Basics How Does Fat Leave the Body? By Darla Leal | Reviewed by a board-certified physician Updated November 19, 2018 Pin Flip Email Print Show Article Table of Contents Myths Energy and Fat Metabolism What Is Fat? During Fat Burning Where Fat Goes Ways to Improve Fat Loss View All Back To Top stockvisual / Getty Images More in Weight Loss Basics Procedures Nutrition for Weight Loss Exercise for Weight Loss Diet Plans Medications Pills and Supplements We live in a society obsessed with fad diets and weight loss. You may even be trying to shed some body fat. Have you ever wondered where fat goes when you lose it? Myths There are misconceptions about fat loss among doctors, dietitians, and fitness professionals according to physicist Ruben Meerman. His fat metabolism research was published in the British Medical Journal and suggests that most health professionals don’t know how weight loss works at the molecular level. The following are common myths about fat metabolism, according to Meerman: Fat turns into muscleFat converts into energyFat escapes through your colon Energy and Fat Metabolism Most of us believe that fat turns into energy and is burned off during exercise or when calories are reduced. Meerman suggests that this belief violates the law of conservation of mass. He believes that the “energy in/energy out” theory stems from university science courses focusing only on energy production. What has been overlooked, according to Meerman, is the respiratory component necessary to completely metabolize human fat. There may be misconceptions regarding the byproducts (CO2 and H20) of energy production and how they leave the body, according to Tony Maloney, an ACSM-certified exercise physiologist. Meerman is clarifying that the majority is exhaled through the lungs and explains how fat actually leaves the body, says Maloney. The research sheds new light on common myths about fat metabolism. It makes sense that fat doesn’t magically turn into muscle or exit your body when you poop. Also, what you have believed about energy and fat loss is not entirely wrong considering fat is your secondary energy source. The point of the research is not to argue that fat is used or converted into energy, but more how it actually leaves the body, suggests Maloney. There is more to the fat loss equation than just “energy in/energy out.” Understanding fat metabolism at the cellular level will clarify how and where fat goes once it is burned. What Is Fat? The clinical term for body fat is adipose tissue. There are two different types in the human body. The white adipose tissue is primarily responsible for energy storage and releasing fatty acids when fuel is low. Your body contains mostly this type of fat. It is stored beneath the skin and surrounding organs. This is the kind of fat that most of us are trying to lose. Brown adipose tissue is considered good fat that helps regulate body temperature. It’s derived from muscle tissue and burns calories to keep you warm. Brown fat also contains more capillaries than white fat and shuttles valuable nutrients and oxygen throughout the body. Fat is made up of individual cells called adipocytes (cells that contain fat). The human body contains billions of fat cells ranging in different sizes. White fat cells are filled with one large fat droplet surrounded by water, salts, and protein. The fat droplet is comprised mostly of triglycerides (glycerol and three fatty acids). High levels of triglycerides in the bloodstream have been shown to increase your risk of heart disease and stroke. Brown fat cells contain multiple fat droplets and considerably more water, salt, and protein. These cells are also filled with lots of mitochondria responsible for the chemical energy that burns calories to produce heat in your body. The white adipose tissue is the fat measured during a body fat assessment. If you’re healthy and not overweight, white fat makes up approximately 20 percent of total body weight in men, and 25 percent in women. What Does Fat Do? Fat is made up of cells in your body that are used primarily for stored energy and protection, according to Maloney. The body uses this stored energy for working muscles as well as a host of other metabolic pathways and enzymatic breakdowns. When you consume more calories than your body needs, it will store the rest within your fat cells or adipocytes. The storage form of energy is known as triglycerides, a type of fat or lipid collected within individual fat cells. Besides providing energy, stored fat also helps insulate the body and protect vital organs. During Fat Burning Before explaining what happens during the fat burning process, it will help to understand where all the weight within the fat cell comes from. Meerman indicates the average American breathes in about 1.5 pounds of oxygen daily. This is in addition to what you eat and drink every day. According to the latest government figures, the average person consumes approximately five to 7.8 pounds of food and beverages daily. What you eat and what you breathe needs to exit your body somehow if you want to lose weight. During the fat burning process, the body converts fat into usable energy causing the fat cell to shrink, according to Maloney. This metabolic energy conversion also generates heat which helps to control body temperature. At the same time, oxygen is also converted into byproducts. Many enzymes and biochemical steps are involved to completely break down a single triglyceride molecule, according to Meerman. Some of the fat is available for usable energy, but carbon dioxide (CO2) and water are also released from the fat cell during the process. In fact, a large percentage of carbon dioxide (CO2) is created and expelled from the body when you burn fat. Where Fat Goes Most of us really don’t think about where fat goes when we lose it. We’re just happy the scale says it’s gone. You may be curious to know fat doesn’t magically disappear after going through the fat burning process. Research calculations show when fat is lost, 84 percent is exhaled as carbon dioxide. The remaining 16 percent is excreted as water. During the conversion of energy, carbon dioxide and water are byproducts or waste, according to Maloney. They are excreted via urine, perspiration, and exhalation. Meerman provides an excellent graphic on everything you eat and where it all goes in his research. It is summarized below: 148 ounces in 148 ounces out 23oz. oxygen metabolized into 27oz. carbon dioxide 15oz. food 1oz. urine solids 10oz. metabolic water 110oz. water unchanged 110oz. water food moisture urine beverages exhaled vapor plain water sweat feces What You Eat and Where it Goes The research also reveals the lungs as the primary organ used to remove fat from your body. Ways to Improve Fat Loss Since fat leaves the body by exhaling carbon dioxide, you may be wondering if breathing faster will help you lose weight. Unfortunately, this isn't an effective method. You will only cause hyperventilation, feel dizzy, and possibly faint. There are healthy ways to increase oxygen intake and improve weight loss. Working toward improving your metabolic rate would be a great start. This includes being more active in general and participating in regular exercise. Exercise increases your metabolism or the rate your body uses energy. The American College of Sports Medicine (ACSM) recommends at least 150 minutes of moderate-intensity exercise per week. Meerman suggests you can increase carbon dioxide (CO2) exhalation by performing physical activities that double the metabolic rate. For example, swapping out one hour of rest with exercise like jogging removes more CO2 from the body and improves your ability to lose fat. Other basic suggestions to increase your metabolic rate and rid your body of CO2 include the following: Take the stairs instead of the elevator/escalator.Park your car far away and walk more.Engage in active play time with your kids.Stand at your computer vs. sitting.Take walk and stretch breaks at work.Stay active over the weekend and avoid being a couch potato. Your body is also at work removing CO2 while you sleep. In fact, you exhale approximately seven ounces of carbon dioxide which is 25 percent of the daily amount you need to get rid of. This means you are waking up starting your day ahead of the game. A Word From Verywell The lungs are the primary excretory organ for fat, according to Meerman. He suggests the key to weight loss is unlocking the carbon stored in fat cells. What is recommended for successful fat loss is to eat less and move more. This means reducing caloric intake to cause an energy deficit, but also exercising regularly. Exercise will naturally increase the rate oxygen is used and help remove more carbon dioxide from your body. Was this page helpful? Thanks for your feedback! Get nutrition tips and advice to make healthy eating easier. Email Address Sign Up There was an error. Please try again. Thank you, , for signing up. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Labros Sidossis et al., Brown and beige fat in humans: thermogenic adipocytes that control energy and glucose homeostasis, Journal of Clinical Investigation, 2015 Ruben Meerman et al., When somebody loses weight, where does the fat go?, The British Journal of Medicine, 2014 Peter Janiszewski, Ph.D., When you lose weight, where does the fat ACTUALLY go?, Obesity research, PLOS Blog, 2015 Stephanie Dutchen, What Do Fats Do in the Body?, Inside Life Science, National Institutes of Health, 2010 Continue Reading Article The Differences Between Fat and Fat-Free Body Mass Article Do You Know Your Body Fat Percent? Article Does You Know Why Your Body Is Changing Shape as You Get Older? Article What Are the Different Types of Fat? Article How You Can Reduce Non-Essential or Excess Body Fat Article How Can I Burn More Fat When Exercising? Article What Is a Calorie in Food and Exercise? 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