Fasted Cardio: Benefits, What It Is & How to Lose Weight

Browse through the blogosphere or flip through a few fitness magazines, and you’d think that the benefits of fasted cardio were a gift from the fat-burning gods.

At this point, the idea that fasted cardio is better for burning fat than regular, fed cardio has become axiomatic. Of course it’s better for fat loss say the magazines, personal trainers, and fitness gurus.

And according to some people, it’s particularly helpful for burning away the “stubborn” fat covering the stomach and lower back on men and the butt, thighs, and hips of women.

Of course, there are also naysayers.

Some people claim the benefits of fasted cardio are oversold and that it’s no better for fat loss than fed cardio. Others even claim that it accelerates muscle loss and makes your workouts harder, thus making it more difficult to improve your body composition.

Who’s right?

You’ll learn the answer in this article. You’ll learn the answers to all of the following questions:

What is fasted cardio?
What are the benefits of fasted cardio?
How do you use fasted cardio to lose fat (and in particular “stubborn fat”) fast?
How do you do fasted weightlifting?

What Is Fasted Cardio?
Benefits of Fasted Cardio
Does Fasted Cardio Help You Lose Fat Faster?
How Fasted Cardio Can Help You Lose “Stubborn” Fat
What About Fasted Weightlifting?
FAQ #1: How long should you do fasted cardio?
FAQ #2: Can I drink coffee before fasted cardio?
FAQ #3: How long should you wait to eat after fasted cardio?
FAQ #4: What should I eat after cardio to lose fat?
FAQ #5: Should I do fasted cardio in the morning?

What Is Fasted Cardio?

Fasted cardio is any cardio exercise done while in a “fasted” state.

“Fasted,” in this sense, doesn’t just mean “hungry” or having an empty stomach—it has to do with how your body processes and absorbs the food you eat.

When you eat food, it gets broken down into various molecules that are released into your blood and used by your body. The hormone insulin is released as well, and its job is to shuttle these molecules into cells.

When your body is digesting and absorbing what you’ve eaten, and insulin levels are still high, your body is in a fed or postprandial state (prandial means having to do with a meal).

Once your body is finished processing and absorbing the nutrients, insulin levels drop to a minimum (baseline) level, and your body enters a fasted or postabsorptive state.

How long it takes for insulin levels to fall back to baseline depends on the size and composition of your meal.

Larger meals (like a slice or two of pizza) that include a mix of protein, carbs, fat, and fiber digest slowly—normally over the course of five or more hours. During this time your insulin levels will remain elevated.

On the other hand, if you eat a smaller, simpler meal (like a single scoop of whey protein isolate), your insulin levels will fall back to baseline within a few hours. Carbs have a similar effect, with 35 grams of sugar being enough to raise insulin levels above baseline for a few hours.

Your body moves in and out of these fed and fasted states several times a day. Thus, for your cardio workouts to be truly fasted, you need to time them properly so they occur in a postabsorptive (fasted) state.

Benefits of Fasted Cardio

The benefits of fasted workouts have been extolled since the late 90s, when Bill Phillips, a former competitive bodybuilder and founder of Body for Life, recommended exercising before breakfast as a way to burn fat more efficiently.

He claimed that working out before you’d eaten would force the body to burn its fat stores for energy, since it wouldn’t have any food to digest instead.

Since then, the language used to describe these fasted workout benefits has changed somewhat. Ask anyone in the evidence-based fitness community these days what the benefits of fasted cardio are, and they’ll tell you all about how it increases both lipolysis (the break up of fat cells) and fat oxidation (actual fat burning) rates.

Regardless of which way you spin it, though, the message is the same: the benefit of working out fasted is that you break down and burn more fat cells for energy than you would if you had eaten prior to exercising.

Does Fasted Cardio Help You Lose Fat Faster?

The reason people believe fasted cardio increases fat loss has to do with insulin.

Insulin does more than just shuttle nutrients into cells—it also impairs the breakdown of fatty acids. That is, the higher your insulin levels are, the less fat your body is going to use for energy.

This makes sense physiologically. Why would your body burn fat when there’s a surplus of energy readily available via the food you just ate?

Thus, when you eat food, your body shuts down its fat-burning mechanisms and lives off the energy provided by the meal. Any excess energy it doesn’t use is stored as body fat for later use.

As your body processes and absorbs the food, insulin levels decline, which tells the body to start burning body fat for energy as the “fuel” from the meal is running out.

Finally, when the absorption is complete, your body is running almost entirely off its own body fat stores for energy.

Here’s a simple graph that shows this visually:

The rationale for fasted cardio is that by doing your workouts in a fasted state—when your body is running mostly on body fat—you can burn more total body fat than if you did the same workouts in a fed state.

But does this play out in reality?

Fasted Cardio and Fat Burning

A wealth of research shows that training in a fasted state increases fat oxidation.

That is, doing cardio in a fasted state increases the amount of body fat that’s burned for energy.

That said, that the number of calories you burn during a workout is just a fraction of your total daily energy expenditure (TDEE), which is what really determines how much fat you lose over time (assuming you’re eating a consistent number of calories). What’s more, when you burn more fat during a workout, you just burn less later in the day.

The real question, then, is does the small increase in fat burning during fasted cardio translate into a significant boost in fat loss over the course of the entire day?

Probably not.

A good example of this comes from a study conducted by scientists at the University of Padua which found that . . .

Participants who fasted before running burned more fat and less carbs during the workout, but burned more carbs and less fat during the rest of the day.
Participants who ate before running burned more carbs and less fat during the workout and more fat and less carbs during the rest of the day.

All in all, the researchers found that both groups burned the same amount of carbs and fat by the end of the day. Fasted cardio didn’t help them burn any more fat than fed cardio. Another study conducted by scientists at Lehman College found similar results.

The reason for this is that during exercise, the body uses nutrients for energy in a specific order:

Blood glucose
Stored carbohydrate (muscle glycogen)
Stored body fat
Stored body protein (muscle).

When carbohydrates are readily available, the body prefers to burn them over body fat, and when carbs are scarce, it prefers to rely more on body fat stores for energy.

In other words, the body compensates for an increase in fat burning during fasted cardio with a decrease in fat burning during the rest of the day.

Another downside to fasted cardio is that while it does result in more fat burning during exercise, much of the fat isn’t the subcutaneous stuff that wiggles and jiggles when you walk. Instead, about half comes from fat stored in your muscle cells (known as intramuscular triglycerides).

To make matters worse, the fitter you become, the more your body will tap into these muscle fat stores instead of burning the body fat you want to get rid of (like the stuff covering your abs).

On the whole, then, fasted cardio doesn’t increase fat burning in and of itself. That said, it can still be useful when combined with the right supplements (more on this in a moment).

Fasted Cardio and Calorie Burning

Fasted cardio doesn’t help you burn more calories than fed cardio.

This was proven in a study conducted by scientists at the University of Tsukuba in Japan. The scientists had 12 young male endurance athletes report to the lab and undergo both of the following protocols with one week between each:

One hour of easy indoor cycling after eating breakfast (fed cardio)
One hour of the same exercise protocol before eating breakfast (fasted cardio)

The researchers kept all of the subjects locked in the lab for three days so they could carefully measure their food intake, energy expenditure, and fat loss. They found zero difference in 24-hour energy expenditure between the groups.

The bottom line is that fasted cardio—by itself—won’t help you lose fat faster than regular fed cardio. When you combine it with the right supplements, though, then it can help you get rid of “stubborn” fat faster.

How Fasted Cardio Can Help You Lose “Stubborn” Fat

If you’re a woman, your hips, thighs, and butt are probably the last to really tighten up when you’re losing weight.

If you’re a guy, it’s almost certainly your lower abs, love handles, and lower back.

This isn’t a genetic curse—it’s simply a physiological mechanism your body uses to defend against extremely low body fat levels. And fasted cardio can help you overcome it.

Let’s start with a physiological explanation of the stubborn fat phenomenon.

Your body uses chemicals known as catecholamines to trigger fat burning. Catecholamines travel through your blood and attach to receptors on fat cells, which then trigger the release of the energy stored within the cells for use.

Fat cells have two types of receptors for catecholamines: alpha- and beta-receptors. To keep this simple, beta-receptors speed up fat mobilization, whereas alpha receptors hinder it.

The more alpha-receptors a fat cell has, the more resistant it is to being mobilized by catecholamines. On the other hand, the more beta-receptors a fat cell has, the more receptive it is to these fat-mobilizing molecules.

As you’ve probably guessed, the areas that get lean quickly have a lot of fat cells with more beta-receptors than alpha, and the areas that don’t have a large amount of fat cells with more alpha-receptors than beta.

Another problem with these stubborn fat deposits relates to blood flow.

You may have noticed that fat in areas like the lower back and thighs are slightly colder to the touch than fat in other areas of your body like the arms or chest. This is simply because there’s less blood flowing through the areas.

Less blood flow = fewer catecholamines reach the stubborn fat cells = even slower fat loss.

So we have a double-whammy of fat loss hindrance here: large amounts of fat cells that don’t respond well to catecholamines and reduced blood flow that keeps the catecholamines away.

This is why you can lose fat and weight steadily with almost all of the fat seeming to come from everywhere but your “problem” areas.

Fasted cardio helps in this regard because blood flow in the abdominal region is increased when you’re in a fasted state, which means the catecholamines can reach this stubborn fat easier, hypothetically resulting in greater stubborn fat mobilization.

This means that while fasted cardio won’t help you lose more total fat every day, it probably will help you lose more of the fat you want to lose most.

It’s worth noting that no studies have proven this to be the case, but there’s a strong theoretical argument that it works.

And this is especially true if you combine fasted cardio with a supplement called yohimbine.

Fasted Cardio and Yohimbine

Yohimbine is a supplement made from the Pausinystalia yohimbe plant, and several studies have shown that it can speed up fat loss.

It does this by stimulating the production of catecholamines, which speeds up your basal metabolic rate and suppresses your appetite.

In one study conducted by scientists at the Université Paul Sabatier, researchers found that twice as much fat was mobilized (drawn out of fat cells) when participants took yohimbine after an overnight fast compared to when they took it after eating breakfast.

The same scientists also carried out another experiment in the same study. In it, they found that when participants took yohimbine and did 30 minutes if moderate-intensity exercise, fat mobilization increased by more than 150% above baseline.

Yohimbine’s fat-burning effects don’t stop there: it can also help your body better tap into and burn stubborn fat stores.

It accomplishes this by attaching itself to and interfering with the alpha receptors on fat cells, which, we recall, are the ones that gobble up catecholamines and shut down fat mobilization.

Thus, if enough alpha receptors are out of commission, it will be easier for catecholamines in your blood to bind to the beta receptors on fat cells instead, which stimulates fat loss.

This is why it’s considered particularly effective at helping you get rid of your alpha-receptor-laden, stubborn fat holdouts.

The reason I say “considered” is because research hasn’t definitively proven that yohimbine burns stubborn fat, but there is strong indirect evidence this is the case.

For instance, in a 3-week study conducted by scientists at the Institute of Sports Medicine in Serbia, a group of elite-level soccer players who supplemented with yohimbine lost five pounds of fat, while their teammates who took a placebo lost none.

That’s impressive, but here’s the kicker:

These athletes started around 9% body fat, which means much of the fat they had left to lose was the stubborn stuff in their lower torso.

That means there’s a good chance that most of the fat they lost during the experiment was belly fat, since it’s very unlikely any of these guys had pounds of intramuscular fat stores to burn.

All this is why I believe that if you want to lose stubborn fat as quickly as possible, it’s worth trying a combination of yohimbine and fasted cardio.

If you’re looking for a properly-dosed, all-natural yohimbine supplement, try Forge. It contains 10 mg of yohimbine HCL per serving along with three other ingredients to help maintain muscle mass, training intensity, and mental sharpness during fasted cardio.

What About Fasted Weightlifting?

Weightlifting causes a dramatic spike in plasma catecholamine levels and as catecholamines are better able to mobilize fat when you’re in a fasted state, fasted weightlifting is also worthwhile.

There is a major downside to fasted weightlifting, though: you’ll probably find you’re noticeably weaker during your first couple of weeks after switching from fed weightlifting to fasted.

This isn’t because you’re losing muscle. It’s simply because eating carbs before you work out improves your performance in the gym, and taking away those carbs decreases it.

Some people experience more of a decrease than others, which is why I recommend you try fasted weightlifting and see how your body responds.

If you don’t notice much of a decrease in performance, it might be worth doing your weightlifting workouts fasted to increase fat burning.

If you feel sluggish and weak and your strength plummets, it’s probably better to keep doing your weightlifting workouts fed.

FAQ #1: How long should you do fasted cardio?

Your fasted cardio sessions should last around 30-to-45 minutes each. Going much longer than this often feels fatiguing, especially when you’re in a large calorie deficit.

You can continue to do fasted cardio for as long as you’re in a cut. That said, if you start to feel frazzled during your fasted workouts, don’t feel like you have to keep training fasted. The benefits are fairly small, so it’s not worth compromising your workout quality just to train fasted.

FAQ #2: Can I drink coffee before fasted cardio?

Yes, as long as it’s plain, black coffee. That means no milk, cream, sugar, or syrup.

Drinking coffee before fasted cardio is actually a good idea.

This is because the caffeine in coffee increases the number of calories your body burns throughout the day.

What’s more, it increases strength, muscle endurance, and anaerobic performance, which means you can perform at your best in your workouts.

You can also get your caffeine from a pre-workout supplement, like Pulse, which contains 350 mg of caffeine per serving and clinically effective dosages of five other ingredients scientifically proven to improve workout performance. And if you don’t want all the caffeine, you can also take caffeine-free Pulse.

An ideal fasted cardio supplement stack would be something like a serving of caffeinated Pulse, a serving of Forge (which contains yohimbine), and a serving of Phoenix, our all-natural fat burner supplement.

FAQ #3: How long should you wait to eat after fasted cardio?

Try to eat something within 30 minutes of finishing your fasted workout, and make sure it contains at least 30 to 40 grams of protein.

This will minimize muscle protein breakdown and increase muscle protein synthesis.

Some people would disagree with that advice and say that you should wait another hour (or longer) before eating after a fasted workout to prolong the fat-burning effects.

This is unnecessary and counterproductive for two reasons:

1. You won’t lose more body fat.

Assuming your total calorie intake for the day is the same, you’re going to lose the same amount of body fat whether you have a meal before, right after, or several hours after your workouts.

Furthermore, most of the fat-burning benefits of fasted training occur during the exercise—not afterwards—which makes prolonging the fast unnecessary.

2. You’ll probably lose muscle.

Muscle protein breakdown drastically increases after both resistance training and cardio workouts.

This problem is only aggravated by fasted training, which increases breakdown rates even further.

And just to add insult to injury, most people use fasted training when they’re also in a calorie deficit, which also boosts muscle loss.

Thus, prolonging the fast after your workout is over increases your chances of muscle loss and doesn’t offer any additional fat-burning benefits, making it a poor choice when weighed in the balance.

FAQ #4: What should I eat after cardio to lose fat?

Whatever you like, just try to make sure it contains around 30 to 40 grams of protein.

You’ll find many meals that fit the bill in this article:

20 Post-Workout Meals That You Will Savor to the Last Bite

(And if you’d like even more specific advice about how many calories, how much of each macronutrient, and which foods you should eat to reach your health and fitness goals, take the Legion Diet Quiz.)

FAQ #5: Should I do fasted cardio in the morning?

Many people do fasted cardio first thing in the morning because it ensures your insulin is at its lowest level.

That doesn’t mean you have to, though.

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

Most large meals will elevate your insulin levels for at least 5 hours, and even a serving of whey protein takes ~2 to 3 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 p.m.

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 p.m.
I do my cardio around 6 p.m.
I eat a large dinner afterward.
I eat another large meal around 9 p.m.

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

Also note that if my 3 p.m. meal were larger (if it contained a sizable amount of carbohydrate, for example), I wouldn’t be fasted by 6 p.m. But 3 hours is enough time to process a meal of 20 to 25 grams of whey protein (about one scoop).