Where does body fat go when we lose weight? The answer is stranger than you expect

When a person loses weight, their body burns through stored fat reserves to generate the energy it needs. Fat stored in the body comes from the food we eat, which is broken down in the digestive system into fatty acids. These fatty acids are essential for various bodily functions and are stored in fat cells to be used as an energy source later on. The body primarily stores fat in two forms: subcutaneous fat, found just under the skin, and visceral fat, which accumulates around the organs.

In times of calorie deficit, such as when people diet or exercise, hormonal and neural signals prompt fat cells to break down stored fat through a process called lipolysis. Fatty acids released from these broken-down fat cells travel to the mitochondria, often referred to as the body's power stations, where they undergo a process known as beta-oxidation.

During beta-oxidation, fatty acids are broken down into compounds that cells use to produce energy. The by-products of these reactions are carbon dioxide and water, both of which leave the body.

Contrary to common belief, most of the fat lost by the body does not exit through sweat. Instead, around 84% of the lost fat is exhaled as carbon dioxide when we breathe. The remaining 16% of fat is converted into water, which is eliminated through sweat and other bodily fluids. These percentages, while estimates, are consistent with the researchers' calculations.

It's important to note that losing weight does not mean breathing faster causes fat loss. Breathing is simply the route through which the by-products of fat burning, namely carbon dioxide and water, leave the body. The fat burning itself is triggered by the body's energy needs not being met by dietary intake, leading it to tap into its stored fat reserves. Ultimately, maintaining a calorie deficit through a combination of diet and physical activity remains the key factor in prompting the body to utilize its fat stores.