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Should You Be Doing Fasted Cardio?

  Published on November 5th, 2021
  Reading time: 4 minutes
  Last modified July 7th, 2023
Women doing fasted cardio

You may be familiar with intermittent fasting and how it can help you maintain the metabolic state of ketosis, but there is an increasing buzz around a different type of fasting. Fasted cardio is a technique that takes weight loss and fitness goals up a notch but like with anything, it may (or may not) be right for you. The exercise strategy of working out before breaking your overnight fast was formerly commonplace only in the world of competitive athletes, but now it’s growing in popularity even for the average gym-goer, jogger, or Yogi. When fasting is paired with the ketogenic diet, it may expedite your health and wellness results.

What Is Fasted Cardio?

Simply put, fasted cardio means you’re getting cardiovascular exercise before you have your first meal of the day. While the semantics can be misleading, any type of workout routine (not just running or spinning) where your heart rate is elevated can be considered as fasted cardio—this includes most forms of exercise.  

It’s recommended to do your fasted exercise right when you wake up, after having fasted overnight, between seven and 12 hours. A fasted state can take between three and six hours to occur after your last meal–the rate at which it occurs depends on the amount of food consumed.

After several hours, your body has processed all food, insulin levels are low, and you have depleted your glycogen stores so you will use fat for energy, which, as you know, is quintessentially keto.

In this fasted state, your workout routine probably should not exceed an hour in duration. Be sure to consistently hydrate with water and then replenish with food upon completion, even before you hit the shower!  

Is Fasted Cardio Right for Me?

As with any other nutrition or fitness technique, fasted cardio may be suitable for some, but not for others. Have you ever had a cup of coffee and then headed out the door for a run? That’s cardio in a fasted state. Do you sometimes feel bogged down after breakfast, so you have transitioned to doing yoga after only having had a morning bottle of water? Also fasted cardio.

Running while fasting on keto

Some genuinely feel better when working out on an empty stomach, while others need a bit more fuel in their systems—in other words, it’s not for everyone. Potential candidates for fasted cardio are in generally good health, maintain proper nutrition, and get adequate rest. If you’re uncertain if fasted cardio is a good fit or if you identify with any of the following conditions, it is best to speak to your doctor:

  • Low blood pressure
  • Diabetes
  • Adrenal-related issues

Of course, if you are pregnant or breastfeeding, under the age of 18, or have had eating disorder tendencies, fasted cardio should likely be avoided.

Benefits of Exercising While Fasted

Your body’s reaction to exercising while fasted will be influenced by age, activity level, genetics (to some degree), and body type so the benefits may differ between individuals.

Keep in mind, not everyone feels up to putting in the work when void of a hearty breakfast. This could result in a lackluster workout where no advantages will be reaped, so experimentation with fasted cardio may be required to see if you, too, will experience documented benefits.

Fasting, Cardio, and Keto for Fat Loss

Exercising while fasted helps your body tap into stored body fat for energy. When following the keto diet, this process is even more efficient since your body is not required to get through any excess glycogen stores—it burns fat right away!

Studies have shown that abdominal area blood flow increases when you’re in a fasted state. This can assist with burning fat cells that are stored in the midsection. [1]

An added benefit, fasted cardio helps you get back into ketosis if you happen to go over on your carbohydrate and sugar limits.

Exercise Efficiency

Black coffee fasting and exercise

It sounds quite optimistic to get up early enough before work to prepare breakfast, let it digest, and then hit the gym. And let’s face it, after a full day of work, working out can sound less than appealing.

Fasted cardio makes morning workouts far timelier—you get up, hydrate and caffeinate without added sweeteners (if you choose) and get to it.

Some people note feeling lighter on their feet, more agile, and even faster when getting their cardio in before breaking the fast.  

Like most nutrition- and fitness-related tactics, fasted cardio can be beneficial and suitable if conducted in a reasonable fashion. If you have tested this type of cardio and it doesn’t feel right for you, a fed state is probably your best bet.

Warning signs to look for are dizziness, lightheadedness, confusion, shakiness, and weakness—these symptoms could be related to low blood sugar or dehydration. As always, listen to your body and do not proceed if any of these feelings should occur.

Aimee Aristotelous, author of The 30-Day Keto Plan, Almost Keto, Super Simple Keto, The Whole Food Pregnancy Plan, and The Doctors Weight Loss Diet is a certified nutritionist, specializing in ketogenic and gluten-free nutrition. Her expertise has been featured in Health, People, HuffPost, Parade, Yahoo!, INSIDER, Motherly, Consumer Health Digest, Simply Gluten-Free, Well + Good, and the National Celiac Association. Aimee resides in Fort Lauderdale, Florida, with her husband and son, and enjoys cooking, working out, wine tasting, and traveling.



Gjedsted J, Gormsen LC, Nielsen S, Schmitz O, Djurhuus CB, Keiding S, Ørskov H, Tønnesen E, Møller N. Effects of a 3-day fast on regional lipid and glucose metabolism in human skeletal muscle and adipose tissue. Acta Physiol (Oxf). 2007 Nov;191(3):205-16. doi: 10.1111/j.1748-1716.2007.01740.x. Epub 2007 Sep 3. PMID: 17784905.

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