Where does weight loss go? © Getty Images

When we lose weight, where does the fat go?

When you burn off those extra pounds, the fat is transformed into other by-products through a series of difference process.

Asked by: Melissa & Evis, Cyprus


Ultimately most fat ends up as carbon dioxide and water, but only after many transformations. The fat in white adipose tissue consists of fatty acids, stored very efficiently as triglycerides, which can be released to provide energy when needed. You lose weight when the food you eat doesn’t provide all the energy your body needs and so some of these fatty acids are released into the bloodstream, transported by a special blood protein and taken up by cells that need energy. If there is sufficient oxygen available, a series of enzymes then converts the fatty acids into carbon dioxide, water and adenosine triphosphate (ATP) – the immediate source of energy for powering muscle, liver and other cells. Since most of the components of ATP are reused inside the cell to make new ATP, the end product of all this activity is that the atoms that once made up your fat leave your body as breath, sweat and urine.


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.