Science Explains Where All That Lost Fat Goes

by Dr. Ahmed Zayed
Published on April 15, 2020
man in gray hoodie

For anyone who has dreamt of getting a toned, lean body, here is a little secret – You need to focus on one thing, and one thing only – fat loss. Fat loss will help you to forget all about your round belly, your bulky legs, and finally get an hourglass body figure that you have always wanted. 

But have you ever thought about where all that lost fat goes? How does your body lose fat? We will let you on yet another little secret – That lost fat exists our body. The mechanism is not like anything we have thought before, as it seems that many researchers have got it all wrong. Now, science has come yet again to fix the mistakes from the past, offering us some facts as to where the lost fat goes as soon as it exits the fat cells in the body.

Why is it important to lose fat?

While many of us focus on fat loss as a self-confidence boosting mechanism that we have developed over the years, our body image and self-esteem are not the only ones that are meant to benefit from this entire experience. Fat loss will reflect positively on our entire physical and mental health and overall well-being, that is. 

Obesity is defined as a condition in which the person has a harmful amount of body fat and/or unhealthy distribution of body fat, usually around the abdominal area, especially among women. For an individual to be declared obese, their BMI (Body Mass Index) needs to be as high as 30 or higher (1).

Besides being defined as a definite condition, obesity is also being defined as an enormous health risk, bringing us closer to multiple health issues. This list would include diabetes type 2, heart disease, heart attack, stroke, depression, anxiety, high cholesterol levels, high triglycerides levels, high blood sugar levels, etc. (2, 3).

So, if you are not in it for the benefit of your self-confidence, then perhaps you would consider adapting to a healthier lifestyle for the benefit of the overall health of both the body and mind. Let’s see how exactly fat loss works, shall we?

How does weight gain work?

Before we dive into the more complicated mechanisms of action, let’s cover the basics first. How about starting with covering why we gain weight? This is pretty simple, is it not? Our body needs energy – energy that we are providing through food. For many people, the whole process of determining how many calories do their bodies need and later properly satisfying that very same number seems tricky; thus, many of them end up overweight or obese. 

When we intake excess calories, day after day, we start gaining weight. What happens is the extra consumed energy, usually in the form of carbs and fats, is being stored in the fat cells like triglycerides. Storing this extra energy is the body’s way of making sure that there will always be enough energy for it to complete the everyday activities if we happen to fail to provide the needed number of calories (4, 5).

However, if we keep storing extra energy, without eventually using it, our body is creating a fat surplus. It is this fat surplus that brings us closer to the long list of serious health issues that we mentioned earlier. And it is this very same fat surplus that we want to see getting eliminated when we are trying to lose weight, or fat, to be more precise. 

How does fat loss work?

Our body uses three compounds as an energy source with that being carbs, fats, and last protein in that exact order. Carbs are the first to go when we need energy. Next in line are fats, whereas protein is considered to be more important since it has an essential role in our body. That is why only a small amount of protein is burned during exercise, leaving the rest of it to help our sore and tired muscles to recover, rest, and grow afterward (6, 7, 8, 9).

One general rule that you may need to respect when trying to lose weight is a calorie deficit. Weight loss is all about acknowledging the number of calories that your body needs to maintain your current weight is. This number is based on different factors such as weight, height, physical activity, age, sex, etc. 

Once you determine this number, you may need to cut it down by at least 500 calories to help your body burn fat sustainably and effectively. This is what we like to call a calorie deficit. A daily-500 calorie deficit is a good place to start if you are new to all of this. Note that this number variates from person to person, and it may require some adjustments, as you see fit.

When you reduce your usual daily calorie intake, your body will have no other choice but to dip into that fat storage within your fat cells that we mentioned, to make sure that there is enough energy for every single cell inside of it. The stored fats will become the source of energy that your body relies on (10).

So now that our body will focus on the stored fats and starts to see this storage as a primary energy source, it will focus on releasing those very same fats from within the fat cells. The next step involves the fat cells being transported to the body’s very own energy-producing machinery that you may have heard being referred to as the mitochondria. A series of complicated processes take place that eventually presents our body the ultimate result – energy. 

Continuing the calorie deficit will help things progress and help you lose more fat than ever. You will start noticing as your body is changing. It will start getting toned and lean, and you will notice other positive effects as well. Your mood will improve, you will sleep better, you will have more energy, and overall feel better in your skin.

Where does all that lost fat go in the end?

Let’s be honest – many of us are just happy to see the numbers on that scale going down, not exactly what happens to all of that lost fat in the process, right? Well, whatever the case may be, you may be curious to find out that the lost fat does not magically disappear. There is no such thing as magic, and no matter how mystical our body may seem to you, there is still no magic involved. Everything about fat metabolism can be explained with the help of science. 

A couple of misconceptions regarding fat loss have presented to the public over the years. For what seems the longest time ever, people seemed to think that the lost fat would turn into either muscle or would escape through the colon. 

But it was not only the public that had made a mistake believing and following these misconceptions – it turns out that doctors and even researchers from all around the world seemed to have mistaken about the fat metabolism of our bodies. That is what the physicist Ruben Meerman explained in his research called “When somebody loses weight, where does the fat go?”, published back in 2014 (11).

He talked about how many medical professionals are not exactly aware or fail to understand fat metabolism on a molecular level. And what is exactly what he did – he described the final products that we are presented with as the result of the fat metabolism process. 

It may sound surprising enough to learn that almost everything that we eat at the end comes out through our lungs. That, what is left of it, comes out through the water. This rule applies for any fats, carbs, protein, and again – surprising enough – even alcohol. As Ruben Meerman proceeds to explain, 84 percent of the lost fat is exhaled in the air in the form of carbon dioxide, whereas the remaining 16 percent is excreted in the form of water through urine. 

Water and carbon dioxide are the two most common byproducts of our daily metabolism. At the end of the day, it is through urine, perspiration, and exhalation that our body makes sure that there is no waste left inside our body. It seems that it is our lungs that are marked as the primary organ used to remove any excess fat from our bodies. 

But do not get mistaken here. Just because we pointed out that the lungs are the ones that you may need to say “thank you,” breathing at a faster, than normal, the rate will not get you any slimmer if you do not put in the hard work. This is certainly not an effective, nor a recommended method. This can only cause you to hyperventilate, feel dizzy, and even lose consciousness. 

Tips on how to lose fat in an effective and sustainable way

So, if breathing at a fast rate alone will not do the trick, then what is? Weight loss, and fat loss, for that matter, have always been more complicated than that. There is not an easy way out of all of those extra extra pounds and layers of fat around your belly. Although some people may have it easier, thanks to their genetics, all of us have to work hard if we want weight loss results that are here to stay. 

Adapting to a calorie deficit is a good start, as we mentioned earlier. Now next, you will also need to work towards improving your metabolic rate. So, not only will you be eating fewer calories, but you will also stimulate your body to burn more as well. The best way to do so is through regular physical activity. 

Regular physical activity will get you plenty of beneficial effects for your overall health as well, the same way that losing that extra weight and fat will do. As the experts working at The American College of Sports Medicine (ACSM) suggest, the recommended amount of physical activity weekly is around 150-minutes of moderate-intensity exercise (13, 14).

There are many ways in which you can be more active, including home workouts, running, yoga class, swimming, and even taking the stairs instead of the elevator will help your body burn more of that stored fat. Any physical activity that will get you off the couch and into some workout clothes is welcomed. 

Now pair your new workout routine with a well-balanced diet and many water, and there you have it – the combination that will get you to lose weight and fat like never before. Make sure that you eat many fresh fruits and veggies since they are highly nutritious and low in calories. They will keep you full for a longer time and help you lose weight without having to starve yourself. 

Next, we have a protein that you may need to include in each of your meals and even snacks. Water is very important, as well. It has been scientifically proven that drinking water before the main meal will help you to reduce the number of calories that you will intake. The same goes for eating a salad or some tasty soup before a meal as well (15). 

You see, it is all about small, yet meaningful steps that you may need to take if you want to change the way that you see yourself. A healthy lifestyle is what will get you to lose those stubborn extra extra pounds once and for all.


In today’s article, we focused on finding out where does all that lost fat ends up when we figure out that we have seen a satisfactory change in the number shown on the scale. It seems that unlike previous beliefs, the lost fats do not get converted into muscle, nor do they escape through our colon. It is thanks to our lungs and kidneys that we can say goodbye to all of that extra fat and focus on getting the body of our dreams!


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