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I'd like to get some clarification on specifically how the matter from the fat reserves of the Adipocyte physically leaves the body.

In other words, if you were to somehow follow every atom in the fat reserves of the cells of a dieting person, then, via what hole would these atoms ultimately exit the body?

Is the answer to this question merely "exhaling through the mouth"? Or do they come out in feces too?

Note 1: This question is not to be confused with the question: "How does mass leave your body in general?" For there are several ways to accomplish this. (e.g. shedding skin cells, cutting off your arm, cutting your hair, sweating, dehydration, liposuction, bleeding, spitting, blowing your nose, etc...)

Note 2: Please see this other similar StackExchange post here:

How Does Mass Leave the Body When you Lose Weight?

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migrated from Sep 8 '13 at 7:41

This question came from our site for active researchers, academics and students of physics.

up vote 3 down vote accepted

Yes, they are mostly exhaled. The carbon, hydrogen and oxygen that the fats are made of recombine to become $CO_2$ and $H_2 O$ and are exhaled.

It's the same overall chemical reaction as if the fats / carbohydrates were burnt, except it's by a different pathway, and the energy produced goes (mostly) towards driving other chemical reactions rather than becoming light and heat.

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Hi thanks. Can you clarify the "mostly" part? Where else would they exit besides the mouth? – tdog2 Sep 8 '13 at 15:49
@tondog Some of the $H_2 O$ will come out in urine or sweat, for example. – Nathan Reed Nov 3 '14 at 23:13

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