When we lose weight, where does it go? (2018) | Hacker News Reader

When we lose weight, where does it go? (2018)

theconversation.com

14 pointsTomte15 comments

> 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.

There is no "law of conservation of matter". Chemical reactions can and do release (or absorb) energy. What is conserved is mass, with the understanding that energy and mass are interconvertible (E = mc^2).

From TFA, in case you were wondering:

> If you lose 10kg of fat, precisely 8.4kg comes out through your lungs and the remaining 1.6kg turns into water. In other words, nearly all the weight we lose is exhaled.

Ok. So fat is actually water. Then if i drink less water i will loose weight.

Yes, but water weight wont hold

No ! Fat is obviously air, you should breath less instead

But each expired breath is saturated with water vapor. Does the 8.4 Kg out of the lungs include that water vapor, or is the expired water vapor a large proportion of the 1.6 kg of water produced?

It's probably more accurate overall to say that all our weight-loss gets expired into the atmosphere as gases, with the exception of some minerals which get excreted in feces and urine.

The people saying "energy" do in fact mean CO2 and water,which are by-products of respiration (ie., literally burning fat). CO2 and water are much more stable and thus you produce energy (heat) as a by-product.

Sure, if you're accounting for mass, then yes, by mass the fat turns into the respiration by-products of water and carbon dioxide by the vast majority with a small (miniscule) amount of the mass lost to energy (the rest-mass energy contained in the carbohydrate's chemical bonds are much much smaller than the rest mass energy of the nuclei of the atoms which of course do not transmute).

I mean, i wouldn't really blame people when they say "energy"; because the point of cellular respiration is to produce energy.

Fat is metabolised to turn ADP into ATP which is used by the body in all sorts of thing and the byproduct of it is CO2 and water. Fat is a "store of energy" for this reason... but being strict; yes, this process produces energy, CO2 and water which is then expelled.

Interestingly, people also don't really know much about how plants "eat". Plants don't "eat" the sun energy; they use this energy to produce sugar that is then processed by the mitochondria just like we do. So efficient and beautiful!

Mostly we lose weight though the lungs. I found this biochemistry talk on the topic of breathing and weight loss highly informative:

https://youtu.be/nM-ySWyID9o

I found this Australian talk on the topic of breathing and weight loss highly informative:

https://youtu.be/nM-ySWyID9o

No wonder folks report feeling lighter after a long hike!

When the fuel in my car is consumed, where does it go?

Urine, and to a lesser extent perspiration. Where else?

According to the article and what I seen many other places, most of it goes out as carbon dioxide when you exhale.

This is correct

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