Is Fasted Cardio Good For Fat Loss?
Are you looking for a short cut to fat loss or a way to squeeze every little drop out of every detail in your journey to get lean?
If you are, you’ve probably heard the term “fasted cardio”.
Is fasted cardio the “hack” that you need to be doing to shed that last bit of stubborn fat?
Is it the key thing that you’re not doing that could help you make more progress with your weight loss?
Or is it just another myth that you shouldn’t let distract you from the basics of fat loss?
Let’s dig in and find out.
Cardiovascular exercise, or “cardio” is any exercise that elevates the heart rate.
It comes in many shapes and sizes, and can look like a lot of different things.
Walking is cardio. Jogging is cardio. Biking is cardio. Climbing stairs is cardio.
Just like all exercise, there are a host of health benefits to doing “cardio” which are not limited to:
Increased blood flow and heart strength
Increased bone density
Decreased stress
Decreased risk of heart disease
Improved immune function
Weight loss
In the context of this article we will be talking about the last one today.
Weight loss.
Specifically fat loss.
Besides the other listed benefits above, we use cardio to burn calories. Why do we care about burning calories?
Because calories matter when it comes to fat loss. I mean, they really matter. Like they matter the most.
If you’re trying to lose fat you need to be paying close attention to your calories to make sure that you are burning more calories than you are eating.
Obviously the “eating” side of that equation is the most important (and the hardest part), but you can affect how many calories you are burning through exercise, like cardio. That’s one of the reasons (besides the health benefits) why we do it. To burn more calories, and have better fat loss because of it.
Quite simply put, it’s doing cardiovascular exercise when your body is in a “fasted” state vs. a “fed” state.
When we eat food, our pancreas releases insulin. Insulin directs our bodies to either use or store the nutrients/calories that we ate.
When we have insulin present in these elevated amounts due to eating food we are said to be in a “fed” state.
If we do cardio during this time we are said to be doing “fed cardio”.
Conversely, if we haven’t eaten for a long enough time such that our insulin levels are at a non-elevated baseline level, we’re said to be in a “fasted” state. Reaching a fasted state can take between 8 and 12 hours depending on what and how much you ate.
If we do cardio during this time we are said to be doing “fasted cardio”.
When we’re “fasted”, our bodies rely on stored carbohydrates in the form of liver glycogen as well as fat for energy.
The fact that when we do fasted cardio our body burns stored energy is what leads to some of the assumptions of why fasted cardio has become popular as a “fat loss hack”.
Think about it. If you exercise when you’re body is in a fasted state and is oxidizing fat for energy it would stand to reason that over an extended time you would burn more body fat right?
The other most common assumption is that since insulin levels are low while doing fasted cardio that the body will be optimally set up for even more fat-burning potential since when elevated, insulin tells our bodies to burn carbohydrates.
Well as is usually the case, smart people have already wondered enough about this to get grants and do research on these matters that we get to benefit from.
The research on this topic actually goes back at least into the 1970’s. A 1976 study had participants doing 4 hour-long cardio sessions (no thank you!). They divided the participants into two groups. One group consumed sugar 90 minutes into the 4-hour session and the other group stayed un-fed the entire 4 hours.
After eating sugar, which triggers insulin, that group started burning glucose at a much higher rate than the fasted group which continued burning more fat than glucose for the entire 4 hours.
This is most likely the study that started the motor on the “fasted cardio is optimal for fat loss” train that still runs strong today.
Want to lose more body fat? Do your cardio fasted! Makes sense based on that study right?
Hold the train!
It’s been 40+ years since that study and inquiring minds have dug deeper into the topic since then.
As is the case many times with research, subsequent studies will broaden both the scope and duration of the original study.
A 2011 Study not only looked at the amount of fat that is burned DURING cardio, but also in the 12 hours AFTER the exercise is over.
Their findings did in part support the 1976 study showing that we do burn more fat DURING fasted cardio vs fed cardio, with the exception of high-intensity cardio.
However, as is the case with so many processes in our body, we adapt. When the researchers looked at the longer-term they found something interesting.
DURING the cardio, the fasted group burned more fat than the fed group.
HOWEVER… in the 12 hours AFTER doing cardio, the fasted group burned MORE carbohydrates and LESS fat.
In the 12 hours AFTER doing cardio, the fed group burned MORE fat and LESS carbohydrates.
Our bodies seek homeostasis and balance. We naturally shift our energy source as nutrients are more prevalent.
The study concluded that there was NO advantage in fat loss in doing cardio in the fasted state vs. the fed state.
Let’s keep looking though.
A longer-term study was done in 2014 that looked at a group of 20 women. They were divided into two equal groups. Both groups’ food intake was controlled by the study, and both groups were consuming 500 calories LESS than their estimated daily energy needs. In other words, they were all in a 500 calorie deficit per day.
Over the course of 4 weeks both groups performed three one-hour cardio sessions per week.
One group performed their sessions in a fasted state and the other in a fed state.
At the end of the study, both groups lost body fat. Since you’re a Digital Barbell reader you should NOT be surprised since you already know that a caloric deficit causes fat loss.
But which group lost MORE fat?
Neither. There was no significant difference in the amount of fat lost between the two groups.
Doing cardio in a fasted vs. fed state did not produce long-term advantages in fat loss.
Still not convinced?
Possibly the best evidence we have is a 2017 meta-analysis that looked at 5 different 4-6 week trials comparing fasted vs fed exercise. Once again, and not surprisingly there were NO meaningful differences in body fat loss in the analysis. They were sure to note that the number one factor that affected body fat loss in the subjects was (not surprisingly) calorie deficit.
I’m positive that there is still ongoing research on the topic currently, but for now we feel confident saying that doing cardio in a fasted state provides NO benefit to doing it in a fed state.
Remember how we’ve talked about the two different “states” our body can be in at different times? They are “catabolic” and “anabolic”. To recap briefly, when we’re in an anabolic state we are building muscle tissue. When we are in a catabolic state we are breaking muscle tissue down. When we’re fasted, we are in a catabolic state.
A 2003 study showed that muscle breakdown rates are elevated while training in a fasted, catabolic state. That means there can be higher levels of muscle loss from training fasted vs. fed.
We aren’t here to scare you or hype up things to make you worry, but let’s face it. Building muscle as an intermediate or advanced lifter isn’t easy, so why risk it? Will you notice the differences? I doubt it, but at least you are aware now.
When we talk about “cardio” we’re talking about exercise that raises our heart rate.
We do cardio for many different health benefits but also to burn calories so that we can burn fat.
We can choose to do cardio “fasted” when insulin levels are low or “fed” when we have eaten and insulin is elevated.
When we do cardio fasted we burn MORE fat WHILE exercising, but our bodies burn LESS fat the rest of the day to balance out the equation.
When we do cardio fed we burn LESS fat WHILE exercising, but we burn MORE fat during the rest of the day to balance out the equation.
New research shows that there is NO fat loss benefit overall to fasted vs. fed cardio.
Research also reaffirms that calorie deficit is THE MOST important factor for fat loss.
Training in fasted state may cause you to lose muscle due to the catabolic nature of being fasted.
At the end of the day, your nutrition is the #1 factor in your fat loss progress. If you ignore it you will be frustrated for life.
If you need to burn more calories per day to affect your “calories out” side of the energy balance equation, cardio is a tool that you can use.
If you’re super concerned about losing muscle, do it after a meal.
If you’re not really worried about it, do it fasted.
It’s not worth losing sleep or arguing with friends over.
If you need help with your training & nutrition, we can help.
Download our free Calorie & Nutrition Guide HERE.
If you’re tired of spinning your wheels with workouts that aren’t getting results, apply for coaching HERE.