## Food Mass

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Generic Goon
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### Food Mass

Maybe someone on these forums can help me out. I was wondering, when your body turns food into energy, is mass lost or does it stay conserved? I ask because I have heard that a significant amount of the mass was turned into energy, but I have also heard that even if you get energy from a chemical reaction, you only actually lose mass after nuclear reactions.

thoughtfully
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### Re: Food Mass

There isn't a seperate conservation law for mass and energy, there is only one. Mass is energy. They are the same thing, expressed in different units. (the conversion formula: E=mc2) Unless its a truly humongous amount of energy, you won't notice the loss of mass, but it's still there.

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douglasm
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### Re: Food Mass

Mass is lost in the production of energy by the body, but it is such a tiny amount that even the best equipped labs on Earth probably wouldn't be able to measure it.

Essentially, any process that produces energy, no matter what its nature, consumes mass. No matter what its nature, the amount of mass consumed is governed by Einstein's famous equation, E = mc2. The only thing remarkable about nuclear reactions compared to chemical reactions in this respect is the sheer amount of mass converted and energy produced.

thoughtfully
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### Re: Food Mass

Mass isn't "consumed", the entire system will weigh the same before and after whatever reaction being considered occurs. You have to count the escaping energy, just as you would escaping gasses.

Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.
-- Antoine de Saint-Exupery

Tass
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### Re: Food Mass

But of course way more mass is lost the regular way in the form of breathing in O2 and breathing out CO2, (plus evaporation of water).

These will dwarf any mass given of in the form of energy.

Yakk
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### Re: Food Mass

We can extract about 8 kiloCalories of energy from a gram of fat.

This comes to 3.72426227 × 10^-13 kg, or a fraction of about 1/3 * 10^-9 of the mass of the fat.

Now, our body doesn't store this mass as "raw energy" (there is no such thing), but rather in the chemical bonds of other chemicals in our body, or just by storing the fat itself.

So chemical reactions can change the mass of a chemical, but it is such a small amount that we cannot detect it practically -- we only know it happens because it would be a very inconsistent world if it didn't!

What our body does with food is it uses the chemical energy in it to build up local energy sources (and sometimes just breaks it down into raw materials, then imports those raw materials). We then store it in proteins, fats, sugars, and temporary energy storage molecules of various kinds. When we use energy, we break down those chemicals in order to fuel ourselves.
One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision - BR

Last edited by JHVH on Fri Oct 23, 4004 BCE 6:17 pm, edited 6 times in total.

thoughtfully
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### Re: Food Mass

Death, taxes, and entropy. The 2nd Law takes his cut, too. A lot of that energy becomes heat.

Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.
-- Antoine de Saint-Exupery