If you’re familiar with intermittent fasting then fasted cardio is something you may or may not be doing already. However, if you’re not then let me explain.
Fasted cardio is when you do exercise in a completely fasted state to help burn fat.
It’s not essential for fat loss and you can get lean without doing it. However, there is some evidence that shows you may be able to get leaner, faster using fasted cardio.
Additionally, when done properly fasted cardio can also help you lose more stubborn body fat.
This can be useful for anyone who struggles to lose that last bit of fat from their abs and love handles, which is most people.
I know this sounds great, but it comes with a big downside if you get it wrong and can end up losing your muscle mass and becoming skinny fat instead of lean.
I know this isn’t what you want so in this article we’re going to breakdown exactly what need to do and will cover;
How lose fat (a quick recap)
What is fasted cardio?
When it comes to losing fat, your diet is the single most important factor, and this is because of the energy balance equation.
The energy balance equation has 3 irrefutable rules which are as follows;
You will always be in one of these states, which means to lose weight you must create and maintain a calorie deficit. This is important because doing cardio whether it’s fasted or fed can help you create and maintain a calorie deficit but only if your diet is in order.
No amount of exercise can help you reach your fat loss goals if you’re not eating the right number of calories and getting the right macronutrients.
Put simply fasted cardio is doing exercise in a completely fasted state. This is generally 8 – 12 hours after your last meal when your body insulin levels are back at base levels and you’re no longer digesting food
Anything other than this is consider fed cardio with the difference between the 2 is how your body uses energy.
When doing fed cardio your body draws on the food you most recently ate to provide the energy you need, whereas when you’re in a fasted state your body draws on stored fat and glycogen for the energy it needs.
Fasted cardio has some unique benefits that you don’t necessarily get when training in a fed state. Research (1) shows that exercising when fasted increases the rates of 2 processes that are important to fat loss; lipolysis and fat oxidation (2).
What this means is that when you exercise in a fasted state your body becomes more efficient at mobilising and then burning fat compared to exercising in a fasted state.
Additionally, and quite importantly, there is evidence (3) showing that when you’re in a fasted state blood flow to your stomach is increased. This is good news as increased blood flow to this area translates to more fat burning chemicals reaching there and more total fat loss as a result.
In short, fasted cardio can help you burn more fat, particularly stubborn fat like that around the hips and stomach.
In fact, some research (4) shows that fasted cardio may burn up to 20% more body fat than non-fasted cardio with additional studies (5) showing that whilst fasted cardio has no benefits for total weight loss when compared to fed cardio it does help participants burn more fat.
What this means is you can get lean with both fasted and fed cardio but doing fasted cardio will help you improve body composition faster as you lose more body fat.
Ok, so we know the benefits of doing fasted cardio but what are the disadvantages.
The main one is the increase in muscle breakdown rates (6) associated with training in a fasted state. Sure, the effects aren’t going to massive but due to the fact it can be difficult to build muscle for lots of people, it can be enough to matter.
This becomes an issue when your body cannot keep up with the amount of repair your body needs as a result of the damage and break down from training.
Now, don’t get me wrong muscle damage and break down from training is a normal process, the difference is when you’re in a fasted state your body doesn’t have the nutrients it needs to keep up with the repairs it needs to do.
Over time this could result in less muscle growth or even muscle loss.
In addition to this, you may find that when you first switch to fasted cardio your workouts lack their usual intensity. Again, this is a normal part of training fasted and most people will find their energy and focus is lower when they first switch over.
After the first couple of weeks, you will adjust and things should go back to normal. You just have to accept the initial dip in performance and be willing to wait it out.
This means whilst fasted cardio can help you lose fat, particularly stubborn fat, faster it also has some potential downsides that you need to be aware of.
When it comes to fasting and weightlifting, it can also be just as effective as fasted cardio at burning stubborn body fat by ramping up the production of fat-burning chemicals in your body (7).
However, like with doing fasted cardio, it’s normal to see a drop in strength for the first few weeks as your body adjusts to training in a fasted state. This is only temporary and is the result of having less muscle glycogen (8) to fuel your workouts.
You see carbs improve workout performance and by taking them away you lose the performance benefits they give you.
There is research (9) showing that your body can adapt to training in a fasted state and use your glycogen stores more efficiently, but you may find that your fasted workouts are never quite as good as your fed workouts.
For this reason, you may want to do fasted cardio but stick to doing your weightlifting in a fed state like normal, particularly if you have body composition goals that include building or maintaining muscle.
As we touched on earlier fasted cardio is not much better at burning fat when compared to fed cardio (10), which is why the type of cardio you do matters.
When it comes to doing fasted cardio you really want to do high-intensity interval training (HIIT) to get the best results. This particularly important the leaner you get and the more stubborn fat you have to lose.
This is primarily because HIIT when compared to steady-state cardio, not only burns more calories but does it in less time (11).
For example, in one study (12) 2 groups were compared;
At the end of the study, they found that the sprint group lost more fat. Not only this but they did it in a fraction of the time.
If you’re looking to maximise your fat loss and minimise the time spent doing cardio, then HIIT is the way forward. In addition, HIIT also (13);
It’s clear for all to see that if you’re only going to do a small amount of cardio per week then HIIT is the way to go for a maximum return on your effort.
Add to this the fact that when you do it in a fasted state these effects are amplified and it’s a no brainer.
How to do it:
Just in case you were thinking of doing steady-state cardio for your fasted training, note that prolonged bouts of exercise in a fasted state have been shown to increase the breakdown of muscle protein putting you at a greater risk of losing fat and muscle (14).
Play it smart and stick with HIIT training or eat first if you want to do longer duration bouts of cardio.
I know I just answered this question, but I wanted to go into a little more detail to show you why it’s best to do your fasted cardio first thing in the morning.
Ok, so let’s say that you eat dinner between 6 – 8 pm and you don’t eat again that day, then when you wake up the next morning your insulin will be at baseline levels.
Additionally, research (15) shows that fat oxidation rates are highest 6+ into your fast and because you’ve spent the night asleep you can guarantee you’ll be in a fasted state.
Remember, this is important because eating elevates your insulin levels and puts you into a fed state. When you’re in a fed state you don’t get the benefits of increased fat mobilisation and fat burning.
This means you’re in the perfect position to get out there and do some fasted cardio, no additional preparation required. No wonder doing fasted cardio first thing in the morning is so popular.
Now, this doesn’t mean you can’t do fasted cardio later in the day, but it does make it trickier to pull off.
Firstly, if you’re going to fast until the afternoon and then workout you may very well find that your performance deteriorates as you get further through your day and deeper into your fast.
Secondly, if you’re going to eat during the first part of the day and aim to get back into a fasted state for the afternoon or evening this requires careful planning as even have a small amount of sugar or serving of whey protein is enough to raise your insulin levels for a number of hours (16, 17).
For most people, the difficulty of managing their meals in a way that allows them to train fasted in the afternoon or evening is too difficult when balancing work, family and everything else.
Remember, that whilst fasted cardio can offer a few benefits for those looking to lose that stubborn fat it is no necessary and if you can’t make it work then don’t feel like you have to force it.
This is a popular question particularly amongst those following an intermittent fasting protocol.
The short answer is yes. You should eat after you’ve done your fasted cardio and the primary reason for this is preventing the increase in muscle breakdown that occurs after fasted training (18).
Sure, technically speaking you could eke out a little more fat loss if you held off eating for a while but for most people, the risk of losing muscle mass isn’t worth the small increase in fat gain they might receive.
This is important as if you remember from earlier the biggest downside of fasted training is potential muscle loss. By breaking your fast after your workout, you help to negate this and make fasted training more effective.
For more details on the best post-workout meals, check this out.
Fasted cardio is the name given to any exercise done when in a completely fasted state i.e. when your body is no longer digesting food and your insulin levels, are at baseline.
When done correctly it can not only help you lose more fat, but it can specifically help you lose the last bits of stubborn fat that most people struggle with. However, when done incorrectly it can cause muscle loss and skinny fat syndrome.
To do it right you want to keep cardio to 2 – 3 sessions a week, either after your weightlifting or on rest days and do some form of HIIT like sprints.
Aim to workout first thing in the morning and eat a mix of protein and carbohydrates once you’ve finished.