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When we lose weight, where does it go?

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Re: When we lose weight, where does it go?

#121

Post by thaumasiotes »

ncmncm wrote: post #79
thaumasiotes wrote: post #56

Earlier quoted context omitted.

> But the most basic, predominate mechanism is that you're literally burning carbon and exhaling CO2. Well, again, you're burning oil (or if you're starving, meat), not carbon. It's mostly carbon by mass, but not by molarity.

Most of the energy is from re-binding the carbon from protons to oxygen. Binding two protons to an oxygen yields a lot less.

This is a fair point, but, prompted by the headline, I was thinking of this as a waste disposal problem, not as a "how much energy can I get out of a pound of fat?" problem.

Re: When we lose weight, where does it go?

#122

Post by ncmncm »

vagrantJin wrote: post #109
ncmncm wrote: post #95

Earlier quoted context omitted.

If they did, there would not be a huge industry in removing heavy metals from industrial wastewater before flushing to municipal sewer systems.

You make it sound like a conspiracy.

It's only a conspiracy if it is against the law.

Re: When we lose weight, where does it go?

#123

Post by doublesCs »

evanb wrote: post #66
astrophysician wrote: post #4

> The most common misconception by far, was that fat is converted to energy. The problem with this theory is that it violates the law of conservation of matter, which all chemical reactions obey. I mean what they're getting at must be true, we are obviously not converting 1kg of rest mass into energy but that sentence is very much not true.

Chemical bonds are on the scale of eV---the cost to liberate an electron from a hydrogen atom is 13.6eV, for example. So the best you can hope for, in a chemical reaction, is a change in mass of the scale of 10s of eV / c^2. In comparison, a single proton weighs 938 MeV = 9.38e+8 eV. So the fraction of the mass that is converted into energy is on the scale of 1e-7.

This is the correct answer.

There's no such thing as conservation of mass, mass and energy are convertible into each other. But in the real of chemistry that conversion happens on a ratio of at most 1e-7, so when it comes to the human body we might as well say that the weight that goes in must equal what comes out, and that's close enough.

Re: When we lose weight, where does it go?

#124

Post by doublesCs »

ncmncm wrote: post #81
TheOtherHobbes wrote: post #69

Earlier quoted context omitted.

There's no such thing as "conservation of matter." There's conservation of mass in basic chemistry, but it's really just a partial understanding of conservation of energy anyway. It's almost as if the author has never heard of exothermic chemical reactions.

In biology, there is conservation of matter. Geology, too. Everywhere, really, except in atom-smashers, stellar cores, and nukes.

No, this isn't true. There's no conservation of matter anywhere. If you take 2 hydrogen atoms and weight them, then bond them together in a hydrogen molecule and weight that, the molecule weights less than twice one hydrogen atom.

Re: When we lose weight, where does it go?

#125

Post by tamcap »

ncmncm wrote: post #80
tamcap wrote: post #48

The story is (likely purposefully) ignoring some other ways you can "lose weight/energy" from your body. But I am curious what would the complete list be... * heat (the most obvious one, not explicitly mentioned I guess?) * even in healthy humans, some fatty acids are excreted with bile into the gut and subsequently removed via feces * if you are fasting (or in ketosis, such as via keto diet) you will exhale / sweat…

Heat does not carry away a measurable amount of weight.

You are right. While the energy of the chemical bonds is converted into heat, it's not like the bonds itself have any weight. It's a pretty obvious statement.

Now I am embarrassed! :)

Re: When we lose weight, where does it go?

#126

Post by ncmncm »

doublesCs wrote: post #124
ncmncm wrote: post #81

Earlier quoted context omitted.

In biology, there is conservation of matter. Geology, too. Everywhere, really, except in atom-smashers, stellar cores, and nukes.

No, this isn't true. There's no conservation of matter anywhere. If you take 2 hydrogen atoms and weight them, then bond them together in a hydrogen molecule and weight that, the molecule weights less than twice one hydrogen atom.

But you still have the two hydrogen atoms, before and after. They are matter. Tiny (really tiny!) differences in weight don't change that.

Re: When we lose weight, where does it go?

#127

Post by doublesCs »

ncmncm wrote: post #126
doublesCs wrote: post #124

Earlier quoted context omitted.

No, this isn't true. There's no conservation of matter anywhere. If you take 2 hydrogen atoms and weight them, then bond them together in a hydrogen molecule and weight that, the molecule weights less than twice one hydrogen atom.

But you still have the two hydrogen atoms, before and after. They are matter. Tiny (really tiny!) differences in weight don't change that.

I guess when you said "conservation of matter" I interpreted that as meaning "conservation of mass", seeing as we're talking about weight loss.

Re: When we lose weight, where does it go?

#128

Post by doublesCs »

doublesCs wrote: post #123
evanb wrote: post #66

Earlier quoted context omitted.

Chemical bonds are on the scale of eV---the cost to liberate an electron from a hydrogen atom is 13.6eV, for example. So the best you can hope for, in a chemical reaction, is a change in mass of the scale of 10s of eV / c^2. In comparison, a single proton weighs 938 MeV = 9.38e+8 eV. So the fraction of the mass that is converted into energy is on the scale of 1e-7.

This is the correct answer. There's no such thing as conservation of mass, mass and energy are convertible into each other. But in the real of chemistry that conversion happens on a ratio of at most 1e-7, so when it comes to the human body we might as well say that the weight that goes in must equal what comes out, and that's close enough.

Typo. *in the realm of chemistry

Re: When we lose weight, where does it go?

#129

Post by scared2 »

qw3rty01 wrote: post #91
scared2 wrote: post #68

This just makes me think that one of the main source of global warming is human population ( as co2 producers).

Exhaled CO2 is in equilibrium with plants inhaling CO2 to provide us food, so exhaling isn't considered a factor in global warming.

But you need large number of plants to make it in equilibrium. Currently rate if deforestation is in par with global population growth
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