A common misconception is that, when we lose weight, our fat is converted to muscle. Or energy. Or poop. The reality, though, is that we breathe it out as carbon dioxide. It literally disappears into thin air.
Their findings were published earlier in the week in the BMJ. They surveyed over 150 doctors, dietitians, and personal trainers, and more than 50% of them thought the fat was converted to energy or heat. Meerman said he was stunned at the ignorance on this pretty basic biochemical process.
The researchers use the calculation below to show that fat (plus oxygen) is metabolized mainly into carbon dioxide, and also water that goes into urine or gets used up in other metabolic processes.