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How Does the Body Burn Fat? Everything You Need to Know

Connor Sellers
Published by Connor Sellers | Senior Coach
Last updated: August 10, 2023

I’m constantly working both with clients who follow my lead without question and those that ask why before carrying on.

I have found that those who understand the benefits of my training regimens and diet recommendations find it much easier to stay motivated and push themselves.

So, in my opinion, burning fat does not start with dieting; it begins with understanding how the process works. So, I synthesized my knowledge, did some additional research, and compiled all the data that might be useful for beginners to grasp the process of fat-burning.

Let’s dive in.

Quick Summary

  • The body burns fat through a process called calorie deficit, which means consuming less energy than you’re burning.
  • Fat is broken down into carbon dioxide, and water when broken down during weight loss.
  • Water from fat is passed as sweat through the skin, as urine through the kidney, and lungs as carbon dioxide.

How Does the Body Burn Stored Fat?

A woman on a treadmill

Body fat is burned through a process known as creating a calorie deficit, and a good calorie deficit count to start with, according to scientific studies, is 500 [1].

Although the simplistic “calories in, calories out” equation is a bit outdated, to kick start fat loss, you still need to consume less calories than you’re burning.

When the calorie deficit is maintained, fat is released from the fat cell to energy-producing cell organelles known as mitochondria.

It is in the mitochondria where actual fat burning or fat oxidation occurs to produce energy [2].

When you combine diet and exercise, two things happen; The body starts using the energy stored in fat cells and stops putting it away for fat storage.

The byproducts of the fat-burning process, water, and carbon dioxide, are excreted from the human body through urine, sweat, and as you breathe [3].

Now, after the body uses fat cells to extract the energy stored in the form of fatty acids, the fat cells shrink in size but don't disappear entirely.

This means that if you overconsume high-calorie foods in the future, those fat cells will just expand again, and new ones might be created to keep up with the supply, but they can never be destroyed. This is partially why it’s a challenge to maintain fat loss.

The maintenance of the calorie deficit and the continued burning of fat from fat storage results in the reduction of body fat.

What Happens When You Exercise?

When you exercise, your muscles burn stored glycogen for energy. The process takes about 30 minutes to an hour before your body starts burning fat as well. If you’re exercising moderately, it might take longer compared to if you’re on high-intensity workouts.

“After about 30 to 60 minutes of aerobic exercise, your body starts burning mainly fat,”

- Bartolome Burguera M.D, Ph.D. & Chairman of Endocrinology & Metabolism Institute (EMI)

After you go through most of your glycogen stores, the brain signals fat cells to release fatty acids bound in triglyceride form. Both eating fewer calories and exercising causes the human body to release energy stored in the fat tissue.

Experts recommend combining cardio with strength training exercises. Strength training builds muscle, and muscle tissue aids in burning calories. In fact, the muscle is one of the biggest calorie consumers in the body [4].

Related articles: 

Where Does Fat Go When You Lose Weight?

An exercising woman

Fat is broken down into water and carbon dioxide when you lose weight. The carbon is exhaled through breathing while water is excreted as sweat, urine, and exhaled air.

Exercise elevates the disposal of these products through sweating and increased breathing.

As the body continues to burn excess fat, fat cells decrease in size. This is when people start seeing changes in their body composition.

As we’ve mentioned, through releasing fatty acid molecules, the fat cells only shrink in size but don’t disappear.

And when you start consuming too many calories again, the fat cells begin to expand and increase in number to accommodate excess energy.

It might go far and start depositing fat cells on organs such as the liver and muscles [5]. These fat cells are collectively known as “visceral fat”, and this tends to be the most dangerous type of excess fat the body stores.

Related articleWhat Breaks Down Fat In The Body? 


How Does Fat Leave Your Body?

Fat leaves your body after undergoing a series of complex metabolic processes, leaving the fat cell empty. The byproducts of the breakdown are water and carbon dioxide.

The water is passed through the skin when you sweat, through the kidneys when you urinate, and the carbon dioxide is via the lungs when you breathe.

How Do You Know Your Body Is Burning Fat?

You know that your body is burning fat when you start losing appetite, when your clothes fit differently, and when you begin noticing muscle definitions.

Other signs that you’re burning fat include; an improved sense of well-being and changes in the frequency of bathroom visits.

How Do You Get Your Body to Burn Stored Fat?

To get your body to start burning stored fat, start by decreasing your calorie intake to create a calorie deficit, then start exercising or do both simultaneously.

As for exercise, you need to combine strength training and cardio exercises to burn fat to the maximum.

In addition, you need a healthy amount of sleep (7-9 hours) and follow a high protein and fiber diet.

Will You Start Burning More Fat When Dieting?

Evolution has devised complex mechanisms to store and burn fat. But now that you understand the science behind it, it should be easier to take action.

The most important takeaway is what you need to do to start burning fat more efficiently, and that's a calorie deficit, nutritious food, and exercise.

And to help speed up things, I advise all my clients consider taking a high-quality fat burner based on natural ingredients.

Over the years we tested some of the best fat burners which brought excellent results. Here are our recommended supplements:

These are not magic pills, but many proved to be quite effective in our testing, so make sure to check out our guide and see what they can do for you.


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