Do You Need Fasted Cardio?

It seems everywhere you look these days there’s a new gimmick boasting faster fat loss. 7 day this, 6 minute that. The ONE thing you’re missing. Of course for people wanting to slim down these headlines and new fads are quite appealing. Some of these fads are pure junk, but occasionally something comes along that is actually backed in science and does what it says it does.

Fasted cardio just happens to fall into that category. But, does it necessarily trump regular cardio, and should YOU use it as a tool in your fat loss arsenal?

Cardio, or any exercise for that matter, alone is a poor way to lose weight. If you don’t have your kitchen in order results from exercise will do little to move the needle in terms of fat loss. Dialing in a solid nutrition plan and pairing it with exercise does, however, work some synergistic magic to drop the flab.

Rather than rekindle the age old debate of which type of exercise is best (hint: it’s weights), we’ll focus on cardio, better known as cardiovascular or aerobic training. Although not necessary for fat loss, it can be a helpful tool when used correctly.

I come from an endurance sports background. Unhappy with my body image at the time, my quest to shape a perfect body involved piling on more and more mileage and doing longer distance races to combat the fat. While I enjoyed it, it didn’t work because of my diet and too much exercise without adequate recovery.

One thing the endurance sport industry drives home to its participants is the supposed need to fuel. You’re told you need some magic drink or gel before, during, and after each workout. I bought into and was always frustrated that I “needed” to eat breakfast before running a 3am 14 miler.

It turns out there is another way. That’s simply to go do the workout in a fasted state, without eating anything beforehand, or during. It turns out our bodies are exquisite pieces of machinery and they can find plenty of fuel (ie. your own body fat) when normal sources aren’t present.

Studies have shown that fasted cardio results in greater breakdown of fat cells (lipolysis) and increased fatty acid oxidation (burning fat for energy). This is because your body is already in a fasted state after your night’s rest and it is mainly burning fat from lipolysis and converting the resulting fatty acids into energy via beta oxidation.

Eat some breakfast, or ingest a gel, and you are introducing glucose, causing a spike of the hormone insulin (the body’s response to clear blood sugar). In the presence of insulin your body does not break down fat cells for energy usage (insulin is a storage hormone) Now your body will work to clear blood glucose and preferentially use that sugar just introduced to fuel your workout.

This simplistic model makes a pretty clear case for fasted cardio, but as it usually is when it comes diet and exercise there are multiple factors to consider. For one, the studies only compared fat breakdown and usage during the actual exercise. There is this thing know as excess post-exercise oxygen consumption, or EPOC, in which the body continues to burn energy to erase the oxygen debt it was just put in. This is why you’ve been told exercise increases metabolism.

For steady state cardio, in which you run at a continuous moderate rate, there is very little EPOC compared to a high intensity interval session, such as hill sprints. This is why you’ve been told to use HIIT for fate loss, which I’m a huge proponent of, instead of just heading out for a jog. The calorie burn after the exercise is where the magic happens.

Using the simplified fat burning model described above, one can rationalize that if you’re doing steady state cardio and looking to burn fat it is advantageous to do so in the fasted state. For HIIT training, the advantage may be there, but it may not be as pronounced due to the contribution from EPOC.

So where do we stand on resolving the original question of whether or not you need to do fasted cardio? Well, first there is another factor to consider and that is how well your body responds to exercise in the fasted state. If you are one of the many consuming the standard American diet filled with sugars and grains your body likely doesn’t do real well in the fasted state. You’ve taught it to survive on a constant influx of carbohydrate for it’s fueling needs and when those carbs aren’t present in can present problems and make a fasted workout quite difficult.

If you’re like me and have taught your body to use fat for fuel a fasted workout is no big deal. I’m a huge fan of intermittent fasting, which can help get you used to fasted state. In addition I eat fairly high fat, low carb, which can also help train your body to utilize fat for the majority of its energy needs. I can roll out of bed, not hungry, and knock out a 25 minute HIIT session with no noticeable sluggishness or irritation.

So is it something YOU need to do?

My advice: give it a shot.

More than once.

One bad session shouldn’t keep you from continuing, but after a few you’ll catch on pretty quick whether or not your body can handle it. If you feel fatigued or light headed every time stop doing it until you are more fat adapted. It’s definitely not for everyone and while there are clear benefits it’s not the end all be all of fat loss. There are many tools for that job. Pick the ones that work best for you and leave the rest in the box for the times that you may need them.

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