You learn early in chemistry class that matter cannot be created or destroyed; it can only change form. So, how do those rules apply to the human body? Specifically, where does fat go when it "disappears"? Does it turn into something else? Is this all as mysterious as it seems?
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The answer is: kind of. Shape reports that, according to a recent study from the British Medical Journal that surveyed doctors and biochemistry students, even those science folk weren't quite sure what happens to fat after you burn it off. Researchers also learned that an alarming number of personal trainers and nutritionists believe fat converts to energy or heat — which isn't actually true.
Researcher Ruben Meerman traced atom pathways and determined that 80% of the atoms from fat molecules leave the body through your lungs. This means you're actually releasing most fat through carbon dioxide via your breath. The remaining 20% is released through water in the form of sweat, urine, tears, and other bodily fluids. Turns out there's actual meaning behind the phrase "sweat it out."