LAHORE: When people lose weight, they often assume that excess body fat is mainly converted into energy and released through sweat. However, the science behind fat loss reveals a more surprising answer: much of the fat leaves the body through the lungs.
The body stores fat mainly in two forms: subcutaneous fat, which lies beneath the skin, and visceral fat, which is stored deeper inside the body around internal organs.
When the body enters a calorie deficit, hormonal and metabolic signals encourage fat cells to break down their stored triglycerides. This process, known as lipolysis, releases fatty acids that can be used by cells as an energy source.
The fatty acids are transported into mitochondria, the structures often described as the cells’ energy-producing centres, where they undergo a process called beta-oxidation.
During this process, fatty acids are broken down into compounds that help generate energy. The overall metabolism of stored fat ultimately produces carbon dioxide and water.
This is where the surprising part comes in. Most of the carbon from the fat that is metabolised leaves the body as carbon dioxide through exhalation.
According to widely cited calculations, about 84% of the mass of metabolised fat is converted into carbon dioxide, which is released when we breathe out, while roughly 16% becomes water and leaves the body through urine, sweat and other bodily fluids.
This does not mean that simply breathing faster causes significant fat loss. The body must first mobilise and metabolise stored fat, which generally occurs when energy expenditure exceeds energy intake over time.
In simple terms, when stored fat is metabolised, its atoms are largely converted into carbon dioxide and water. So, contrary to the common belief that fat is primarily “sweated out,” a substantial proportion ultimately leaves the body through exhaled breath.