Fasted Cardio for Strength Training: Pros and Cons

For years, I’ve done fasted cardio as my main form of cardio. I’ve tried all sorts of cardio routines: fasted, fed, high-intensity, intervals, low-intensity, even no intensity (i.e., no cardio)!

When I was working at Google, my schedule demanded that if I wanted to work out at all, I had to do it at 5 AM, so that’s what I did. I found that fasted, low-intensity cardio worked pretty well, and I didn’t mind doing it, so that’s what I’ve stuck with.

Since changing careers, I’m no longer saddled with a traditional work schedule, so I have a lot more flexibility to train when I want to. I’ve moved my lifting to early afternoons, when I’m feeling my best, and that’s made a huge difference in my training productivity. But I’ve never revisited the idea of fasted cardio. Every time I think about it, I get lost in the arguments for and against each — and, as I’ll explain, there are a lot of those arguments.

Recently, though, I’ve started to feel pretty stale on the fasted stuff. If you’ve been following my articles here on BarBend, you know that my number-one rule is to find what works for you – and that that usually requires a lot of trial and error. Since I haven’t even tried fed cardio in quite some time, I decided that I needed to revisit that habit.

Pros and Cons of Fasted Cardio

Like I mentioned above, you can do a quick Google search and find an overwhelming amount of evidence and arguments for and against fasted cardio. The proponents claim that your hormonal state is optimized for fat loss first thing in the morning, and that low glycogen stores will require the use of fat for fuel. Critics argue that fasted cardio increases muscle catabolism and hasn’t consistently shown greater amounts of fat loss.

Look, I’m a big believer in the scientific method, but when it comes to training, I think too many people put too much emphasis on formal studies and research. I really like how John Meadows puts it: “You can find a study to support anything, so you’re always going to be wrong.”

Instead, I think it’s better to focus on the more practical or tangible aspects of fasted and fed cardio. And of course, you can still make arguments for or against either:

In favor of fasted (first thing AM) cardio:

  • It’s really easy to come up for excuses to skip your cardio sessions later in the day — meetings come up, lunch runs long, whatever. Cranking them out first thing in the morning eliminates those (for the most part).
  • Your experience might be a bit easier: the gym will likely be empty if you get up early enough, traffic will be lighter, it won’t be so hot outside, and so on.
  • It helps wake you up! (Or — if you’re like me — you might be so drowsy that you basically sleepwalk through the whole thing, which isn’t bad either.)

In favor of fed (later in the day) cardio:

  • You don’t have to wake up early. This is a deal maker for me!
  • You might have more energy after getting a meal or two in.
  • It can be a nice way to break up the monotony of a work day.

As you can probably tell, I’m starting to hate fasted cardio. The very idea now makes it harder to get out of bed in the morning. If I get a little coffee and a small meal first, and give my body an hour or two to wake up, I love cardio: I find it relaxing and a great source of stress relief. If you really like to kickstart your day with a brisk walk, go for it! No matter who you are, the best time to do cardio is the time when you will do it, and won’t skip out, make excuses, or find something better to do.

And no, high reps do not count as cardio — even if they feel like they should!

My Cardio Recommendation

If you’re still on the fence, here’s a good protocol for deciding whether you actually benefit from fasted cardio or not. It assumes you’re not doing any cardio, so if you are, you’ll need to take that into account.

  • First: Start out doing 20-30 minutes of low intensity, steady-state (LISS) cardio in a fed state, 2-3 times per week. Stick with that for at least a month, and make careful observations about your bodyweight, your performance in the gym, and how you feel overall.
  • Second: After 4-6 weeks (or when weight loss progress stalls, if that’s your goal), switch to fasted cardio, but stick with the 20-30 minutes of LISS, 2-3 times per week. Again, be consistent with this for at least another month and make careful observations.
  • Third: If you’ve noticed a significant difference between fasted and fed cardio, then great: you have your answer. Otherwise, go back to fed cardio using the same frequency and duration, and stick with that for a while. If, after, another month, you still haven’t noticed any differences, it probably doesn’t matter when you do your cardio — just get it in.
    Fourth: Once you’ve decided when to do your cardio, if your progress stalls, slowly increase either the duration, frequency, or intensity of your sessions to continue losing weight.

It’s not flashy or even much fun, but this kind of slow, logical progress (the same kind I recommend for lifting in my Unf*ck Your Program video series) is the best way to know for sure what works for you!

Editor’s note: This article is an op-ed. The views expressed herein and in the video are the author’s and don’t necessarily reflect the views of BarBend. Claims, assertions, opinions, and quotes have been sourced exclusively by the author.

Feature image from @phdeadlift Instagram page.