As the title says, I am curious if the difference between the total weight of all the food I take in during a week, and all the excrement and urine (and sweat) I release in a week would add up to the total difference in the weight of my person from the start and end of that cycle.


  • Try reddit.com/r/askscience. – Noumenon Mar 15 '15 at 10:50
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    So you think the wood that went in the fire would equal the weight of the ash? – paparazzo Mar 16 '15 at 2:34

You're not the first to wonder that, have a read of Santorio Santorio page :-)

To quote Wikipedia:

For a period of thirty years Santorio weighed himself, everything he ate and drank, as well as his urine and feces. He compared the weight of what he had eaten to that of his waste products, the latter being considerably smaller because for every eight pounds of food he ate, he excreted only 3 pounds of waste.

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    Rather than supplying just a link, you really should explain your answer. – rrirower Mar 15 '15 at 14:57

You exhale about 0.4 pounds of carbon atoms each day, which you can't keep track of. See also https://physics.stackexchange.com/questions/2605/how-does-mass-leave-the-body-when-you-lose-weight .

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    This is excellent, but I'm awarding the answer to the fellow who actually linked an empirical study that was done :O – M2tM Mar 24 '15 at 6:24

If you weighed all of your food during a week you would be normal.

If you weighted all of your collected excrement, urine and sweat* you have bigger issues than a physical fitness regime could help with.

* "And blood, don't forget blood" enter image description here

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