You’ve probably never given much thought to where your excess pounds go when you burn them off. It doesn’t matter where they go as long as they go, right? If asked, you’d probably say your body converts those fat cells to muscle or excretes them as sweat or feces. But in fact, a tag team of Australian scientists have discovered that lost weight mostly leaves the body through the lungs, in the form of carbon dioxide. A small remnant of metabolized fat leaves the body as water excreted in tears, urine, sweat, and feces.
The Mystery of the Disappearing Fat
Australian physicist and TV presenter Ruben Meerman became intrigued by the process of fat metabolization when he lost 15 kg, or about 33 pounds, in 2013. Meerman simply wanted to find out where the missing fat went. In pursuit of that goal, he taught himself some of the basics of biochemistry, and sought the expertise of Andrew Brown, a professor and head of the School of Biotechnology and Biomolecular Sciences at the University of New South Wales. Together, the two scientists calculated that metabolized fat cells mostly become carbon dioxide and water.
Fat cells, or triglycerides, form when the body stores excess calories for later use. When you lose weight, you’re metabolizing these stored fat cells and using them for energy in a way that doesn’t reduce the rest of your mass. Triglyceride cells consist of three basic molecules: oxygen, hydrogen, and carbon. When you metabolize these cells through diet and exercise, you break the cells down into their three component atoms through the process of oxidization.
In a paper published in the British Medical Journal, Brown and Meerman demonstrated that losing 10 kg of fat produces 28 kg of carbon dioxide, expelled through the lungs, and 11 kg of water expelled through various other bodily functions. In order to facilitate this metabolic process, you must inhale 29 kg of oxygen.
Meerman and Brown were able to account for each individual atom of the 10 kg of metabolized fat in their calculations. They demonstrated that the lungs secrete 8.4 kg of those atoms as carbon dioxide. The 1.6 kg left behind turns into water. The entire metabolic process requires nearly three times the weight in oxygen of the total fat being lost. The excess water and carbon dioxide come from the metabolization of the oxygen.
Improving Our Understanding of Weight Loss
The scientists believe that these findings can fundamentally change our understanding of weight loss. When Meerman and Brown surveyed 150 dieticians, physicians, and personal trainers about what they thought happened during the process of fat metabolization, more than half said they thought the disappearing fat converted to heat or energy. Others said the fat cells turned into muscle cells or were excreted, presumably whole, in feces.
Meerman told Science Daily, “This violates the Law of Conservation of Mass. We suspect this misconception is caused by the energy in/energy out mantra surrounding weight loss.” Meerman and Brown believe that this new information about fat metabolization should be incorporated into university and secondary school curricula.
While Meerman and Brown’s calculations do indicate that much of the fat we burn is exhaled as carbon dioxide, that doesn’t mean that breathing harder in and of itself can speed weight loss. Breathing in more oxygen than your body needs will just cause you to hyperventilate and maybe even pass out. However, raising your metabolic rate through exercise can increase your base carbon loss by as much as 20 percent.
The average person exhales about 200 ml of carbon dioxide per minute for an average carbon loss of 200 grams per day, around a third of which occurs during sleep. An hour of vigorous exercise, like jogging, can increase your daily carbon loss to as much as 240 g.
These findings paint a clearer picture of how weight loss occurs, but they don’t change what we already know about how to lose weight. Losing weight still requires burning more calories than you ingest — although new, effective prescription weight loss drugs like the one being developed at Harvard University may soon be available from Canada Drug Pharmacy.
What About the Carbon Footprint of Weight Loss?
Many people these days are concerned about lessening their carbon footprints, but Meerman and Brown assure dieters that losing weight does not contribute to global warming. Meerman, who educates Australian high school students about the science of climate change, points out that the carbon atoms released during weight loss go back into the atmosphere relatively soon after being consumed. That means they don’t cause atmospheric changes on the same scale as carbon atoms released from fossil fuels, which have been trapped in those fuels for millions of years.
If you’ve ever wondered what happens to the extra pounds you shed on a diet, science now has the answer. Those metabolized fat cells are excreted in the form of carbon dioxide and water. So the next time you hit the gym, you can rest assured that your extra pounds are literally melting off.