This is one of the ways I have changed my body so significantly. fasted-hiit-cardio

I never did this on purpose, but once I started researching it, I said to myself…“This is what I do!!”

Basically, I STOP EATING at 7pm. And I start my workout at about 5am.

So I must share it with you! 😉

Because I am not a scientist, or a personal trainer or nutritionist….I will leave it up to the experts to explain fully what Fasted Cardio is and WHY is works, HOW it works, and what you need to be mindful of when you are doing it.

Reprint from http://www.muscleforlife.com

Some people swear by fasted cardio whereas others say it’s not only ineffective but harmful as well. Well, both are right–it’s effective if you do it right and harmful if you do it wrong.

Like flexible dieting, fasted cardio has been around for quite some time and is now gaining popularity again as an effective way to accelerate fat loss.

And like most everything in the health and fitness space, it has its proponents and detractors. Proponents have their laundry list of reason why they like it and detractors have theirs as to why they don’t.

Well, I thought it time to weigh in on the matter because while I do have a good scientific understanding of the matter, I also have practical experience and know what it takes to get to 5 to 6% body fat without drugs and without burning up all your muscle. And fasted cardio has been an important part of my overall fat loss routine.

So, in this article we’re going to first review the science of fasted cardio, and then look at how to properly use it to make fat loss easier and faster. Let’s begin.

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What is Fasted Cardio?

what is fasted cardio

Many people think fasted cardio is simply training on an “empty stomach,” which they usually think is simply a stomach that “feels empty.”

Well, they’re wrong.

Fasted cardio is cardio done while in a “fasted” state, wherein your stomach is empty, but it’s a bit more than that. 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 your cells can use, and these molecules are released into your blood. Insulin is released as well, and its job is to shuttle these molecules into cells. Depending on how much food you eat in a meal, your insulin levels can remain elevated for several hours (anywhere from 3 – 6+).

When your body is digesting and absorbing what you’ve eaten, your body is in a “fed” or “postprandial” state (prandial means “having to do with a meal”). Once it has finished processing and absorbing the nutrients, insulin levels drop to a “minimum” low (or “baseline” level), and your body enters a “fasted” or “postabsorptive” state. Every day your body moves between “fed” and “fasted’ (or “postprandial” and “postabsorptive”) states.

So, to recap:

  • Exercise done during periods where insulin levels are elevated and food is still being processed and absorbed is “fed” training.
  • Exercise done during periods where insulin is at a low, baseline level and food is no longer being processed and absorbed is “fasted” training.

Alright, now we know what fasted cardio is. Let’s now look at how fed and fasted states relate to fat burning and storage.

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Your Body Doesn’t Burn Fat When It’s Fed–It Stores It

fasted cardio definition

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 your body is going to use fat for energy (both body fat and dietary fat).

This makes sense physiologically. Why burn fat when there’s a surplus of energy readily available via the food we just ate? Thus, when you eat food, your body basically shuts down its fat-burning mechanisms and lives off the energy provided by the meal, and it also stores a portion of the excess energy as body fat for later use.

As your body processes and absorbs the food, insulin levels decline, which tells the body to start going to fat for energy as the “fuel” from the meal is running out. Finally, when the absorption is complete, your body is fully running off its own fat stores for energy.

Here’s a simple graph from Weightology that shows this visually:

insulin-facts

As you can see, if the amount of fat stored and fat lost remains balanced over time, our weight doesn’t change. If we burn more fat than we store, we lose weight. And if we store more fat than we burn, we gain weight.

So, that’s how “fed” and “fasted” states work without considering exercise. What happens when we throw that into the mix?

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The Science of Fasted Cardio and Weight Loss

fasted hiit cardio

Fasted cardio is often recommended as a way to speed up fat loss, but usually without an in-depth explanation of how this might actually work, and how it fits into the bigger picture of weight loss.

Hence my “inspiration” for this article, because just telling someone to train fasted with no other advice almost certainly won’t make a difference in terms of losing weight.

The first thing you should know about fasted cardio is it won’t help you lose fat faster if you don’t also follow a proper diet.

Fasted cardio does not let you somehow cheat the laws of energy balance. At the end of the day, fat loss requires an energy (or calorie) deficit, and that means you have to burn more energy than you eat.

That said, fasted cardio does offer some unique fat loss benefits when done properly. Let me explain.

As you would expect, if your insulin levels are elevated before exercise due to a pre-workout meal, your body will break down less fat cells during that workout (lipolysis will be blunted). Research has proven this true both with trained and untrained individuals.

That said, lipolysis is only one part of fat loss. The other part is fat oxidation, which is the actual use (“burning”) of the fatty acids by cells.

Your body could break down every fat cell it has into usable fatty acids, but most would go unused (your body only burns so much energy) and wind up reconverted back into body fat.

And this is where some people criticize fasted cardio as worthless. They say that while it’s true that exercising in a fed state means less lipolysis during the workout, fat oxidation rates aren’t affected so all that happens is your body mobilizes many more fat cells than it can actually oxidize (burn).

This is wrong for several reasons.

1. Research has shown that the total amount of fatty acids available regulates fat oxidation rates.

While your body may not be able to burn all of the fatty acids mobilized during fasted cardio, the more it has available, the more it burns. Thus, it’s not surprising that…

2. Research has also shown that ingestion of carbohydrate reduces fat oxidation while at rest and when ingested before exercise.

I’ve scoured the literature and based on what I’ve found, it’s very clear: total fat oxidation is just higher with fasted cardio than fed. The following graph from this study shows this nicely:

F5.large

CC had carbs 30 minutes before and during exercise; PC had a placebo drink 30 minutes before and carbs during exercise; CP had carbs 30 minutes before and a placebo drink during exercise; and PP received a placebo drink both before and during exercise (this was the fasted group).

And as you can see, PP burned the most fat throughout the entire workout.

Now, ingested before exercise is a key phrase here because the study most commonly cited as “proof” that fasted cardio is a waste of time showed that when carbohydrates are ingested afterexercise has begun (30 minutes after, in this case), then fat oxidation rates aren’t changed until after 80 to 90 minutes of exercise.

Researchers noted that this effect is likely due to the fact that the insulin response to carbohydrate ingestion during moderate-intensity exercise is almost completely suppressed. Thus, insulin levels remain more or less unchanged from their pre-workout (fasted) levels and fat oxidation rates stay the same.

That’s interesting, but who starts their workouts fasted and then eats carbs 30 minutes into them? Nobody. We eat our carbs anywhere from 15 to 30 minutes before we exercise, and as you now know, this reduces both lipolysis and fat oxidations rates and thus reduces the total amount of fat we lose in the workouts.

So, the bottom line is when we consider all the available research, it’s clear that fasted cardio results in a bit more fat loss than “fed” cardio, and thus is worthwhile.

Fasted cardio results in more fat loss than ‘fed’ cardio. Here’s how:

CLICK TO TWEET

Total fat loss isn’t the only reason I like fasted cardio, though. It also helps eliminate “stubborn” fat in particular.

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How Fasted Cardio Helps Get Rid of “Stubborn” Fat

fasted cardio results

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, obliques, and lower back.

This isn’t a genetic curse–it’s simply a physiological mechanism.

You see, your body uses chemicals known as “catecholamines” to break fat cells down into usable energy. Catecholamines travel through your blood and “attach” to receptors on fat cells, which then trigger the release of the energy stored within the cells so it can be burned off.

Fat cells have two types of receptors for catecholamines, however: 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 the 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-recepors than beta.

Another problem with these “stubborn fat” areas 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 to keep the catecholamines away.

Now, how does fasted cardio help?

Well, 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, resulting in more mobilization of it.

This is where I’ve personally really noticed a difference in cutting with and without fasted training. When I include fasted training (both cardio and weightlifting), the journey from about 9% to 6%, where the majority of the fat you’re losing is the “stubborn” stuff, is noticeably faster than when I don’t.

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What Type of Fasted Cardio is Best?

fasted cardio good or bad

If you’re familiar with my work, you know that when it comes to cardio, I’m a big fan of high-intensity interval training.

Studies such as those conducted by Laval University, East Tennessee State University, Baylor College of Medicine, and the University of New South Wales have conclusively proven that shorter sessions of high-intensity cardio result in greater fat loss over time than longer, low-intensity sessions.

In fact, a study conducted by The University of Western Ontario showed that doing just 4 – 6 30-second sprints burns more fat over time than 60 minutes of incline treadmill walking (one of the staples of “bodybuilding cardio”).

Furthermore, keeping your cardio sessions shorter helps you preserve muscle and strength.

This is especially relevant to fasted cardio as it accelerates muscle degradation, and the longer you train in a fated state, the more muscle you lose (we’ll talk more about how to combat this in a minute).

All that said, some people say HIIT performed in a fasted state is silly because fat oxidation rates are much lower during HIIT exercise.

Well, while it’s true that fat oxidation rates decline as cardio intensity increases (as glycogen then becomes the fuel of choice), there’s more to consider.

  • Research has shown that as you continue to perform regular high-intensity interval cardio sessions, your muscles “learn” to use less glycogen during workouts (thus increasing fat oxidation rates during the workouts), and your muscle cells also get better and better at oxidizing fats.

This latter point is particularly relevant to fasted training as, over time, high-intensity interval training increases the total amount of fatty acids your body is able to metabolize during workouts.

  • Research has shown that the post-exercise “afterburn” effect (EPOC) is greater with high-intensity interval training than with low-intensity steady-state cardio (about double, actually–13% vs. 7%).

The actual amount of additional calories burned due to HIIT’s greater “afterburn” effect will probably never be more than 50 to 80, but hey, that adds up over time.

  • Research has shown that high-intensity interval cardio is particularly good for getting rid of stubborn abdominal fat, including the dangerous accumulations of visceral fat.

Given all the above, I think it’s just a no-brainer to choose high-intensity interval cardio over low-intensity steady state.

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