Where Does Fat Go When We Lose Weight?

Where Does Fat Go When We Lose Weight?

Losing weight has become a worldwide obsession. All sorts of fitness methods, diets and health tips seem to offer the quickest way to success. But where does that so-called 'burned' fat go? Most theories don't have an answer to that. However, a new Australian study claims that it does.


The biggest misconception among scientists, doctors and dieticians is that when we lose fat, that mass is converted to warmth and energy. "It is remarkable how little we know when it comes to the metabolistic process of burning fat", says Andrew Brown, head of the UNSW of Biotechnology and Biomolecular Sciences.



According to the study, the fat-mass we lose is not converted to warmth, nor to energy, but to carbon dioxide. Carbon dioxide is an inorganic compound which is colourless and odourless and which can be found in the atmosphere. "When we burn fat, we breath it out in the form of thin air", says Ruben Meerman, Australian physicist and chief-researcher of the project.


Meerman's interest in the subject was sparked by personal experience. "In 2013 I lost 15 kilograms, and I was curious to know where those kilograms went. In a time like today, where obesity and anorexia are common, I felt it was important that we get to know and understand the biological mechanisms behind weight loss."



What exactly happens when you lose weight, is best explained using a concrete case, according to Meerman. "When you follow the atoms concerned during a weight-loss of 10 kilograms, you can see that 8,4 kilograms of the fat-mass are converted to carbon dioxide, which leaves the body through the lungs. The remaining 1,6 kilograms are converted to water, which can be excreted by urine, sweat, tears, breath and other bodily fluids."


The reason why this has remained a secret thus far, is probably because the carbon dioxide is invisible, so we do not notice that we 'lose' it.



A large scale survey, performed by Meerman and his colleagues to 150 doctors and dieticians, showed that more than 50% of the participants thought that fat is turned energy when it's burned. Other respondents thought that fat turns into muscle mass during exercise. According to the researchers, these misconceptions show a remarkable ignorance when it comes to the basic biological functioning of the human body.


A question which scientists were often asked during the research, was whether you could burn fat by simply breathing more. The answer is of course no. There were also a couple of test persons who wanted to know whether breathing a lot negatively affects global warming. The answer, again, is no. "The carbon dioxide molecules which are exhaled by human beings, has been stuck for some months or years in the earth, in food or in human body-fat, and simply returns to their natural environment: the atmosphere", says Meerman.

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