When a person loses weight, have you ever wondered where it goes? Scientists at the University of New South Wales in Australia have put together a calculation to explain the process. And it turns out most expert theories are wrong.

The report, published in the British Medical Journal (2014; 349, g7257), featured a survey of 50 family doctors,
dietitians and personal trainers who were asked what they thought happens to fat once it’s been “burned.” The majority of respondents believed that fat converts to energy or heat. Others suggested that fat becomes muscle or is eliminated from the body via feces. According to the scientists’ calculation, it turns out that fat mostly converts to carbon dioxide and exits the body through breath. The remaining portion becomes water and leaves the body through urine, sweat, tears and other bodily fluids.

“Our calculations show that the lungs are the primary excretory organ for fat,” the authors stated. “Losing weight requires unlocking the carbon stored in fat cells, thus reinforcing that often heard refrain of ‘eat less, move more.’”

To view the full report—which includes a video cartoon that explains the process—visit www.bmj.com/content/349/bmj.g7257.

Ryan Halvorson

Ryan Halvorson is an award-winning writer and editor. He is a long-time author and presenter for IDEA Health & Fitness Association, fitness industry consultant and former director of group training for Bird Rock Fit. He is also a Master Trainer for TriggerPoint.

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