Check out the chiseled physique of any runner, HIIT exercise enthusiast, or biker and you can clearly see that cardio is an effective fat burner. We hear it all the time – cardio can kick start fat and calorie burn. But have you ever stopped to think how?
As a nutrition nerd and fitness freak, I love sneaking into the science behind how things work.
So how does cardio burn fat? The research from over five studies suggests that cardio burns fat through calorie expenditure and is mainly excreted through gases via the lungs. The most effective way to burn fat is through a mix of high-intensity interval training (HIIT) and weight training. And as for fasted cardio, it depends on the individual.
Let’s get a sprinting start on how heart pumping cardio burns fat.
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How Does Cardio Burn Fat? Research From 5+ Studies
Did you know that despite decades of research on the impact of exercise on fat burn, it’s still not fully understood how exercise helps regulate fat? Meaning there are many other factors to consider, such as your genetics and nutrition, when it comes to your body composition.
However, it is understood that exercise improves the ability of our muscles to oxidize (break down) fat. It does so by burning calories and expending byproducts via the breath. We’ll also cover the science behind a few different cardio burning techniques including fasted cardio and high-intensity training to get you on the fat burning track.
Cardio Burns Calories (And Therefore Fat)
One of the main ways that cardio can help burn fat is through burning calories.
Weight and fat loss happens when you create a calorie deficit, meaning you burn more calories than you eat. This can be done by reducing calories that come from food, but the healthiest way to do it is by combining it with cardio, strength training, and a healthy diet.
METABOLISM AND CALORIE BALANCE
Your body requires energy to do basic functions such as your heart beat, breath, and repairing cells. It does this at rest and automatically. This is called your basal metabolic rate (BMR).
Your BMR is influenced by factors such as your body size, muscle mass, sex, and age. There are also “behind the scenes” factors such as your genetics, gut bacteria, and hormones that come into play.
On top of this, you have your activity burn. This is where cardio and other forms of activity come into play. This can include energy that’s needed to break down and absorb the food you eat, energy needed to do daily activities such as moving at work, and physical fitness.
Physical activity calorie burn depends on the type, intensity and duration of the workout. When your goal is to burn fat, regular, frequent, and intense exercise will be your best bet.
Related Article: Can Cardio Burn Muscle? (Yes, Here’s How)
CARDIO FOR CALORIE BURN
Cardio is one of the most efficient calorie burners, especially something at a higher intensity, such as fast paced running. According to Harvard Health, running can burn as much as 539 calories in 30 minutes when running at an 8.6 miles per hour rate.
Studies suggest that running can actually regulate appetite hormones better than walking. Meaning that when you run, it’s more likely that you’ll burn more than you eat when compared to walking.
Keep in mind that your body may burn calories differently than others. A good way to check how many you burn is through the Health Status automatic calorie calculator: Calories burned.
GENERAL CARDIO RECOMMENDATIONS FOR WEIGHT LOSS
If your goal is to burn fat or lose weight, this can vary depending on your body. As the Centers for Disease Control (CDC) explains, the calorie balance needed to maintain or lose weight is very individual. Some people will need to be more active in order to create that negative (expending more than eating) calorie balance.
The U.S. Department of Health and Human Services provides a general recommendation that you should get at least 150 to 300 minutes of moderate-intensity exercise or 75 to 150 minutes of vigorous-intensity exercise per week in order to see changes.
Related Article: How To Lose 5lbs In A Month (The Healthy Way)
How Is Fat Burned?
So cardio can help burn fat, but where does it go when you lose it?
First off, it’s important to understand how fat is stored. When we eat extra carbohydrates and proteins in the diet, they are converted to triglycerides and stored as fat. Dietary fat doesn’t need this conversation. When you try to lose weight while maintaining your muscle, you are attempting to metabolise (break down and use) the triglycerides stored in your fat cells.
Contrary to popular belief, fat is not lost through energy conversation or heat. Nor is it excreted through feces or converted to muscle.
Research shows that the lungs are the primary organ for excreting the byproducts of weight loss. Fat is converted into carbon dioxide and water. In fact, most carbs, protein and alcohol we consume is also changed into water and carbon dioxide as well. The water gets excreted in the urine, feces, sweat, breath, teats, and other body fluids.
To expend more fat through the lungs, we have to use muscles so they use more oxygen and switch to fat burning. During light aerobic exercise or short workouts, your body uses glycogen (stored glucose energy). Once it’s used up, then the fat metabolism is activated.
Learn more about glycogen here: What To Eat After Fasted Cardio (5 Things To Know)
The Best Cardio To Burn Fat: HIIT
Research states that the effect of regular aerobic exercise on body fat is negligible but certain forms can have a bigger impact on body composition.
Two types of physical training include aerobic and anaerobic. Aerobic training requires the presence of oxygen. This is the type of exercise done at a sustainable pace for an extended period of time. Examples include light jogging, biking, or swimming.
It’s also called, low-intensity steady-state (LISS) exercise. It usually takes about 30-60 minutes and the lower in intensity doesn’t burn as much fat and calories than higher intensity cardio. That’s not to say it isn’t a good form of exercise, but when it comes to fat burn, anaerobic activity is where the money’s at.
Anaerobic exercise does not require the presence of oxygen. This includes exercise such as sprinting all out or using heavy weights until you can’t go any more. This type of exercise is not sustainable for long periods of time.
Related Article: Are Squats Cardio Or Strength Training?
WHAT IS HIIT?
High-intensity interval training (HIIT) includes intervals of very hard work, to the point where you cannot go for more. It’s a cardio exercise that lasts from six seconds to a couple of minutes, then has six seconds to a couple minutes of rest time. The intervals are repeated.
The intense exercise portion can last anywhere from 15 seconds to a few minutes. A typical HIIT workout has 5-8 exercises performed for 30-60 seconds each, alternating with 20-30 second rest periods.
HIIT can include any type of cardio such as biking, jumping, or sprinting. There different types of HIIT based off of timing. Such as Tabata workouts which are 20 seconds at max capacity, then resting for 10 seconds, then repeating for another 20 seconds; for eight rounds or four minutes in total. HIIT can also be done with weights.
HOW HIIT BURNS FAT
Due to HIIT’s intensity, it can burn more calories in a quicker amount of time. Research has found that HIIT burns about 25-30% more calories than other types of exercise. One study found that individuals can burn more calories performing HIIT than spending the same amount of time doing steady-state exercise.
HIIT not only burns calories during the exercise. It also scorches calories after the exercise.
In one study, women completed either aerobic exercise, HIIT, or resistance training. They were given carbohydrates and protein to see how effectively their bodies burned energy. Then their resting metabolic rates were measured right after the exercise, 30 minutes after the exercise, and 60 minutes after the exercise. HIIT produced the greatest post-exercise burn.
Post-Exercise Burn: EPOC
Once a workout is over, your metabolism can continue to burn calories even when you’re not doing anything. As defined by the American Council on Exercise (ACE), excess post-exercise oxygen consumption (EPOC) is the amount of oxygen required to bring the body back to normal, resting level of metabolic function.
HIIT is the most efficient way to stimulate the EPOC effect. During the EPOC period, the body uses oxygen to restore muscle glycogen and rebuild muscle proteins that were damaged during the exercise. Even after the workout, the body continues to use aerobic energy pathways to replace the energy and fuel, therefore increasing calorie burn.
HIIT also helps lower insulin resistance. This is when cells in your muscles, fat and liver don’t respond well to insulin, therefore you produce more insulin which stores fat. Suppression of insulin secretion and improvement of insulin resistance is associated with a loss of body weight and fat mass.
GIVE HIIT A GO
Choose three cardio exercises such as running in place, jumping jacks, and jump rope. Do each one for one minute, with 30 seconds of rest in between. Go as hard as you can with good form, then rest. Go for as many rounds as you have energy for. Don’t forget the warm up and cool down.
Fitbod announces: HIIT is here!
What About Weights?
Although cardio is an excellent way to burn calories and fat, studies show that resistance training will have a greater impact throughout the day. So basically you’ll continue to burn calories after picking up those weights.
Resistance training is an exercise that causes your muscles to contract against resistance, in order to increase strength, muscle build, or power. This can be done with hand weights, dumbbells, your own body weight, or exercise bands.
When you lose weight, through means of calorie scorching exercise and a healthy diet, you generally lose both fat and muscle. If you don’t include resistance training in your exercise routine, you could potentially slow down your metabolism since you’re losing that lean muscle.
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Mayoclinic recommends resistance training at least twice a week to help counteract muscle loss which is associated with aging. They also explain that since muscle tissue burns more calories than fat tissue at rest, muscle mass is a key factor in weight loss.
Not sure where to start? Try this out: How To Start Strength Training With Dumbbells Only (Ultimate Guide)
Is Fasted Cardio, Faster For Burning Fat?
Just like the name implies, fasted cardio is a form of cardio done while fasting. It’s usually done in the morning since your body has had all night to use up stored energy. The idea about hitting up a cardio sweat sesh first thing in the morning (or after about six hours or more of not eating) is that since the glycogen (stored carb energy) is already used up, your body will burn fat as fuel.
Current research suggests that training in a fasted state does not burn more fat than performing cardio in a fed state. One small study found that twenty healthy young females showed no significant difference in fat burn. However, research seems to be inconclusive.
More research is needed when it comes to the post exercise effect of fat burn from fasted cardio. It appears that fasted cardio can improve the ability of muscles to burn fat during the exercise but the overall benefits are not significant, unless it’s used to promote ketosis.
Something to consider is that when you wake up in the morning, cortisol (stress hormone) is naturally elevated to help you get up. For some people who exercise without eating, it can lead to stress on the body and elevated cortisol. Cortisol has been linked to more abdominal fat storage.
So whether or not you choose to do fasted cardio can be based on how you feel. If you prefer to not eat before your cardio workout, just make sure to eat within an hour after the workout. Focus on a combination of protein and carbohydrate in order to promote muscle growth and replenish lost fuel stores.
Check out some healthy protein and carbohydrate combinations here: What To Eat After Fasted Cardio (5 Things To Know)
Too Much Of A Good Thing
Even hearing that cardio burns fat can motivate you to grab your running shoes and run until the pounds melt away. But going too hard and doing too much can be bad for your health and prevent the results you’re looking for. This is especially true for types like HIIT.
When you overtrain, it can increase inflammation, the stress hormone cortisol, and cause your metabolism to decrease since your body goes into preservation mode. All of these factors can get in the way of results.
Chronic inflammation may contribute to some diseases and weight gain. Research shows that regular exercise reduces inflammation. However, if you’re hitting it too hard, inflammation can remain high.
Cortisol is known as the stress hormone. High levels of cortisol can cause fat stores, especially relocated in the abdomen. When left unchecked, this can enhance weight gain even further. Research shows that moderate to high intensity exercise can increase circulating cortisol levels.
IMPORTANCE OF EATING ENOUGH
If you don’t eat enough, especially when pumping up the cardio, it can actually prevent you from burning fat. Your body is designed to keep you from starving. So if you don’t give it enough calories to perform its basic functions and activity, it will drop your calorie burn level in order to make up for this. When your metabolism is slow, you burn less calories and are more likely to hold onto excess fat.
Check this out to make sure you’re eating enough: calculate your calories.
Final Thoughts: Don’t Forget to Mix It Up
Cardio is not required in order to lose weight and burn fat. You can lose fat by creating a calorie deficit (taking in less calories than you expend) and by also doing resistance training. However, cardio exercise can help create this deficit in calories, therefore aiding in the weight loss effort.
It’s important to do a variety of exercises to prevent your body from getting used to a routine. When your body adapts to exercise, the caloric burn will gradually decrease. Switch up your exercise every three months or so to keep up the fat burn.
If you’re new to exercise, ease into it and find things that you enjoy and keep you motivated. And always make sure to contact your physician before starting a new fitness routine.
Ready for step-by-step instructions for how to start burning fat? Download the Fitbod app today.
About The Author
Lisa is a registered dietitian nutritionist (RDN) with over 15 years of experience in nutrition, fitness, and mental health coaching and education. She studied Foods and Nutrition at San Diego State University and earned a Master of Science in Holistic Nutrition at Hawthorn University.
Having certifications and experience in group exercise, intuitive eating, coaching and psychotherapy, and digestive wellness, she’s enthusiastic about the relationship between the body and mind.
She’s dedicated to helping people understand how to implement healthy habit change, while gaining a deeper understanding of what makes them feel their personal best.