Whether you enjoy cardio or not, you probably know that it helps you lose fat faster.
On the other hand, you also probably know that doing too much cardio makes it harder to make muscle and strength gains.
Therefore, the more you care about your body composition, the more you might wonder how you can reduce the “minimum effective dose” of cardio required to get the bod you really want.
In other words, how can you reach your fitness goals while doing as little cardio as possible?
Many people say fasted cardio is the ticket because it burns significantly more fat than non-fasted cardio.
It’s also commonly claimed that fasted cardio is particularly helpful for eliminating the “stubborn” fat covering your stomach, love handles, and lower back (men), and butt, thighs, and hips (women).
And then there are those that disagree. Fasted cardio does not help you lose fat faster, they proclaim, and actually makes it harder to get the body you really want by accelerating muscle loss and making your workouts a lot harder than they need to be.
Well, both groups … and neither of them.
The truth is that fasted cardio can’t help you lose fat faster, but it can help you lose stubborn fat faster if you do it right. If you do it wrong, though, then all you’re likely to get from it over traditional “fed” cardio is smaller and weaker muscles.
Case in point: I’ve used fasted cardio successfully to cut down to ~7% body fat while losing little to no muscle and strength:
I didn’t simply go for a jog before breakfast to get there, though.
I followed a very specific fasted cardio regimen to make it work, and I’m going to break down exactly what I did in this article. And by the end, you’re going to understand:
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Many people think fasted cardio is simply training on an “empty stomach,” which they usually think is simply a stomach that “feels empty.”
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. 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” low (or “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 that include a mix of protein, carbs, fat, and fiber digest slower than smaller meals that are mostly composed of one or two macronutrients (like an apple, which is mostly carbs).
For example, research shows if you eat about 600 calories of pizza (providing about 37 grams of protein, 17 grams of fat, and 75 grams of carbs), your insulin levels will remain at double their baseline level for at least five hours.
On the other hand, if you eat a smaller, simpler meal like a single scoop of whey protein isolate, which only contains about 100 calories, 20 grams of protein, and only trace amounts of fat and carbs, your insulin levels will fall back to baseline levels in a few hours.
Your body moves in and out of these fed and fasted states several times a day, so timing your exercise correctly is the key to doing fasted cardio.
So, to recap:
Alright, now we know what fasted cardio is. Let’s now look at what science says about whether or not it can help you lose fat faster.
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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 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 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.
What does the science say?
There’s little doubt that fasted cardio burns significantly more fat than fed cardio.
In 2016, a group of scientists from Federal University of Rio Grande do Sul in Brazil looked at 27 studies on this topic, and concluded that “… aerobic exercise performed in the fasted state induces higher fat oxidation than exercise performed in the fed state.”
The main reason is simple: it’s very easy for the body to convert carbohydrate into fuel during exercise. Thus, when more of it is available, as is the case after eating a meal containing carbs, your body burns more carbs and less fat for fuel.
So, we know that training fasted causes you to burn more fat during your workouts. So far so good.
We also know, though, 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.
The real question, then, is does that small increase in fasted fat burning translate into a significant boost in fat loss over the course of the entire day?
That’s what a group of scientists from the University of Padua wanted to find out in a study they conducted in 2011. They split eight men into two groups:
For the workouts, everyone ran on a treadmill for 36 minutes at a moderate pace. The researchers measured what percentage of calories the subjects were burning from carbs versus fat before and 12 and 24 hours after their workouts.
As expected, the group that trained fasted burned more fat during the workouts. Later in the day, though, they burned significantly more calories from carbs and less from fat.
The group that trained fed experienced the opposite: they burned more carbs during the workout and more fat during the rest of the day.
When the researchers averaged it all out, both groups burned the same amount of body fat and carbs throughout the day, meaning that fasted cardio offered no clear fat loss advantage.
The body uses whatever fuel it has available for energy, and also prioritizes nutrients in a specific order:
Therefore, when carbohydrates are readily available, the body prefers to burn them over body fat, and when less glucose is available, it prefers to rely more on dietary fat and body fat stores for its energy needs.
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.
One shortcoming of this study is that it only measured fat burning over the course of a single day. Is it possible that the group that did fasted cardio would have lost more fat than the fed group if they kept this up for several weeks?
That’s what scientists from Lehman College wanted to find out in a 2014 study. They split 20, 20-year old women into two groups:
Both groups ate their last meal at least 12 hours before reporting to the lab to ensure they were in a fully fasted state.
Under the supervision of the researchers, everyone did one hour of jogging on a treadmill three times per week for four weeks. The researchers had both groups follow a diet that kept them in a 500 calorie deficit every day.
At the end of the study, both groups reduced their body fat percentage by about 1%, but there was no significant difference between groups.
Once again, fasted cardio didn’t cause any more total fat loss than regular fed cardio.
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 for easy energy.
To make matters worse, the fitter you become, the more your body will tap these intramuscular triglycerides instead of going to body fat stored in other places (like the stuff covering your abs).
Although it’s implied in everything we just discussed, let’s address this point directly.
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:
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.
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.
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-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 parts of your body that are already fairly lean.
For example, if you’re a guy it’s common for your chest, forearms, and calves to keep getting leaner and leaner, while your lower abs, love handles, and lower back refuse to budge. If you’re a woman, it’s common for your legs, abs, and arms to get leaner while your butt, hips, and thighs remain damn near unchanged.
Thus, once you get relatively lean, the more “stubborn” fat you can lose, the bigger the impact on your physique. Losing just a pound or two of fat from the “right places” does a lot more in the mirror than several pounds from areas of your body that are already lean.
How does fasted cardio help with this, you’re wondering?
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 greater stubborn fat mobilization.
This means that while fasted cardio won’t help you lose more total fat every day, it will help you lose more of the fat you want to lose most.
And especially if you combine it with the right supplements, which includes two in particular I want to draw special attention to: yohimbine and synephrine.
A good example yohimbine’s effectiveness comes from a study conducted by scientists at the Université Paul Sabatier in France.
The researchers had six young men report to the lab and undergo both of the following protocols with one week between each:
As you can see in the graph below, blood levels of free fatty acids doubled when they took yohimbine after an overnight fast, yet remained unchanged when they took yohimbine after eating breakfast.
(I don’t want to wander off into the weeds here, but free fatty acid [FFA] levels are a reliable indicator of how much body fat is being broken down for burning, also known as fat mobilization.)
The same scientists also carried out another experiment on eight more men in the same study. In this case, they had everyone undergo all three of the following protocols with one week between each:
They found that both yohimbine and exercise alone increased fat mobilization 50 to 100% above baseline, respectively. When people combined both exercise and yohimbine, though, the effects were additive, and fat mobilization increased over 150%.
Here’s what the results looked like:
Yohimbine’s fat-burning effects go further than that, however: it can also help your body better “tap into” and burn stubborn fat stores.
It accomplishes this by attaching itself to and more or less deactivating 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 bind to the beta receptors on fat cells instead, which stimulate fat loss.
In other words, yohimbine prevents your fat cells’ alpha receptors from preventing fat loss.
Furthermore, remember which fat deposits are generally highest in alpha receptors? That’s right, the “hard-to-lose” bits that we want to eliminate most, which is why yohimbine is considered particularly effective for burning away stubborn fat holdouts.
I’m using “considered” advisedly there because while conclusive studies on yohimbine and stubborn fat in particular haven’t been done yet, we do have strong indirect evidence for our case.
For instance, in a study conducted by scientists at the Institute of Sports Medicine in Serbia, 20 elite level soccer (“football” to you non-’Muricans) players into two groups:
The scientists had both groups follow their normal soccer training and a new strength training plan, and after three weeks, the yohimbine group lost five pounds of fat, whereas the placebo group didn’t lose any.
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. Thus, a fair amount of the rather large amount of fat they lost was assuredly belly fat because it’s very unlikely any of these guys had pounds of intramuscular fat stores to burn.
All this is why I believe that yohimbine makes fasted cardio more effective than fed cardio for the purposes of losing fat, and losing stubborn fat in particular.
Now, a counter argument could be that as neat as yohimbine is, your body will simply compensate even more by burning even less fat throughout the day, resulting in more or less the same 24-hour fat loss as with fed cardio.
A fair argument, but I don’t think it’s the case.
Based on years of experience with my own body and working with tens of thousands of people through my books and websites, I’m fairly convinced at this point that yohimbine and fasted training does indeed speed up fat loss in a meaningful way.
Synephrine is a naturally occurring substance that’s particularly abundant in the bitter orange fruit, which is why it’s often referred to by that name.
It’s chemically similar to the ephedrine and pseudoephedrine found in many over-the-counter cold/allergy medications and weight loss and energy supplements that contain ma huang.
Accordingly, synephrine impacts the central nervous system and increases basal metabolic rate, which accounts for up to 70% of your daily calorie expenditure, and also increases the thermic effect of food, which is the energy cost of digesting and processing what you eat.
There’s also evidence that synephrine blocks the alpha receptors on fat cells, which means that it can speed up stubborn fat loss in a manner similar to yohimbine, which is why I particularly like it combined with fasted cardio.
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 to 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 fasted 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 carbohydrate then becomes the fuel of choice), there’s more to consider.
This latter point is particularly relevant to fasted cardio 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 four 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 noticeably faster than when I do this than when I do all my training 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 carbohydrate during training, and thus maintain 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 two strategies to squeeze as much fat loss as possible out of it and negate its one big downside (which you’ll read about below).
Let’s start by going over each supplement I recommend and why.
The following five supplements are what I use when dieting for fat loss and, like fasted training, they make the stubborn fat loss noticeably faster with no unwanted side effects like muscle loss. There’s really no reason not to add them to your routine.
As you learned earlier, yohimbine is a supplement that boosts your metabolism and stubborn fat loss when taken before fasted training.
Some people get overly jittery from yohimbine, so I recommend you start with 0.1 mg/kg of body weight to assess tolerance. If you feel fine, then increase to the clinically effective dosage of 0.2 mg/kg.
To further increase fat mobilization during fasted cardio, you can also combine yohimbine with the stimulants caffeine and synephrine, which you’ll learn about in a moment.
Some people also don’t feel good when lifting weights after taking yohimbine, so if that’s the case with you I recommend you only take it before fasted cardio.
Furthermore, yohimbine can raise blood pressure so if you have high blood pressure, I don’t recommend you use it.
In terms of which specific yohimbine supplement I recommend, I’ve included a clinically effective dosage in my pre-workout fat burner Forge.
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, HMB is very good at preventing muscle breakdown, which means you’ll 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.
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) that works quickly in the body.
We recall that synephrine is an effective natural fat burner that will help you lose fat, and stubborn fat in particular, faster.
Research also shows the effects of synephrine are amplified when it’s taken with two other molecules that occur naturally in bitter orange fruit: naringin and hesperidin.
Naringin stimulates the production of a hormone called adiponectin, which is involved in the breakdown of fat cells, and it activates a type of receptor in fat cells that regulates fat mobilization (the PPARα receptor).
Through these mechanisms, naringin also works synergistically with synephrine and hesperidin to further accelerate the basal metabolic rate.
For all of these reasons, I included a clinically effective dosage of synephrine, naringin, and hesperidin in my natural fat burner, Phoenix.
Phoenix’s caffeine-free formulation is quite a bit different than Forge’s and is actually made to be “stacked” with it (taken together).
(I purposely left out the caffeine from both of these supplements, though, because chances are you’re like most people and would prefer not to get your caffeine from pills.)
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.
I’m often asked what to eat after fasted cardio, and my answer is this:
The same thing you’d eat after any workout—30 to 40 grams of protein and about the same amount of carbs. You can adjust those numbers based on your target calories and macros, but they’re good starting places for most people.
Some people would disagree with that advice and say that you should wait a bit 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 right after or several hours after your workouts.
Furthermore, with or without supplements, the increase in stubborn fat burning that occurs during fasted training disappears quickly once you stop working out.
In other words, 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.
So by delaying your post-workout meal after fasted training, you’re setting yourself up for maximum post-workout muscle loss.
One of the most effective ways to decrease muscle protein breakdown after a workout (fasted or otherwise) is to raise your insulin levels, and the best way to do that is to eat a protein- and carb-rich meal.
By itself, fasted cardio isn’t going to help you lose more fat than fed cardio.
When you combine fasted cardio with the right supplements, though, then it becomes a valuable fat loss 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.
In terms of what kind of cardio you should do, I recommend you stick with HIIT, which results in more fat loss in less time than low intensity steady state cardio.
When cutting, you can do your weightlifting workouts fasted to accelerate stubborn fat loss even further. You’ll probably notice a slight drop in strength when you start lifting fasted, but that comes back when you switch back to fed training.
I also recommend you have a post-workout meal within 30 minutes of your fasted workouts to minimize muscle loss.
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.
Before each workout, I take the following supplements:
Then I eat a post-workout meal that contains at least ~40 grams of protein and about the same number of carbs after each workout.
If you want to learn more about how to set up a diet for fat loss, including …
… then you want to check out this article: