Fasted Cardio – How It Works, Benefits, Pros, And Cons

by Charushila Biswas
ISSA Certified Specialist in Fitness & Nutrition

Fasted cardio burns more fat and increases exercise intensity by 21% (1), (2). But what is fasted cardio?

It is exercising without eating anything for at least 6 hours. In other words, fasted cardio is exercising in a fasted state. Heading straight for a morning run after waking up is ‘fasted cardio.’ Here’s everything you need to know about fasted cardio, how it works, benefits, workouts, and dos and don’ts. Keep reading!

What Is Fasted Cardio?

Fasted cardio is exercising without eating for at least 6 hours. It is exercising on an empty stomach (fasted state) without having a pre-workout meal. After 6 hours, you enter the fasting state when the digestive system is empty and is not processing food.

It is scientifically proven that fasted cardio burns more fat compared to cardio done after consuming a meal. But how does that happen? Let’s find out in the next section.

How Fasted Cardio Works?

The way fasted cardio works to reduce body fat is simple. You will source energy to perform cardio workouts from fat rather than carbohydrates. This means you will burn fat, not glucose. Here’s the scientific explanation of how these mechanisms work to reduce the body fat.

When you consume food, the digestive system breaks down complex food molecules into glucose (or sugar), which gets absorbed by the cells. In the cells, mitochondria convert the glucose molecules into usable energy (ATP). This energy is used to perform cardio in the fed state.

If glucose is not readily available, glycogen (stored glucose polymers in muscles) is broken down into glucose and converted into usable energy. What if glycogen is also not available? The stored fat is broken down into free fatty acids. The free fatty acids then undergo fat oxidation in the muscles (because you use muscles to perform exercises) to be used as an energy source.

When you fast overnight, there is no glucose available, and muscle glycogen levels are also depleted. Your body then sources energy by breaking down fat or ‘burning fat’ to fuel the cardio you perform in a fasted state.

Interesting, right? In fact, fasted training also alters the way genes behave. Fasted cardio is a great way to burn fat and reduce body fat percentage. Take a look at the benefits of fasted exercise that are backed by science.

Science-Backed Benefits Of Fasted Cardio

  • Fasted Cardio Reduces Calorie Intake And Burns More Fat

Researchers found that fasted cardio helped reduce calorie intake. The study published in the Journal of Nutrition and Metabolism showed that individuals who had no breakfast before 60 minutes of run in the morning consumed fewer calories in the next 24 hours than those who had breakfast before cardio in the morning (3). Fasted cardio also showed greater fat oxidation rates (fat burn), leading to a greater negative energy balance than fed cardio.

Another study published in the British Journal of Nutrition also concluded that fasted cardio led to greater fat oxidation (4). American scientists have also found that resistance exercise in a fasted state helps metabolize fat instead of carbohydrates. This indicates that fasted cardio can be a great strategy for body weight management (5).

  • Fasted Cardio Improves Glucose Tolerance In A High-Fat Diet

High-fat diets, like the Keto diet, are known for being super effective for weight loss. A study conducted on 18-25-year-old people for 6 weeks showed that endurance training for 4 days per week in fasted state improved whole-body glucose tolerance and Matsuda insulin sensitivity index (6).

This means that they did not experience a spike in blood glucose levels like the people who did fed cardio. Fasted cardio also improved insulin sensitivity, which helped in the uptake of glucose from the blood.

  • Fasted Cardio Improves 24-Hour Fat Oxidation In Women

A study conducted on women showed that 60 minutes of endurance training before breakfast increased 24-hour fat oxidation (7). This means the women continued to burn fat for 24 hours after they performed fasted cardio.

This is how HIIT (High-Intensity Interval Training) works to burn more calories than endurance training. People with knee problems or heart problems can, therefore, perform fasted cardio and push the body in fat-burning mode for the next 24 hours.

  • Fasted Cardio Reduces Body Fat Percentage

Scientists studied the effect of cardio during Ramadan fasting in individuals. They found that people who performed fasted aerobic exercise had a 6.2% decrease in body fat percentage (8).

Fasted cardio is clearly a great way to burn fat, reduce body fat percent and hunger, and improve glucose tolerance in a high-fat diet. Are you ready to jump right in and get started with fasted cardio workouts? Here’s a complete fasted cardio workout regimen. Scroll down.

Fasted Cardio Workouts

Here’s a mix of endurance and high-intensity interval cardio for best results.

  • Warm-up – 10 minutes
  • High knees – 3 sets of 20 reps
  • Rope jumps – 3 sets of 50 reps
  • Jump squats – 3 sets of 12 reps

Rest – 30 seconds

  • Russian twists – 3 sets of 30 reps
  • Leg up crunches – 3 sets of 20 reps
  • Side jackknife – 3 sets of 20 reps

Rest – 45 seconds

  • TRX pull-ups – 3 sets of 12 reps
  • TRX knee tucks – 3 sets of 12 reps
  • TRX abduction – 3 sets of 12 reps

Rest – 60 seconds

  • Skater lunges – 3 sets of 15 reps
  • Burpees – 2 sets of 10 reps
  • Ball slam – 3 sets of 12 reps

Rest – 60 seconds

  • Mountain climbers – 3 sets of 15 reps
  • Planks – 2 sets of 60 seconds hold
  • Alternate plank dips – 2 sets of 10 reps

Rest – 30 seconds

  • Cool down stretches – 5 mins

By the time you finish this routine, you will not only sweat (check out the benefits of sweating), but your “feel good” hormones will also work their magic, and you will begin to feel terrific.

Fasted HIIT Cardio Benefits

HIIT is good because it prevents muscle loss and helps build lean muscle mass. It amps up your workout and keeps you active and agile. There are other benefits of HIIT training:

  • It may increase insulin sensitivity (9).
  • It may prevent you from feeling extremely hungry post-workout (10).
  • It may increase growth hormone levels that aid fat loss (11).
  • It may increase fat-burning chemicals like catecholamine (12).
  • It may increase the metabolic rate for the next 24 hours (7).

Fasted Cardio Results

Not just scientists, but many people around the world are getting good results from fasted cardio. Here’s a video by Briana Shaffer, who tried fasted cardio for a week and got great results. Check it out.

Now, let’s get to the main question – how do you do fasted cardio?

How To Do Fasted Cardio

There are two ways of doing fasted cardio:

  • Exercising in the morning before breakfast
  • Exercising in the evening after fasting for at least 6 hours

But here is something you must know – fasting cardio alone cannot give you the desired results. You must also follow a good diet and a healthy lifestyle to shed that stubborn fat from your arms, thighs, chin, back, and love handles.

Intermittent Fasting And Fasted Cardio

Can you do intermittent fasting and fasted cardio? Yes, absolutely! Intermittent fasting also has many benefits. Break your intermittent fasting after a good 20-30 minutes of endurance or HIIT exercise. Replenish your body with a good protein shake or a protein-loaded meal. Make sure to add high-fiber foods and healthy fats.

Dos And Don’ts

DosDon’ts
Eat after cardio.Do not consume food or meal replacement shakes before cardio.
Drink water.Do not drink sports drinks.
Do a mix of cardio and HIIT for 20-30 minutes.Do not do only HIIT for more than 20 minutes.
Drink a protein shake after a workout.Do not skip the post-workout meal.

There are many benefits of fasted cardio. However, there are a few disadvantages of fasted cardio as well.

Cons Of Fasted Cardio

  • If you are not used to it, you may feel nauseous.
  • If you have hypoglycemia, your blood sugar levels may drop.
  • Fasted cardio, if not combined with HIIT and strength training on other days, along with a high-protein diet, can cause muscle loss.
  • Most research studies conducted are on a small group of people.

Should you try fasted cardio at all? Let’s find out in the next section.

Should You Try Fasted Cardio?

Yes, you can try fasted cardio if you want to burn fat and reduce body fat percentage. However, talk to your doctor and beware of the existing health conditions that may not support fasted cardio. If you are a new mother, avoid fasted cardio.

Conclusion

Fasted cardio is a great way to burn fat fast. With the right type of diet and workout routine, you will start to feel lean and be more energetic and active than before. Talk to your doctor today and get started with fasted cardio to reap all the benefits it has to offer.

Expert’s Answers For Readers’ Questions

  • Is fasted cardio in the morning the best?

Yes, it is best if you practice fasted cardio in the morning after waking up. First, you will be in a fasted state without having to constantly fight hunger or cravings. Second, it will be a great start to your day, and you will be energized instantly.

  • What is the difference between fasted cardio and fed cardio?

Fasted cardio is working out after fasting for at least 6 hours or more without having a pre-workout meal. Fed cardio is working out after having a pre-workout meal. Fasted cardio helps burn fat, while fed cardio burns carbs in the form of glucose.

  • How long after fasted cardio should you eat?

Eat after 15 minutes of fasted cardio. Consume a protein shake or a protein-loaded post-workout meal, along with dietary fiber (fruits or veggies) and healthy fats (nuts, peanut butter, flax seeds, pepita, etc.), to replenish your body with energy and protein.

  • Does fasted cardio burn belly fat?

Yes, you can get rid of belly fat with fasted cardio. Instead of burning the carbs from the pre-workout meal, you will recruit energy from fat sources. As a result, slowly, over time, you will start seeing a reduction in your waist circumference and belly fat. Remember, you must also consume a low-carb diet and healthy foods for weight loss. Keep yourself active and stress-free.

  • Can you drink water before fasted cardio?

Yes, you can drink water before fasted cardio.

  • Can you drink coffee before fasted cardio?

Coffee is a great source of caffeine, which energizes the body and improves exercise performance. You may consume coffee 30 minutes before fasted cardio if you absolutely cannot start your day without it. However, we recommend consuming a glass of water 15 minutes before fasted cardio.

  • Does fasted walking burn fat?

Fasted walking might help you burn fat, depending on the intensity and duration of walking. A slow stroll around the park will probably consume glycogen stores. Walking at 6 mph for at least 30 minutes might burn a little fat. In other words, if you want to burn fat, you must jog or run in a fasted state unless you have a knee injury or have undergone surgery recently.

  • How many minutes should I do fasted cardio?

You can easily get 30-45 minutes of cardio in a fasted state.

  • What should I eat after fasted cardio to lose fat?

Have a protein-rich meal. Try blitzing organic protein sources at home to make healthy protein shakes. You can also consume protein powders. Make sure to balance the high-protein with a good amount of dietary fiber and healthy fats. Avoid junk food and sugary foods.

12 sources

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Charushila Biswas

Charushila Biswas is a Senior Content Writer and an ISSA Certified Specialist in Fitness & Nutrition. She is an alumni of VIT University, Vellore and has worked on transgenic wheat as a part of her Masters dissertation from NRCPB (IARI), New Delhi. After completing her Masters, she developed a passion for nutrition and fitness, which are closely related to human psychology. This prompted her to author a review article in 2015. She has written over 200 articles on Fitness and Nutrition. In her leisure time, Charushila loves to cook and enjoys mobile photography.
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