How Does Fat Actually Leave The Body? Where Does It Go?

Fat loss is often misunderstood, with many believing it simply “vanishes” through exercise, is simply excreted in solid form in the bathroom, or materially disappears when converted for energy. However, the principle of conservation of mass plays out here, in that the mass in fat doesn’t disappear—it changes its arrangement:

In and out

Fat is composed of carbon, hydrogen, and oxygen atoms, with an example common form of fat in the body being C₅₅H₁₀₄O₆. That’s a lot of Cs and Hs, and a few Os.

When fat leaves the body, it has been primarily converted into carbon dioxide (CO₂) and water (H₂O).

According to a 2014 study by the University of South Wales, 84% of the mass of fat exits the body as CO₂ exhaled through breathing, while 16% leaves as water through sweat, urine, and other bodily fluids (all of which contain H₂O).

You’ll notice there are a lot more Os going out, proportionally, than we originally had in the C₅₅H₁₀₄O₆. For this reason, the process requires oxygen intake; for every 10 kilograms of fat burned, by simple mathematics the body needs around 29 kilograms of oxygen.

Physical activity plays a crucial role in fat loss. When the body exerts itself, it naturally switches to a higher oxygen metabolism necessary for fat breakdown. This effect is amplified during intermittent fasting, which boosts human growth hormone (HGH), a hormone that aids in fat metabolism.

However, simply hyperventilating won’t work; exercise is essential to activate these processes—otherwise it’s just a case of oxygen in, oxygen out, without involving the body’s chemical energy reserves.

Consequently, one of the best diet-and-exercise combinations for fat loss is intermittent fasting with high-intensity interval training.

And, as for what to eat, this video says raw vegan, but honestly, that’s not scientific consensus. However, a diet rich in unprocessed (or minimally processed) fruits and vegetables definitely is where it’s at, with the plant-heavy Mediterranean diet generally scoring highest—which can be further improved by skipping the mammals to make it pesco-Mediterranean. Current scientific consensus does not give any extra benefits for also omitting moderate consumption of fish and fermented dairy products, so include those if you want, or skip those if you prefer.

For more on all of this, enjoy:

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Want to learn more?

You might also like to read:

Are You A Calorie-Burning Machine? (Calorie Mythbusting)

Take care!