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Hey, Your Breath Smells Like Fat

Two Australian biochemists demonstrate that the errant holiday pudge you’re burning at the gym is expelled largely through exhalation.

Hey, Your Breath Smells Like Fat

Illustration by Tyler Hoehne

It’s almost the new year. Time for resolutions and a game plan for chiseling away at that extra layer the holiday season so unceremoniously padded your midsection with. It’s not going to be fun, but you’ve wrought this evil upon yourself. So while you’re waiting on hold to renew that gym membership, ponder this: Do you really know where the fat you’re burning goes?


As crazy as it may sound, you’re breathing most of it out.

Chances are you thought it gets converted into energy, or turns into muscle, or maybe just gets excreted and is left to the sewer overlords beneath the porcelain throne—all fair guesses, to be sure, but common misconceptions.

Ruben Meerman and Andrew J. Brown of the University of New South Wales, the biochemists behind the study that appeared in the latest British Medical Journal, told the BBC, “None of this biochemistry is new, but for unknown reasons it seems nobody has thought of performing these calculations before,” referring to their biochemical mapping of fat exiting the body.

Let’s break this down: Fat from the food you consume is stored as triglyceride (comprised of carbon, hydrogen, and oxygen) in the body. When you burn fat, and break it down, approximately a fifth of the triglyceride becomes water (H20), which your body can excrete in a variety of ways, and the remainder becomes carbon dioxide (CO2), which can simply be exhaled.

“Our calculations show that the lungs are the primary excretory organ for fat,” the duo reports, going on to reiterate the oft-heard advice of “eat less, move more” to those seeking to lose weight and concluding their study with the recommendation that their findings “be included in secondary school science curriculums and university biochemistry courses to correct widespread misconceptions about weight loss.” (Hey, even dietitians, personal trainers, and family doctors are still getting this wrong.)

Now that’s some food for thought.

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