With the rise of the wellness movement, countless people are focused on burning calories and getting lean.
But have you ever thought about exactly how fat disappears from your body?
As part of a study on the topic, scientists from the University of New South Wales posed a simple question to health professionals: When somebody loses weight, where does the fat go?
Of the 150 doctors, dietitians, and personal trainers they surveyed, they said only three respondents answered the question correctly.
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Writing for The Conversation, assistant scientist Ruben Meerman and Andrew Brown, professor and head of biotechnology and biomolecular sciences at UNSW, explained the results of the research — and, like the health professionals questioned, you might be surprised at what the scientists found.
"The most common misconception by far was that fat is converted to energy," the scientists wrote. "The problem with this theory is that it violates the law of conservation of matter, which all chemical reactions obey."
Other respondents believed fat was converted into muscle, which, they explained, "is impossible."
Another theory was that it leaves the body through the colon, which is also incorrect, according to the duo.
So what's the answer?
"[F]at is converted to carbon dioxide and water," they wrote. "You exhale the carbon dioxide and the water mixes into your circulation until it’s lost as urine or sweat.
"If you lose 10kg of fat, precisely 8.4kg comes out through your lungs and the remaining 1.6kg turns into water. In other words, nearly all the weight we lose is exhaled."
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They added that while this may surprise people, "almost everything we eat comes back out via the lungs.
"Every carbohydrate you digest and nearly all the fats are converted to carbon dioxide and water."
The same goes for alcohol and protein, apart from a small amount from the latter that is turned into urea and other solids, and excreted as urine.
The scientists pointed out that the only food that arrives at your colon undigested is "dietary fiber," such as sweetcorn. The rest is absorbed into the bloodstream and organs.
"After that, it’s not going anywhere until you’ve vaporised it," they wrote.