Q&A: Where Does Fat Go When You Lose Weight?
When you lose weight, the pounds disappear… but where does fat go when you lose it? Do you know the correct answer? Continue reading, because the answer might not be what you think.
A gap in health literacy
Obesity rates are soaring and a worldwide obsession over fad diets and weight loss is holding strong. Yet, there is confusion and ignorance about the metabolic process of fat loss. Few know how fat actually vanishes from the body… and this gap in knowledge is pretty extensive.
Many health professionals such as physicians, dietitians and personal trainers cannot correctly answer the question of where body fat goes when people lose weight, a 2014 University of New South Wales School study shows.
Common misconceptions about fat
In the fat study, Ruben Meerman, a physicist and Australian TV science presenter, and Professor Andrew Brown, head of the University of New South Wales School of Biotechnology and Biomolecular Sciences, conducted a survey among 150 health professionals, asking the question, “When somebody loses weight, where does it go?”
The top three answers to the question, “When somebody loses weight, where does it go?” were:
- Fat is converted to energy or heat
- Fat is converted to muscle
- Fat is excreted in the feces
All three responses are wrong.
A closer look at the incorrect answers
“The misconceptions we have encountered reveal surprising unfamiliarity about basic aspects of how the human body works,” the authors say.
Let’s take a closer look at the three misunderstandings listed earlier.
1. Fat is converted to energy or heat: More than 50 percent of the 150 health professionals surveyed thought the fat was converted to energy or heat. This theory is incorrect because it violates the Law of Conservation of Mass, which all chemical reactions obey. (The Law of Conservation of Mass states that the mass of an object never changes, no matter how the particles rearrange themselves. The mass can never be created nor destroyed.)
2. Fat is converted to muscle: Other respondents thought the metabolites of fat were converted to muscle. This is scientifically impossible. Fat cannot magically turn into muscle.
If not energy, muscles or the toilet, where does fat go?
The correct answer to the question, “When somebody loses weight, where does it go?” is that most of the fat mass is breathed out as carbon dioxide. It goes into the air around you. Yup, the lungs are the primary excretory organs for fat!
You read that right, most of the byproducts of fat leaves the body through the respiratory system. This surprises just about everyone, but actually, almost everything we eat comes back out through the lungs.
Every carbohydrate you digest and nearly all fats are converted to carbon dioxide and water. This holds true for alcohol. Protein shares the same outcome, except a small part of it that turns into urea and other solids, which is excreted as urine.
Triglycerides (fat molecules)
To understand this concept of how fat is released from the body, it is helpful to first look at what a fat molecule is. Excess dietary carbohydrates and protein are converted to a type of fat called triglyceride. Triglycerides are the predominant type of fat (lipid) within the body.
When people strive to lose weight, they are attempting to metabolize these triglycerides while keeping their fat-free mass intact.
Triglycerides are comprised of three types of atoms: carbon, hydrogen and oxygen. Triglyceride molecules can be broken down only by unlocking these atoms, through a process known as oxidation. The complete oxidization of a single triglyceride molecule involves many enzymes and biochemical steps, but the whole process can be summarized by one chemical formula.
The calculation that shows how we “lose weight”
In their study, the adipose sleuths, Meerman and Brown, started with this chemical formula, which describes what happens when you burn one molecule of triglyceride:
C55H104O6+78O2 —> 55CO2+52H2O+energy.*
This formula illustrates that when you metabolize fat, you end up with carbon dioxide, water and energy (ATP).
By firing up their calculators, and tracing every atom’s pathway out of the body, Meerman and Brown were then able to show that losing (oxidizing) 10 kilograms (22.0 pounds) of fat requires inhaling 29 kilograms (63.8 pounds) of oxygen and that this metabolic process produces 28 kilograms (61.6 pounds) of carbon dioxide and 11 kilograms (24.25 pounds) of water.
The proportion of mass that ends up as CO2 (carbon dioxide) versus H2O (water) ends up being 84 percent CO2 compared to 16 percent H2O.
If you follow the atoms in 10 kilograms of fat (22.0 pounds) as they are ‘lost,’ 8.4 of those kilograms (18.48 pounds) are exhaled as carbon dioxide through the lungs, proving that the lungs are the primary excretory organ for weight/fat loss.
The remaining 1.6 kilograms (3.52 pounds) becomes water, which may be excreted in urine, feces, sweat, breath, tears and other bodily fluids. (See above diagram.)
In other words, nearly all the weight we lose is exhaled. To explain why this is obvious to so few people, the authors state it is because the carbon dioxide gas we exhale is invisible.
Pounds in versus pounds out
Meerman and Brown say that the reason we gain or lose weight is much less puzzling if we keep track of all the pounds, not just calories.
According to government statistics, Americans consume an average of 3.55 kg (125 ounces) of food and beverages every day. Of that, 430 grams (about 15 ounces) is solid macronutrients, 17 grams (0.6 ounces) is fiber and the remaining 3.11 kg (110 ounces) is water.
These figures do not illustrate that Americans inhale more than 660 grams (23 ounces) worth of oxygen per day. According to the fat researchers, this figure is equally important for your waistline.
“If you put 3.55 kg (125 ounces) of food and water into your body, plus 660 grams of oxygen (23 ounces), then 4.2 kg (148 ounces) of stuff needs to come back out, or you’ll gain weight. If you’re hoping to shed some weight, more than 4.1 kg (144.6 ounces) will have to go.
The 430 grams (15.2 ounces) of carbohydrates, fats, protein and alcohol most Americans eat every day will produce exactly 770 grams (27.1 ounces) of carbon dioxide plus 290 grams (10.2 ounces) of water (about one cup) and about 31 grams (1.1 ounces) of urea and other solids excreted as urine. (See above chart.)
An average 75kg (165 pound) person’s resting metabolic rate (the rate at which the body uses energy when the person isn’t moving) produces about 590 grams (21 ounces) of carbon dioxide per day. No pill or potion you can buy will increase that figure, despite the bold claims you might have heard.
The good news is that you exhale 200 grams (7 ounces) of carbon dioxide while you’re fast asleep every night, so you’ve already breathed out a quarter of your daily target before you even step out of bed.”
Can breathing more increase weight loss?
One of the most frequently asked questions the authors have encountered is whether simply breathing more can cause weight loss. The answer is no.
Breathing more than required by a person’s metabolic rate leads to hyperventilation, which can result in dizziness, palpitations and loss of consciousness. The only way you can consciously increase the amount of carbon dioxide your body is producing is by moving your muscles.
With that being said, the oxidization and metabolization of triglycerides is most effective when your breathing is efficient.
Eat less, exhale more
“Metabolizing 100 ounces of fat consumes 290 ounces of oxygen and produces 280 ounces of carbon dioxide plus 110 ounces of water. The food you eat can’t change these figures.
Therefore, to lose 100 ounces of fat, you have to exhale 280 ounces of carbon dioxide on top of what you’ll produce by vaporising all your food, no matter what you eat. Keeping the weight off simply requires that you put less back in by eating than you’ve exhaled by breathing.”
Unhealthy eating can easily disrupt this balance. A single 100 g muffin, for example, provides around 20% of an average person’s total daily energy requirement. “Physical activity as a weight loss strategy is, therefore, easily foiled by relatively small quantities of excess food,” write the authors.
The solution is a traditional one – eat less unhealthy foods, more high quality whole foods and move more.
Meerman and Brown’s 2014 fat study demonstrates that when it comes to understanding where fat goes when humans lose weight, there is a tremendous gap in health literacy, especially among health and fitness professionals. Their study proves that most people need better education on this subject.
It is time to debunk the misconceptions about how fat is lost and teach people that when somebody loses weight, the lungs are the primary excretory organ for fat. Most of the fat mass metabolized is exhaled as carbon dioxide and vaporized into the air around us.
Meerman and Professor Brown concluded their study by recommending that, in order to correct the widespread misconceptions about weight loss that exist among the general public and health professionals, it is recommended that these basic concepts about weight and fat loss be included in secondary school curriculums and university biochemistry courses.
When looking to achieve fat loss, it is important to look at the whole picture, one that includes unlocking the carbon stored in fat cells and enforces the “eat less crap, move more” concept.
Hopefully, with increased exposure to literature like this, more and more people will become enlightened about how fat leaves the body when you lose weight. It’s definitely something to think about next time you hit the gym, go for a walk, or enjoy a run. Losing fat can be exhausting, but it’s as natural as breathing. 🙂
If you have enjoyed this article, Q&A: Where Does Fat Go When You Lose Weight?, please help spread the knowledge by emailing this post to a friend or sharing it via social media. Thank you!
I want to hear from YOU! What do you think about this article? What are your thoughts about Ruben Meerman and Andrew Brown’s study? Let’s get a discussion going… please comment below this post.
- Before reading this article, did you know that the lungs are the primary excretory organs for weight loss and that most of fat’s byproducts are exhaled as carbon dioxide and vaporized into the air around us?
- Were you surprised by anything shared in this article?
- What is your most successful method for fat loss?
When she is not helping others to slay fat, build muscle, and live amazing lives, Jennifer can be found exploring the outdoors with her dogs, cooking, traveling and playing/coaching lacrosse. She also enjoys reading and writing about food culture, history and the science of human movement.