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Where Does Fat Go When Losing Weight?
According to Science

Isaac Robertson
Published by Isaac Robertson
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: August 16, 2021

There are so many misconceptions around what actually happens to fat, and it’s a question personal trainers often encounter by people on their weight loss journey.

Fat metabolism is a notoriously confusing concept, and when we asked some readers, respondents thought fat turns into muscle mass.

So, to help put an end to big fat myths, we teamed up with a physiologist to give us the details of what really happens to body fat cells.

How Does Fat Leave The Body When You Lose Weight?

person pinching her belly with her hands

The correct answer to this question is that most body fat cells break down into carbon dioxide and water.

But it’s a bit more complicated than that.

To better understand what happens to white adipose tissue, it’s important to take a full look at all the things going into and out of your body.

First of all, you take in food and drink in the form of fat, protein, carbs, dietary fiber [1], and water. And then there’s oxygen that you have to account for as well.

“Fibre, on the other hand, passes through into the colon undigested, where it adds bulk to stool and, in some cases, becomes food for the beneficial bacteria colonizing the gut.” - Canadian Society Of Intestinal Research. 

The body then processes all those substances, breaking them down, transforming them; additionally, it generates heat and energy in the process.

But the law of conservation dictates that the amount of matter in total has to stay the same, which all chemical reactions obey.

Now, if more stuff goes into your body than comes out, you’ll experience weight gain and a change in body composition.

And nearly all the weight you gain ultimately ends up in fat stores.

One other mistake people make is that the reverse process of burning fat and rapid weight loss means that fatty tissue somehow ends up back in your bowels to be removed.

However, nearly all the fats break down into carbon and water, and they leave the body by breathing out carbon dioxide and urinating or sweating water.

How Does Fat Metabolism Work?

woman with a fork in her mouth and holding her stomach

Understanding fat metabolism is one of the best ways to ensure that you don’t fall into the trap of weight loss and weight regain, i.e., that dreaded yo-yo effect.

Resting Metabolic Rate

Let’s start with your base metabolic activity [2]. This is the energy needed to keep your heart beating, lungs pumping, organs working, and brain thinking.

At this rate, there is very little change in blood flow, and your body burns calories just to stay alive.

Even with little more activity than moving from bed to your desk, to the couch, and back to bed, you won’t necessarily experience weight regain.

However, all health professionals will recommend that you adopt healthy habits that bring a lot more activity.

But if you consume fewer calories than you burn, then you will ultimately lose adipose tissue.

And it’s a lot easier, though, with a more active metabolism.

Active Metabolic Rate

You can impact your body fat distribution even with moderate-intensity resistance training. As long as you avoid excess energy intake, that added physical activity would require more calories.

And if you have a calorie deficit diet, your body has to metabolize other energy sources.

It’ll either look for more macronutrients from food or eventually target fatty tissue and help you lose weight.

Does Your Body Process Fat When Dieting?

woman holding up a glass of water and a salad bowl

I hate to have to answer that question this way, but it depends.

If you’re going through fad diets or limit your calorie intake but still eat loads of junk food and sugary treats, then your digestive system will still process all your food causing blood sugar spikes, and you’ll end up with the same fate as overeating.

This is what I tell all my clients: you can’t out-train a bad diet.

Fat cells shrink when you have a healthy balanced diet that keeps a careful eye on your daily target calories to produce a 10% to 20% net-negative calorie intake.

It’s the most important factor and the only thing that will help you lose weight.

And maintaining weight loss will mean that your energy input equals energy output to keep a stable metabolic rate.

Related: 5 Best Diets for Burning Body Fat

Does Exercise Burn Body Fat Cells?

shirtless man doing mountain climbers at home

Yes, exercise plays a role when it comes to removing body fat cells, but only as a way to boost how much energy you burn.

Every form of physical activity will trigger metabolic responses, but if your body has plenty of simple carbs in reserves, then you’ll find it very difficult to lose weight successfully.

But assuming that you have fixed your diet as mentioned above, then taking care of your fitness needs will force your body to produce energy from other sources.

And ultimately, that will have to be stored fat reserves.

As mentioned above, breaking down those flabby cells releases energy, and most of the remaining matter exits your body through sweat, urine, and carbon dioxide.

Most dietitians and fitness coaches will agree that you need to focus 70% of your attention on a diet and 30% on exercising to successfully lose weight.

FAQs

Which Part Of the Body Loses Fat First?

The hard fat around organs is the first part of the body to lose fat. It’s possibly the most important fat to lose as it can negatively impact the functioning of those organs.

After that, the body will start to remove soft fat under the skin.

What Is the Hardest Place to Lose Fat?

The hips, thighs, and belly are the hardest places to lose fat. It’s one of the biggest frustrations of weight loss and comes down to the fact that fat in other parts of the body is more easily accessible.

Now You Know What Happens During Weight Loss

The simplest way to look at it is that the body will transform fat into carbon and water, and you’ll exhale most of the carbon as carbon dioxide and sweat or urinate the water.

It’s an amazingly effective process and so common for people to not fully understand the importance of physical activity, higher oxygen requirements, and breathing out carbon dioxide.

Ultimately, the only way to achieve fat loss will come down to fixing your diet to avoid the permanent yo-yo effect: you lose weight, you gain weight, and don't seem to get anywhere.

Check out all of our weight loss guides and training and diet recommendations to see how you can make the best possible changes, and don’t forget to share your thoughts in the comments below.


References:

  1. https://badgut.org/information-centre/health-nutrition/dietary-fibre/
  2. https://www.active.com/fitness/calculators/bmr

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