Is Fasted Cardio Safe? Will It Make You Lose Muscle?

So working out while in a FASTED state (8 – 12+ hours after the last time you ate) is becoming more and more popular. But is fasted cardio, fasted weightlifting etc. SAFE?

People seem to be worried that if they don’t fuel up right before their circuit training or their morning run…they’ll end up feeling light-headed and faint, or something!

But I’m here to tell you the unless you have a pre-existing condition of some kind, it’s 100% safe to work out when your body is in the fasted state, which starts 8 to 12 hours after your last meal. But if you have any concerns about your existing medical condition, PLEASE do ask your doc before attempting fasted cardio or weights!!

Now that that’s out of the way: if you do work out while fasted, are there any considerations or stipulations at all?

Well, yes, and that’s why I wanted to write this article. Not only for people who are considering fasted cardio as a way of burning fat, increasing metabolism, making insulin sensitivity better, taking advantage of that burst of human growth hormone that happens in the fasted state…oh yeah, and something you may not have thought of, reducing the risk of the dreaded stomach cramps while running or doing other cardio!!

But I also wanted to write this post as a very mild warning to people who are already doing fasted cardio, and maybe haven’t done all the research ahead of time: It IS important that you don’t go too long and too hard because muscle loss can occur if you really overdo it.

According to fitness trainer Thomas DeLauer, if you go at a higher intensity than 65% of your max heart rate, or if you work out for a long time (like a run that’s longer than 45 minutes), then you hit a point where you risk losing muscle during these fasted workouts.

However, I don’t think this is as much of an issue as some people might make it out to be, if they’re trying to argue against doing fasted cardio. Because as anyone who’s done it can tell you, your body will pretty much tell you when to quit. 😉 So this is only a concern for people who routinely ignore their body’s cries to STOP. I know they say to push it to the limit, but if you’re starting to feel light-headed and dizzy, please remember THAT is indeed the limit!

Another thing you may want to consider if you get extra hungry on a fasted run: you can try a BCAA supplement and or sipping a drink with electrolytes before the run, in order to still get the benefits of the fasted state, while also replenishing some of your body’s vital nutrients!

A good electrolyte balance will make sure you don’t get cramps, which like I said earlier, is supposed to be one of the big pluses of fasted cardio!

I know you’re thinking, won’t those supplements break my fast, and the answer is, the types of people who worry about what will and will not break their fast to that extent that they would turn down BCAAs, Himalayan pink salt, and other very low calorie supplements are the ones who are doing intermittent fasting for the cell regrowth benefits, but taking supplements that are sugar/carb free, and below 50 calories, won’t break your fast for the purposes of fat burning!

A lot of running experts recommend working out in a semi-fasted state, by drinking your pre-workout. Energize Lemon is my favorite pre-workout because it’s got beta-alanine to prevent lactic acid buildup and increase muscle POWER, plus it actually tastes great!


So my recommendation, if you’re worried fasted cardio will make you feel ill or dizzy or whatever…still give it a try, of course making sure that your last meal was full of healthy fats so that your body will be able to utilize that fat for energy!!

Experiment with fasted and semi fasted cardio. See what works best for you. And in the end, it’s still OK if you feel your best with a meal shortly before your workout. But not too shortly before!! 😉

About the Author Melissa McAllister

Leave a Comment:

2 comments
Yeimi Martinez villarreal says May 11, 2019

I want to tone and loss my belly fat and tone my body

Reply
Jessica says May 13, 2019

Wow Melissa,

You really answered one of the questions I’ve wondered for a long time: whether or not drinking Energize/BCAAs would break my fast. Awesome material, thank you!

Reply
Add Your Reply