Where does fat go?

“Matter cannot be created or destroyed only changed” this phrase definitely applies here. This question of “where does fat go?” has been known for centuries yet many people are still unaware of the correct answer, so where does our body fat actually go when we lose weight? Many people seem to think we “burn” the fat off or that it is released as “sweat” or in our urine or excrement. Respiration is the process of breaking down glucose or respiratory substrates (e.g. lipids or proteins) into inorganic, smaller, substances such as carbon dioxide and water, this process produces ATP which is used to release energy during hydrolysis. If we apply this question to the simple respiration equation we can see that carbon dioxide is a main product of this biological process. Fat stores are not released as excrement; food is released, some food is not stored on your body as ‘visible fat’ as most of the “food” is metabolized or released as excrement. The ‘visible fat’ is within you, it does not pass through the intestines and is not released as excrement. The fat that is ‘visible’ is the fat that is not metabolized during the day and so is stored on our body, most of this fat when we lose weight is metabolized into carbon dioxide and some is also released in bodily fluids.

Around 84% of our fat stored in adipose cells is released in the form of carbon dioxide and around 16% is released as water. A human fat molecule contains 6 molecules of oxygen, these are exchanged between water and carbon dioxide molecules; around 4 of these oxygen atoms are released when combined with carbon as carbon dioxide. This means 10kg of fat would be released as 8.4kg of carbon dioxide. Many people are puzzled about this question as carbon dioxide is not visible and only turns solid at -78 degrees it can be hard to believe that the fat we stored is mainly released as colourless gas. Concisely, we breathe out our fat when we lose weight.

For further reference: ‘The mathematics of weight loss: Ruben Meerman at TEDxQUT’

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Megan Bennett

A-Level student currently studying Biology, Chemistry and Psychology. Hoping to work within the biochemical industry as a research scientist.
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