Most people, even doctors and dieticians and personal trainers, when asked, believed that the fat you lose if you stop eating, is converted to energy or heat.(1) If that were true, your body would be some kind of nuclear reactor turning matter into energy. But calories, the energy of the food you eat and use to live and think and move, doesn’t weigh anything.
Nobody really knows, in a fundamental way, what energy is. It seems like we should. Why are we paying those physicists? We do know, however, that it comes in different forms and can change between heat or light or movement or the other forms it can take. The calories you eat are in the form of chemical bonds between molecules. But those molecules are still there when you do the chemistry in your body that extracts the energy from those chemical bonds.
It turns out that the weight you lose when you burn fat and sugar mostly gets breathed out through your lungs in the form of carbon dioxide and water vapor. You can also get rid of the water though sweat and urine output. In fact most of the weight that gets exhaled doesn’t even come from the fat you burn. Most of that weight is oxygen that you also took in through your lungs. In chemical terms, one molecule of triglyceride—the the main ingredient of body fat—combines with 78 molecules of oxygen to produce 55 molecules of carbon dioxide, 52 molecules of water, and some energy. The chemical bonds in the fat have more energy, like a coiled spring, than the chemical bonds in CO2 and H2O, those bonds are like a more un-coiled spring.
Somebody (1) did the math and 22 pounds of fat requires 64 pounds of inhaled oxygen which turns into 62 pounds of carbon dioxide and 24 pounds of water. So 86 pounds of stuff was transacted but only 22 pounds of fat were involved after all.
It’s kind of like burning a log. It mostly goes up in smoke. Or it’s like your car. The gasoline in the tank, plus air intake, goes out the tail pipe.
I leave you with the homework question, why can’t you lose more weight by just breathing harder.
And you thought science was boring.
1. R. Meerman, A. J. Brown. When somebody loses weight, where does the fat go? BMJ, 2014; 349 (dec16 13): g7257 DOI: 10.1136/bmj.g7257
John DiTraglia, M.D., is a pediatrician in Portsmouth. He can be reached by email at firstname.lastname@example.org or call 740-354-6605.