How Does Fat Leave The Body During Weight Loss 2023?

Reviewed by Dr. Drew Sutton, MD

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how does fat leave the body
Fat leaves the body in the form of carbon dioxide and water. Photo: Shutterstock

If you joined a weight loss program, you might be curious to know how fat leaves the body when you start losing weight. Combining a healthy exercise routine with a good diet emphasizing healthy fats, lean protein, and carbohydrates, mainly vegetables, and fruits, will help you successfully lose weight. This mixture helps the body burn calories stored as fuel and energy and stops the body from storing further fat from the food you are still consuming. But what happens to body fat when you lose weight—does it get expelled by sweat, urination, or breathing? Below is the revelation you may have been waiting for.

How Does Body Fat Leave Your Body?

Fat is a stored form of energy. Water and carbon dioxide are emitted as waste products when stored fats are broken down to produce energy during fat-burning. Water is discharged by respiration, sweat, and urination while CO2 is expelled through breathing. Consequently, the size of the fat cells decreases, making the body appear thinner.

How Does Fat Leave The Body?

It would be best if you created a calorie imbalance, often known as a calorie deficit, for fat to leave your body. This is a situation where your body burns more fats than you consume. In this condition, your body will start using the stored fat as energy, which will cause you to lose excess fat.

Since energy can never be destroyed, fat is a stored form of energy. So where does it go, then?[1]

Water and carbon dioxide are emitted as waste products when stored fats are broken down to produce energy during fat-burning. Consequently, fat cells shrink in size, making the body appear thinner.

Water is discharged by respiration, sweat, and urination while CO2 is expelled through breathing. Therefore, increased breathing and perspiration rates during an exercise program can improve the clearance of these waste products, assisting in accelerating the fat-burning process.

What Is Fat?

Adipocytes, a class of fat cells that make up fat tissue, also called adipose tissue, are present in numerous forms. Depending on where they are and what they do, these fat cells might be brown, white, or beige.

Brown Fat

Although adults also have a small amount of brown fat. It is mostly seen around the shoulders, spine, and neck in infants and babies. 

It is regarded as a good fat because it is essential for keeping you warm by burning fatty acids. Additionally, brown fat contains a robust capillary network that makes it simple to move oxygen and vital nutrients throughout the body.

Recently, researchers have focused on the possibility of using brown fat to manage or even treat obesity. It may burn white fat and calories when brown fat is recruited, just like a muscle. It’s interesting to note that thin persons frequently have more brown fat than obese people.

White Fat

The most prevalent form of adipocyte in the human body is white fat cells which serve as a significant energy source. In addition, these white fat cells provide fuel in the form of fatty acids whenever glycogen energy reserves are depleted.

The action of numerous crucial hormones, including leptin and insulin, which regulate appetite and blood glucose, respectively, is significantly regulated by white fat cells. Therefore, an excess of white fat can result in health issues like heart disease, diabetes, obesity, and weight gain.

Beige Fat

Although they work the same as brown fat and are formed from white fat, the cells of beige fat don’t store a lot of fat on the body; instead, they burn energy that generates heat.

According to research,[2] exercise may enhance the production of particular enzymes and hormones that can change white fat into beige fat. As they enhance energy expenditure and aid in removing unhealthy fat, beige, and brown fat are extremely beneficial to your health.

Healthy Vs. Unhealthy Fats

Healthy Vs. Unhealthy Fats
Healthy fats are good for your health. Photo: Shutterstock

While fats are a necessary component of a balanced weight-loss diet, some are better for your overall health than others. For example, the amount of bad cholesterol (LDL) can significantly increase when saturated fats in animal products, including fatty meats, whole-milk dairy products, butter, cheese, and trans fats in fried meals are consumed. 

However, unsaturated fats can significantly help raise HDL, also called good cholesterol levels, while lowering LDL levels (bad cholesterol). Canola oils, olive, salmon, avocados, and nuts are all sources of unsaturated fat. However, all fats contain a lot of calories, and eating excessive amounts of fat can result in major health problems like diabetes, high cholesterol, cancer, obesity, and heart disease.

Fats & Energy

Protein, carbs, and fats are the three crucial elements that give the body energy. But fats are the elements with the highest energy density, even though the body’s primary energy source is carbohydrates. 

According to the Centers for Disease Control and Prevention, lipids provide about twice the calories and energy per gram (9 kcal) as proteins and carbs, which have only 4 kcal/gram. The body uses this energy for essential biological functions carried out at rest by the basal metabolic rate and physical activity. These include digestion, hormone regulation, cell growth, and blood circulation. Any excess calories that are not used for energy right away are kept in the body as fat for later use.

How Does Fat Loss Work?

You may be thinking about “burning some fat” to feel better in your bathing suits at the pool or the beach. But what does that mean?

The main function of the normal fat cell is energy storage. So to take extra energy from foods that have too many calories; the body will increase the size and the number of fat cells. With a sedentary lifestyle, foods rich in calories will go as far as accumulating fat cells in our liver, muscles, or other organs to provide space for storing all this excess energy. 

Humans have historically done well with fat storage. The stored energy is made available for the muscle or other organs to use when there’s a deficit of energy or in high activities. In these circumstances, fat accumulation provided a survival advantage. People who tend to accumulate fat have more energy to survive harsh circumstances and could go longer without eating.

However, it is not common for humans to have a deficit of energy or carry out a high activity for a long time. As a result, numerous people have built up excessive fat reserves. The primary issue with extra fat today is that the adipocytes, which are the fat cells, don’t operate normally. They have unusually high energy storage rates and abnormally low energy release rates. In addition, these additional and expanded fat cells generate excessive amounts of several hormones. Such hormones impede fat metabolism, exacerbate illness, and raise inflammation. Adiposopathy is a pathological condition of excess fat and malfunction that makes treating obesity exceedingly challenging.

Two Ways The Body Burns Fat

Two Ways The Body Burns Fat
Calorie restriction and exercise are two ways the body burns fat. Photo: Shutterstock

The body “burns fat” in two ways when someone starts and sustains a new workout routine and calorie restriction. It first consumes the energy stored in the fat cells to power new activity. This is the first method the body loses fat. The second method is it reduces the amount of storage of fat.

Energy bundles or fatty acid molecules are released by fat cells into the bloodstream when the brain sends signals. The lungs, muscles, and heart take up these stored fatty acids, which disassemble them and use the energy in the bonds to carry out their functions. The leftovers are expelled through respiration, CO2 (carbon dioxide), or urine. The fat cells are left empty and rendered useless as a result. The body mops up the empty cast after a cell dies because the lifespan of the cells is normally short and is not replaced.

Subsequently, the body stops storing energy from food and transfers it directly to the required organs.

The body then adjusts by reducing the size and quantity of fat cells, which enhances digestion at rest, lowers inflammation, manages disease, and prolongs healthy lives. In the long run, if you keep this state, the body will reabsorb the excess empty fat cells and eliminate them as waste products, making you healthier and leaner overall.

Where Does Fat Go When You Lose Weight?

Fat cells dramatically reduce in size as the fat-loss process continues, resulting in visible changes to the body composition.

Byproducts of Fat Loss

Two significant byproducts are created when body fat is broken down for energy through intricate procedures within your cells: water and carbon dioxide. During respiration, carbon dioxide is released, and water is eliminated via sweat, urine, or exhaled air. Therefore, the elimination of these metabolites is significantly increased due to enhanced sweating and breathing during exercise.[3]

5 Tips To Lose Body Fat

Consume The Right Diet

Fad diets and fast fixes provide a simple substitute for switching your diet and maintaining a relatively healthy diet. However, these diets are frequently not sustainable, and you soon find yourself back where you started. So instead, adhere to these three straightforward suggestions to help prevent effects associated with following rapid weight loss fads.

  • Consume fiber: Fiber is not only important for a healthy digestive system, but it can also help you lose healthy body weight. Viscous fibers will bind to the water in the gut, resulting in more effective nutrient absorption and longer-lasting satiety. An additional 14g of fiber consumed per day can reduce hunger by 10% and promote weight loss. Consider including more foods with high fiber content like fruits, vegetables, and legumes in your diet to help you lose weight.
  • Cut out sugar: Carbs are the enemy of anyone attempting to lose weight; thus, it is advisable to avoid them whenever trying to burn fat. Since they can be broken down the quickest, the body uses carbs for energy and will store excess. Rice, oats, fruit, and vegetables should be your main sources of carbs because they are generally considered healthier options.
  • Do not cut out fats: Many people believe that to lose weight fast, you must stop consuming fat. While this is somewhat accurate, this is if you continue to consume saturated fats. However, maintaining mono- and polyunsaturated fat intake can aid in the weight loss journey. These healthy fats don’t just assist in lowering bad cholesterol and preventing cardiovascular disease but also help suppress appetite and prolonged satiety. In addition to curbing appetite, they also help in delivering a rich source of healthy nutrients, seeds, and fish.

Stay Hydrated

Drink lots of water since our bodies sometimes mistake thirst for hunger. Although food does contain some liquid that will keep you hydrated, you should try to get 80% of your water from liquids. To keep your body working properly, it’s crucial to ensure that any liquid lost during sweating is restored, especially when exercising. In addition, drinking enough water can help your body convert meals more effectively into energy and stifle your appetite.

Maintain Regular Workout

Visceral fat has the advantage of being easily influenced by aerobic exercise. The belly fat will begin melting if you try to incorporate regular cardio exercises, whatever suits you outside or in the gym. Physical activity should be a part of your fat loss journey because it effectively helps with burning fat and improves health. Exercises targeting the core and increasing muscle mass assist in keeping you toned and reduce the appearance of fat, especially those like dancing and running.

Control Your Eating

This is easier said than done. But keeping control of what you eat is one of the greatest and most sustainable ways to lose weight faster. Also, attentive eating will help you lose weight according to research[4] published in 2013. 

Here are some of the tips that will benefit you. 

  • Eat more frequently. If you want to lose weight, don’t adhere to the tradition of eating three meals a day. Instead, eat 5 to 6 light meals. This way, you’ll be able to spread your calorie intake. 
  • Take a large breakfast: You will need a large breakfast that will help prevent you from taking intermittent snacks. Also, the day’s activities will break down this large breakfast for energy. 
  • Keep a food diary: To successfully lose weight, you’ll want to burn more calories than you consume. And keeping records of what you eat daily is a great way to monitor your progress.

Get Proper Sleep

Make sure you get enough sleep because it has so many advantages. According to research,[5] sleeping less than 6 hours is a risk factor for obesity. To boost metabolism smoothly and keep your memory fresh and free of stress, aim for about 8 hours of sleep. This will help you avoid the temptation of taking snacks and choosing some fruit instead.


By now, you’ve known that fat leaves the body in the form of carbon dioxide and water. The carbon dioxide is excreted during respiration, while the water is excreted through the urine. To lose fat stores significantly, you’ll need to adhere to regular exercise and maintain a healthy diet. In addition, your overall diet should be planned to reduce sugar intake.

Frequently Asked Questions

What fat should I consume when on a weight loss regimen?

Reduce consumption of saturated fat. Instead, take mono- and polyunsaturated fats from tofu, olive oil, and cold water fish.

Should I plan my weight loss meal?

Yes. This is important because it enables you to track your progress.

What types of carbohydrates should I avoid to lose weight?

Avoid carbohydrates from processed foods.

Is sex enough exercise for me to lose weight?

While sex is a great exercise, it is insufficient to lose significant body weight. This is because, on average, sex lasts for only 10 minutes.

Does cardio exercise provide the best result?

Cardio has been considered to be among the best weight loss exercises. However, never get involved in cardio when hungry. The body needs the energy to fuel the exercise.

Can drinking water help me lose weight?

Yes. Sometimes, our body mistakes thirst for hunger. This leads to increased food consumption and hence weight gain. But if you drink more water, you’ll eat less.

Can proper sleep help me lose weight?

Yes. If you sleep appropriately, you’ll be able to perform better in daily activities and hence burn excess fat.

How often should I eat a day to lose weight?

It is recommended you eat 5-6 times a day. The best way to do this is to eat light meals between heavy meals; this will help you spread your calorie intake. 

+ 5 sources

MIDSS adheres to strict procurement guidelines and relies on peer-reviewed studies, academic research institutes, and medical associations. We work mainly with peer-reviewed studies to ensure the accuracy of the information. We avoid the use of tertiary references. You can read about how we ensure the accuracy and timeliness of our content in our editorial process.

  1. Meerman, R. and Brown, A.J. (2014). When somebody loses weight, where does the fat go? [online] ResearchGate. Available at:
  2. Aldiss, P., Betts, J.A., Sale, C., Pope, M., Budge, H. and Symonds, M. (2018). Exercise-induced ‘browning’ of adipose tissues. Metabolism-clinical and Experimental, [online] 81, pp.63–70. doi:
  3. Aliverti, A. (2016). The respiratory muscles during exercise. Breathe, [online] 12(2), pp.165–168. doi:
  4. Robinson, E., Aveyard, P., Daley, A., Jolly, K., Lewis, A.M., Lycett, D. and Higgs, S. (2013). Eating attentively: a systematic review and meta-analysis of the effect of food intake memory and awareness on eating. The American Journal of Clinical Nutrition, [online] 97(4), pp.728–742. doi:
  5. Theorell-Haglöw, J., Berglund, L., Berne, C. and Lindberg, E. (2014). Both habitual short sleepers and long sleepers are at greater risk of obesity: a population-based 10-year follow-up in women. Sleep Medicine, [online] 15(10), pp.1204–1211. doi:


Christine VanDoren, Nutritionist
Personal Trainer, Nutritionist, Health & Wellness Writer
Christine VanDoren created Edge of Longevity, an online personal training company, which helps people all over the world engage in a healthier lifestyle. After becoming an NSCA certified personal trainer and ACE nutritionist, she started spending her time training in the gym and online and creating content for Edge of Longevity, all of which is about how she has worked to better herself, and in turn, hopes to help others better themselves too. She believes the healthier one is, the happier one can be, and through Edge of Longevity, she hopes to spread that happiness to people in every country, every lifestyle, of every age and gender, and ethnicity. She warmly welcomes you to this community of people trying to make a change. In addition to sharing knowledge through her personal training and nutrition services, she enjoys writing articles and blog content over any health and wellness-related topic!


Drew is a retired ENT doctor who now lives in the Southeastern US. He was a member of the American Academy of Otolaryngology and a Fellow of the American College of Surgeons. He has a bachelor’s degree in Biology and Psychology and an MD degree. He completed his internship in General Surgery and Residency in Otolaryngology-Head and Neck Surgery and practiced for almost 30 years in all aspects of ENT, including a specialization in disorders of the ear and skull base. Drew is passionate about communicating his clinical experiences and making his knowledge more accessible to the general public by medical writing.

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