by Katie Hoehn January 23, 2023 5 min read
On paper, it seems like weight loss should be pretty straightforward.
You burn more calories than you consume; so eat less, work out more, and as a result ... you’ll burn fat and lose weight, right?
Sounds simple enough...
Well, it doesn’t work exactly like this in practice, and things can get a little more complicated.
Let me explain...
Your body doesn’t want to lose ALL of its reserved fat. It likes to have a nice emergency storage of available calories on hand "just in case."
Your body's main priority is to keep you alive, which makes a lot of sense!
Once you start dipping into that reserve, it'll try to adapt. How? By beginning to slow down your metabolism so your ‘energy out’ doesn’t surpass your ‘energy in.’
Have you ever heard of a weight loss plateau? Maybe you’ve experienced one or maybe you're going through one now.
To get past them, people often try to get creative ... and that’s one of the main reasons why fasted cardio has gained a lot of popularity in recent years.
Fasted cardio is a workout approach involving aerobic exercise or cardio on an empty stomach.
Cardio exercise is effective and can offer a range of benefits, like heart health, blood sugar management, enhanced immunity, and more.
Fasted cardio attempts to add to these benefits by introducing fasting. You don't carb up. You don't lead with a pre-workout supplement. You just dive right in!
But why would you want to exercise without any fuel in the tank?
Well, the whole idea is that after a full night's sleep (or any kind of prolonged fasting) ... your body's energy reserves are depleted.
The energy reserves I'm referring to are the glycogen in your liver and muscles. To keep things simple, the term "glycogen" refers to the stored carbohydrates in your muscles and liver. (Side Note: muscle glycogen levels will not deplete significantly overnight).
This means that you won't have many easy, on-hand carbs for your body to pull from to fuel the workout.
So instead, your body starts burning fat. The more intense the workout, the more fat you burn.
Advocates of fasted cardio claim that by doing cardio when your body is least prepared (nutritionally), you can kick your metabolism into high gear. In theory, this can help you push past your weight loss plateaus and see better returns.
But, the truth about fasted cardio is much different. While it may accelerate fat loss in certain circumstances ... it's certainly not the weight loss breakthrough you're looking for.
Does fasted cardio burn more stored calories while you work out? The science suggests that it does not.
But ... that’s only looking at part of the picture.
For one, when your body needs calories and doesn’t have any glycogen to pull from, it may turn to fat … or it may go for protein.
As in, the protein that’s available in your muscle tissue.
There's evidence to suggest that fasted exercise increases muscle breakdown ... potentially twice as much muscle breakdown as opposed to when you're fed!
There’s also the simple fact that you need energy to exercise effectively. I mean, without the right fuel, intensity, and volume ... the overall positive impact of your workout may not be where it could be.
There’s more to consider about fat burning than just how much fat you burn at the gym.
Your body is constantly burning calories for fuel, even when you’re not trying to.
Eating, sleeping, and your everyday physical activity accounts for a lot of your daily calorie burn. Unless you are an athlete, this is probably how you are burning the majority of your calories too!
Believe it or not, there's evidence that suggests that taking some carbs before your workout can improve EPOC. EPOC stands for excess post-exercise oxygen consumption. This is what most people refer to as the "afterburn" ... or in other words, this keeps your body burning calories after the workout!
So is fasted cardio really as great as people claim it is? Maybe not, but we still have more to discuss...
Considering the points mentioned above, a lot of fitness professionals have an unclear view of fasted cardio.
But in terms of safety, fasted cardio doesn’t pose much risk.
Sure, you may feel lightheaded during or after your workouts. If your fasting includes avoiding water ... you also run the risk of experiencing dehydration. But those are the only real health risks of fasted cardio worth mentioning.
If you’re a healthy individual, fasted cardio should be perfectly safe.
But note, it’s unlikely to offer many additional benefits over standard cardio.
There are some potential benefits, just maybe not the ones that you might expect.
Unfortunately, fasted cardio doesn't burn more calories than un-fasted cardio while you exercise. Plus, a 2014 study concluded that, in terms of body composition changes (i.e. losing weight), both non-fasted and fasted cardio produce essentially the same results.
So, what are the benefits of fasted cardio? Well, they have more to do with your personal preference than anything else.
Do you get cramps or feel nauseous if you exercise after eating? Fasted cardio can help you avoid some of that gastrointestinal (GI) stress and help you keep your focus on the workout.
At the same time, some people simply prefer the feeling of exercising on an empty stomach.
But if you’re struggling through your workout or wishing you could enjoy a little breakfast before you get started ... then there’s really no reason to keep doing fasted cardio.
A question to ask yourself is, how are YOU able to perform at YOUR best? Because that is when you will get the most out of it.
Like I said, there aren’t too many reasons to commit to fasted cardio. There also aren’t any reasons to be afraid of trying it.
If you want to get into fasted cardio and see for yourself, here’s how to do it.
Just don’t eat before you exercise. That’s it.
Most people who do fasted cardio tend to set their workout schedules for early morning. That way, they can take advantage of the empty stomach following a full night’s sleep.
Just wake up and get started on your preferred aerobic exercises and you’ll be engaging in fasted cardio.
If you’re already practicing intermittent fasting throughout the day ... you can fit your fasted cardio sessions into those fasting periods as well.
Just make sure to listen to your body.
If you hate the feel of fasted cardio compared to how you feel doing un-fasted cardio, then stop doing it.
If you want to build muscle, lose weight, and improve your overall health ... then it makes sense to focus on your cardio training.
But don’t let your enthusiasm get the better of you.
Fasted cardio may feel like a more intense and more effective approach, but in the long run ... it doesn’t offer any additional benefits over traditional un-fasted cardio.
So feel free to lead with a pre-workout shake. Or don’t. It’s all just a matter of personal preference.
Want to learn more about cardio and get additional tracking and educational support?
Download the 1st Phorm App today!
From counting your macros to helping you create the perfect workout regimen ... we're here to help you transPHORM your life whether you do fasted cardio or not.
If you ever have any questions or need extra assistance ... we have you covered! We have a full staff of NASM Certified Personal Trainers and Nutrition Coaches who are here to help you for FREE.
Katie Hoehn Registered Dietitian ACE Certified Personal Trainer ACE Fitness Nutrition Specialist ACE Youth Fitness Specialist 1st Phorm App Advisor