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By: Heather Marr

Heather Marr is an N.Y.C.-based personal trainer and The Model Trainer Method creator, whose A-list client roster includes some of the world’s most famous supermodels. Ahead, she writes about the benefits of fasted cardio.

Fasted cardio simply means performing your cardiovascular workout without eating beforehand. The window of time between your last meal and the start of your workout would depend on factors like the quantity and quality of your last meal and how quickly you digest that fuel. Many people wake up in the morning and head straight to the gym for fasted cardio but it’s also an option for those who enjoy intermittent fasting as well. As with anything, arguments can be made for and against performing cardio in an unfed state. 

Throughout my teens and most of my 20s, I performed daily fasted cardio, usually running 10-15km at a moderate pace. This was extremely convenient for my lifestyle at the time. I was able to sleep in as late as possible and head straight to the gym. I was training at a moderate pace, which is preferable to use fat for energy. My workouts were short enough that I wasn't hitting a wall without eating first. There are studies that show when moderate cardio is performed fasted, the body uses its own fat to fuel the activity. That alone has turned some former fans of evening exercise into early risers.

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The issue with performing cardio in an unfed state is that the body may breakdown the protein in muscle to fuel the activity. So, if I'm trying to add or conserve lean mass, this might not be the best choice depending on how I choose to approach programming. The other issue is that training intensity and duration will, of course, be affected. This makes certain types of activities better choices than others to be performed in a fasted state. A slow, steady jog is preferable to sprints and an incline walk is preferable to weight lifting.

what is fasted cardio

The Benefits of Fasted Cardio

When we look at lowering body fat, we know that we need to create a deficit through training and nutrition for our body to use its fat. The most important factor here for most people in many cases is looking at overall numbers throughout the day. If I am able to train harder and longer after eating rather than before eating, then my overall expended energy, both during the activity and throughout the day, even after completing the exercise is going to be higher. Assuming that I spread out my macros and fuel throughout the day without compensating for the additional activity, I'm going to lose more weight.

What to Eat After Fasted Cardio

Is fasted cardio better than cardio in a fed state? The answer is not black and white. Certain lifestyle preferences and activities lend themselves better to those that do choose to train before eating. Moderate cardio such as swimming, walking, and jogging are better choices for an unfed state versus intense activity such as HIIT or weight training. For those who do choose to train before eating, it is important to have fuel on hand with you to consume after exercising. Great options include a whey isolate shake with fruit, whole wheat toast and egg whites, and overnight protein oats.

But the most important thing is finding a way to fit activity into our lives consistently in a way that works for us whether that be in a fasted or fed state.