio workouts fasted.

A caveat, though:

When you switch from fed to fasted training, you’ll probably be weaker for the first few weeks at least.

I lose a few reps on my big lifts and sometimes one or two on my smaller exercises as well.

The point is don’t panic–this is normal.

It’s not because you’re losing muscle; it’s because eating a good amount of carbohydrate before you work out improves your performance.

Take the carbs away and you lose the “boost.” Put them back and you get it back.

That said, research shows that your body can adapt to training in a fasted state by “learning” to use its glycogen stores more efficiently.

Even so, I’ve found that my lifts in fasted workouts are just never as good as fed ones.

2 Ways to Burn More Fat With Fasted Cardio

Fasted cardio is often criticized by educated fitness folk for having little practical value.

They don’t argue the physiological realities we discussed earlier but they say that it doesn’t pan out to much in actual practice.

They have a point.

Research shows that by itself, fasted cardio doesn’t burn all that much more fat.

When you combine fasted cardio with high-intensity interval training (HIIT) and a few supplements, though, the effects are much more pronounced.

And they become especially noticeable when you’re in the later stages of a cut , with the a fair amount of stubborn fat left to lose.

Let’s take a look at why.

1. Do Fasted HIIT Cardio

High-intensity interval training is an exercise method that alternates between periods of (almost) all-out intensity and low-intensity recovery.

The idea is simple:

During your high-intensity bouts, you’re pushing yourself almost as hard as you can.

During your low-intensity periods, you’re trying to catch your breath in preparation for the next sprint.

And why should you subject yourself to this, you wonder?

Two reasons.

You lose fat faster with HIIT cardio.

An abundance of research shows that high-intensity interval training is more time effective for losing fat than traditional “low-intensity steady-state” cardio (LISS).

For example, this study conducted by researchers at the University of Western Ontario found that people lost more fat doing 4 to 6 30-second sprints (with 4-minute rest periods) than 60 minutes of incline treadmill walking.

If you do the math here, that’s pretty impressive.

17 to 27 minutes of high-intensity interval training resulted in more fat loss than 60 minutes of traditional bodybuilder cardio.

This wasn’t a one-off occurrence, either–these types of results are seen in quite a few other studies as well.

The science is clear: if your goal is to burn as much fat in as little time as possible, then HIIT is the way to go.

Although the exact mechanisms behind this aren’t fully understood yet, scientists have isolated several factors.

Research shows that HIIT…

Increases your metabolic rate for up to 24 hours.

Improves insulin sensitivity in the muscles. This helps your body better absorb and use the food you eat (rather than store it as fat).

Increases your muscles’ ability to burn fat for energy.

Elevates growth hormone levels, which aids in fat loss.

Spikes catecholamine levels, which are chemicals that mobilize fat for burning.

Decreases post-exercise appetite, which helps prevent overeating.

The bottom line is if you want to get as much fast loss bang for your cardio buck, you want to do HIIT.

And when you do it in a fasted state it’s even more effective because physiological mechanisms related to fat loss work better in a low-insulin environment.

You lose less muscle too.

When you’re dieting for fat loss, your number one goal after, well, losing fat, is preserving muscle.

And when it comes to muscle preservation, steady-state cardio has a pretty bad rap.

There are valid reasons for this.

For example, research shows that the longer your cardio sessions are, the more they impair strength and muscle growth.

That doesn’t mean you have to fear cardio, though.

There are four simple steps you can take to maximize fat loss and minimize muscle loss:

The reasoning behind point #4 is this:

When you’re in a calorie deficit, the less cardio you do, the more muscle you’ll preserve.

That’s a bit simplistic but it works as a rule of thumb.

Now, you can do no cardio whatsoever and lose fat, of course, but this will only get you so far.

If you want to get really lean (sub-10% for men and sub-20% for women), there’s a point where you have to include cardio in your routine.

You need it to keep energy expenditure high enough to continue losing fat.

Thus, the predicament:

You need to use cardio to bolster your daily energy expenditure and fat loss but you also need to keep it to a minimum to preserve muscle.

How do you go about this?

Well, what you don’t do is follow the example of many people an turn to the Dark Side:

Hours and hours of grueling cardio every week to burn both fat and muscle away.

Combine this with very-low calorie dieting, which is all too common as well, and you have a perfect storm of misery and muscle loss.

Well, you can have the best of both worlds with high-intensity interval training.

You don’t need to do more than a couple hours per week to noticeably increase fat loss…and each session only needs to be 20 to 30 minutes.

How to Do HIIT Correctly

You’re chomping at the bit to incorporate HIIT into your fat loss routine?

Great.

You probably have a few questions, though, such as…

How “intense” do the high-intensity intervals need to be?

How “restful” and long should the rest periods be?

How long should the workouts be?

How frequently should you do HIIT workouts?

Basically…

What actually qualifies as a HIIT workout and how do you get the most out of this type of training?

Well, this article breaks it all down.

Homework! 🙂

2. Supplements That Make Fasted Cardio More Effective

Supplements aren’t the key to fat loss, but if you combine the right ones with a proper diet and exercise routine, you can speed up the process.

Here is my personal “fat loss stack” that I use and recommend:

Caffeine

Millions of people can’t shake the cobwebs without their morning cups of coffee but this powerful compound has a lot more going for it.

Caffeine helps you lose weight by increasing the amount of energy your body burns throughout the day, and it also improves strength, promotes muscle endurance, and enhances anaerobic performance.

For best results, research has shown that caffeine is best delivered in a pill or powder format, though you must be careful to avoid building up a tolerance to it.

Personally I get my caffeine from my pre-workout PULSE, which also contains clinically effective dosages of 5 other ingredients scientifically proven to improve workout performance:

HMB

As you know, the main drawback to fasted cardio is muscle loss.

The most common solution for this is branched-chain amino acid supplement (BCAAS).

BCAAs can get the job done but a better choice is a fancy-sounding molecule called β-Hydroxy β-Methylbutyrate (HMB).

HMB is a substance formed when your body metabolizes leucine, which is an amino acid that stimulates protein synthesis.

HMB is often sold as a muscle-building aid but the research purported to demonstrate these benefits is shaky at best, hindered most by design flaws. Thus, I’m not comfortable making any claims about muscle growth.

There is one benefit of HMB that’s well established, however: it’s an extremely effective anti-catabolic agent.

That is, it’s very good at preventing muscle breakdown, which means you will recover faster from your workouts and experience less muscle soreness (and the free acid form shows the most promise in this regard).

It also has no effect whatsoever on insulin levels, which means it won’t break your fasted state like food.

These things make HMB perfect for use with fasted training.

Its powerful anti-catabolic effects and non-existent insulin effects means you reap all the fat loss benefits of training fasted without any of the problems relating to muscle loss or insulin secretion.

It’s also worth noting that HMB is superior to leucine in suppressing muscle breakdown because it’s more anti-catabolic than its “parent” amino acid.

This means it’s also more effective than branched-chain amino acid (BCAA) supplements because they rely on leucine for their anti-catabolic effects (isoleucine and valine are very weak in this regard).

Clinically effective dosages of HMB range between 2 and 3 grams, and that’s what you’ll find in my pre-workout fat burner FORGE:

Yohimbine

Yohimbine is a chemical extracted from a species of African plant, Yohimbe.

Studies show that yohimbine can accelerate fat loss by blocking the activity of alpha-receptors in fat cells.

This enables your body to reduce fat stores faster and is particularly useful as you get leaner and are battling with stubborn fat holdouts.

There’s a slight catch with yohimbine, though: elevated insulin levels negate its weight-loss effects. If you want to reap its fat loss benefits, you want to use it when you’re in a fasted state.

Yohimbine’s benefits don’t stop there, though. It does more than help you lose fat faster.

Research shows that yohimbine also improves exercise performance, and it’s particularly effective at fighting off physical fatigue and increasing time to exhaustion.

These are the reasons why I decided to include yohimbine in my pre-workout fat burner FORGE, which was made specifically for maximizing fat loss with fasted training.

PHOENIX Fat Burner

PHOENIX’s caffeine-free formulation helps you burn fat in three different ways:

It dramatically increases metabolic speed

It amplifies the power of fat-burning chemicals produced by your body

It increases the feeling of fullness from food

Many companies try to sell you their fat burners by making the process of fat loss sound overly complex.

They talk about increasing fat oxidation rates, preserving lean mass, supporting the thyroid, inducing thermogenesis, inhibiting enzymes related to fat storage, inducing enzymes that cause fat loss, manipulating hormone and neurotransmitter levels, reducing water retention, improving nutrient partitioning, and more.

Well, the truth is these are all aspects of fat loss, but this type of marketing is little more than an attempt to dazzle you with terminology and scientific half-truths in hopes that you just accept the claimed benefits at face value.

When you take a cold, hard look at the science of fat loss, there are really only three ways to appreciably speed it up:

1. You can increase your basal metabolic rate.

Your metabolic rate is a “count” of how much energy your body burns throughout the day, and the higher it goes, the faster you can lose weight.

This is because when you boil fat loss down to its utmost simplicity, it’s determined by the difference between the energy your body burns and the energy you feed it with food. Expend more energy than you consume over time, and you’ll lose fat.

While there are many, many ways to increase metabolic rate, they ultimately rely on one or both of the following mechanisms:

Encourage a cell to produce more energy from carbohydrates and fatty acids. Reduce the efficiency of the process through which cellular energy is produced, thus increasing the “energy cost” of meeting the body’s needs.

There are many ways to manipulate those mechanisms and PHOENIX focuses on the most effective methods.

2. You can prevent hunger or cravings from ruining your plans.

A major reason diets fail is people just aren’t able to stick to them long enough. Wishes turn into cravings and ultimately binges, which can undo days or even weeks of hard work if it really gets out of hand.

While some people have an easier time than others, almost everyone has to deal with hunger and cravings to one degree or another. It’s just human nature to want to indulge in food after accidental or intentional deprivation, and whether it’s normal or not, it’s still interfering with your goals.

Many compounds are known to reduce hunger and others are known to increase the sensation of fullness you get from a meal. When a combination of proven molecules is used effectively, you can successfully reduce hunger and cravings and derive the maximum benefits from your diet.

3. You can make the overall experience of dieting more enjoyable.

Make no mistake: while recreating your body with smart diet, exercise, and supplementation can dramatically change your life for the better, it’s not easy.

No amount of pills or powders are going to get you there. It takes hard work, and it takes time. And this is another major reason why diets fail: people don’t want to go through the discomfort of it all.

Well, like reducing hunger and cravings, making the process of dieting more enjoyable, primarily by increasing the overall feeling of well-being, makes it easy to stick to the plan and see it through.

Although the molecular machinery of fat loss is vast and complex, the practical application remains simple.

Contrary to what many other companies would lead you to believe, directly stimulating any of the thousands of proteins and enzymes involved in fat loss either doesn’t work or is uninvestigated.

Fat loss is a whole-body process, and by focusing on simple, key, and proven targets everything else activates and functions accordingly.

PHOENIX’s formulation is the result of an extensive scientific review of a wide variety of natural molecules known to favorably affect fat loss, and we carefully chose a handful that work synergistically to safely deliver consistent results on all three points given above.

Is Fasted Cardio in the Morning Best?

This is a common question, especially among intermittent fasters.

And the answer is simple.

The benefit of doing fasted cardio first thing in the morning is it ensures your insulin is at a true baseline level.

This is why research shows that fat oxidation rates are highest after 6+ hours of fasting.

And this is why many people that do fasted cardio do it after waking and before eating.

It works well.

Don’t think you have to do fasted cardio first thing in the morning to reap its benefits, though.

You can ensure you’re in a fasted state later in the day but you have to plan your meals accordingly.

For example, just 35 grams of sugar is enough to raise insulin levels above baseline for a few hours.

In this study, a mixed meal of 75 grams of carbs, 37 grams of protein, and 17 grams of fat elevated insulin levels for over 5 hours.

Hell, even a serving of whey protein takes a couple hours to fully process.

So, what this means is you can’t eat a large lunch and expect to be in a fasted state by 5 PM.

Here’s how I do it:

I do a fasted weightlifting workout first thing in the morning, before eating.

I have a couple scoops of whey protein after.

I have a light lunch of a salad with about 6 ounces of chicken.

I have another scoop of whey protein around 3 PM.

I do my cardio around 6 PM.

I eat a large dinner afterward.

I eat another large meal around 9 PM.

As you can see, my calories and carb intake are low until dinner. This ensures my insulin levels remain low as well.

And, as a note, if my 3 PM meal were larger (if it contained a sizable amount of carbohydrate, for example), I wouldn’t be fasted by 6 PM.

But 3 hours is enough time to process a meal of only 20 to 25 grams of whey protein.

Should You Eat After Fasted Cardio?

If we’re talking just fat burning, continuing the fast after exercising would seem to make sense.

The fat-burning chemicals your body produced during the workout are still in your blood (and so are the ones you added through supplementation).

The problem, however, is muscle degradation ramps up after fasted exercise if you don’t eat.

And stopping that takes precedence over wringing out every possible gram of fat loss.

Some people get “fancy” and choose to take another serving of HMB or BCAAs after training to extend the fast for another hour or two.

This is an option, I guess, but I don’t think it makes much sense for two reasons:

1. Catecholamine levels return to normal shortly after you stop exercising.

This begs the question of how much additional fat are you really burning by waiting to eat?

2. It’s expensive.

If you’re taking serving of HMB or BCAAs before and after fasted training…and if you’re doing several fasted workouts per week…it’s going to hurt your wallet.

That’s why I just break the fast after training and eat a high-protein meal.

I would make it a high-carb meal as well but these days I’m enjoying getting the majority of my carbs at night.

My Fasted Cardio Routine

Before we wrap up, I want to share with you a simple “do this to lose fat faster” routine that has served me and thousands of people I’ve worked with well.

It starts with a 25% calorie deficit and a high-protein diet, and 4 to 5 hours of heavy weightlifting and 1.5 to 2 hours of HIIT cardio per week.

Remember that no amount of supplementation will matter if you don’t get your diet right.

Once you do, though, supplementation can help. And here’s how my routine breaks down:

Before Weightlifting (Fasted):

About 15 minutes before my fasted weightlifting session, which I do first thing in the morning (about 45 minutes after waking), I take the following:

1 serving of FORGE 1 serving of PHOENIX 1 scoop of PULSE

My weightlifting session lasts about 45 to 60 minutes and afterward I eat my first meal of the week, which contains about 50 grams of protein.

With Lunch:

I eat a light lunch of a salad with chicken and a scoop of whey protein a couple hours later so I can be back in a fasted state by 5:30 PM, which is when I do my fasted cardio.

I don’t take any fat loss supplements at lunch.

(It’s worth noting that I also have a scoop of whey at about 3 PM, which gives my body about 2.5 to 3 hours to process it before cardio.)

Around 5:30 PM, Before Cardio

About 15 minutes before doing my fasted cardio, I take the following:

1 serving of FORGE 1 serving of PHOENIX 1 scoop of PULSE

I then do 25 minutes of HIIT cardio on the upright or recumbent bike and eat dinner after.

The Bottom Line on Fasted Cardio (and Weightlifting)

Fasted training isn’t a magic bullet but, if you follow my advice in this article, it will help you lose fat faster while preserving your muscle.

This is especially true when you’re struggling to lose that lower ab fat (guys) or hip, thigh, and butt fat (girls).

If, however, fasted cardio doesn’t work out for you for whatever reason, don’t worry.

You can get the same results with exercising in a fed state. It might just take a little bit longer to shrink the “stubborn” areas of your body (and here’s why).

What’s your take on fasted cardio? Have anything else to share? Let me know in the comments below!