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.
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:
Alright, now we know what fasted cardio is. Let’s now look at how fed and fasted states relate to fat burning and storage.
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:
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?
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…
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:
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 after exercise 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.
Total fat loss isn’t the only reason I like fasted cardio, though. It also helps eliminate “stubborn” fat in particular.
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.
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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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.
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.
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.
Given all the above, I think it’s just a no-brainer to choose high-intensity interval cardio over low-intensity steady state.
Some people say doing so puts too much strain on your body and will cause overtraining, but I’ve yet to run into that problem with my own body or the thousands of people I’ve worked with. (Seriously–I’ve never had one person write me complaining about feeling overtrained soon after incorporating fasted HIIT into their workout routines).
That’s probably because I recommend a very moderate amount of high-intensity interval cardio when dieting for fat loss–no more than 4 sessions per week, and no more than 25 to 30 minutes per session.
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.
I do all my exercise–both weightlifting and cardio–fasted when I’m dieting for weight loss and as I said earlier, the stubborn fat disappears faster than when I exercise in a fed state.
A caveat, though: don’t be surprised if you’re noticeably weaker during your first couple of weeks of switching from fed weightlifting to fasted.
You will lose some reps on your big lifts, if not across the board. This isn’t because you’re losing muscle, it’s simply because eating a significant amount of carbohydrate before you work out dramatically improves your performance in the gym. Take the carbs away and you lose the “boost.” Add them back and it returns.
That said, as I noted earlier, your body slowly adapts to training in the fasted state, learning to preserve glycogen stores and thus preserve performance. Nevertheless, I’ve found that my lifts while fasted are just never as good as my lifts while fed.
If you’re going to train fasted, you should seriously consider using the following supplements to squeeze as much fat loss as possible out of it and negate its one big downside (which you’ll read about below).
The following supplements are what I use when dieting for fat loss and, like fasted training, they make the fat loss even noticeably faster with no unwanted side effects. There’s really no reason not to add them to your routine.
So, let’s go over each supplement I recommend and why.
In the spirit of full disclosure, I want you to know that the supplements I recommend in this article are not just what I personally use but they are from my supplement line, LEGION.
As you probably know, the supplement industry is notorious for its lies and shenanigans. The truth is the majority of the supplements you see in the magazines and on the shelves aren’t going to help you reach your goals faster.
That’s why I decided to create the products I myself have always wanted: science-based formulations, clinically effective dosages of all ingredients, no fillers or unnecessary junk, and natural sweetening and flavoring.
And if you like what you see and decide to support my work…you’re awesome. 🙂 It’s because of people like you that I get to spend my time writing articles like this that help others get into the best shape of their lives.
There is a downside to fasted training that you should know about: muscle breakdown is dramatically increased.
This is bad simply because too much muscle breakdown impairs total muscle growth over time. Preventing this is simple, though.
β-Hydroxy β-Methylbutyrate (also known as HMB) is a substance formed when your body metabolizes the amino acid leucine, which is an amino acid that directly 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 can’t break your fasted state.
This makes 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.
In terms of which specific HMB supplement I recommend, I’ve included a clinically effective dosage in every serving of my pre-workout fat burner FORGE.
FORGE is a fat burner made specifically for use with fasted training and it contains clinically effective dosages of…
Research shows that supplementation with CDP-choline improves attentional focus, and I included this in FORGE because most people find fasted training more mentally draining than fed training and CDP-choline can help counteract this.
The bottom line is FORGE helps you lose fat–and “stubborn” fat in particular–faster, preserve muscle, and maintain training intensity and mental sharpness.
As weight loss boils down to energy consumed vs. energy expended, caffeine helps you lose fat by increasing your body’s daily energy expenditure.
Part of maximizing the fat loss benefits of caffeine is preventing your body from building up too much of a tolerance, however. The best way to do this is to limit intake, of course.
Here’s what I recommend:
Personally I get my caffeine from my pre-workout PULSE, which contains a dehydrated and concentrated form of caffeine (caffeine anhydrous) shown to be more effective for improving performance than what is naturally found in beverages like coffee.
PULSE also contains clinically effective dosages of 4 other ingredients scientifically proven to improve workout performance:
The bottom line is if you want to know what a pre-workout is supposed to feel like…if you want to experience the type of energy rush and performance boost that only clinically effective dosages of scientifically validated ingredients can deliver…then you want to try PULSE.
Yohimbine is made from the Pausinystalia yohimbe plant, and it helps the body “tap into” fat stores.
(Not a very technical explanation, I know–if you want to know exactly how it works, check out this article of mine on how to lose stubborn fat.)
I’ve cut both with and without fasted training and yohimbine and I can say with absolutely certainty that with is noticeably faster. So much so that I think the biggest benefits of fasted training are that it lets you use yohimbine and it makes the other supplements discussed in this article more effective.
By itself, fasted training will make a slight difference in how quickly you lose fat. Combined with these supplements, however, it’s quite dramatic.
In terms of dosages, research has shown that .2 mg/kg of body weight is sufficient for fat loss purposes, and that ingesting it prior to exercise is particularly effective.
Some people get overly jittery from yohimbine, so I recommend you start with .1 mg/kg of body weight to assess tolerance. If you feel fine, then increase to the clinically effective dosage of .2 mg/kg.
Furthermore, yohimbine can raise blood pressure. If you have high blood pressure, I don’t recommend you use it.
In terms of which specific yohimbine supplement I recommend, you’re probably not surprised that I’ve included a clinically effective dosage in every serving of my pre-workout fat burner FORGE.
PHOENIX’s caffeine-free formulation is quite a bit different than FORGE’s and is actually made to be “stacked” with it (taken together).
PHOENIX helps you burn fat in three different ways:
It accomplishes this through clinically effective dosages of several ingredients, including…
Through these mechanisms, naringin also works synergistically with synephrine and hesperidin to further accelerate the basal metabolic rate.
Here’s what I take before my fasted training sessions:
(NOTE: Taking green tea extract, which is in PHOENIX, on an empty stomach can make some people nauseous. If that happens to you, take it with food and you’ll be fine.)
When I’m dieting for fat loss, I lift weights in a fasted state 5 days per week and do 25 to 30 minutes of HIIT cardio in a fasted state 3 to 4 times per week.
On the days where I’m doing both weightlifting and cardio, I take the above before both training sessions and have no issues.
You don’t have to train fasted to lose fat and get lean, but it’s a valuable strategy that you should consider trying.
This is especially true if you’re lean and wanting to get really lean because you’re going to be dealing mainly with stubborn fat stores that can be very slow to disappear with just diet and exercise alone.
I’ve also found that proper supplementation, as laid out in this article, is particularly effective when combined with fasted training. The hormones and mechanisms involved in fat lipolysis and oxidation work best in the low-insulin fasted state and thus so do supplements that help your body burn more fat.