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Comment by SigmundA | Hacker News Reader

Fun thing about the carbon cycle, much of the candles mass goes into the air and much the mass of a tree comes from the air.

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My mind was blown a little bit when I realized that when you lose fat, you do so by breathing it out. Some of which will also go on to make trees as well.

But there’s also water generated when buying (edit:burning) carbo hydrates.

I assume you mean burning, but if you drive or even walk to the store to buy the carbs that also generates water.

The final bit that locked it in for me (and someone please correct me if this is wrong) is that going to the bathroom (which what many people assume is where weight leaves the body) is actually the last stage of "energy input" to the body and doesn't really play a role in "energy output".

Well, your body does not utilize all the energy it could from the food and drink you ingest. Say if you get a condition where your digestive efficiency goes down - tapeworm, inflammation, whatever - all else equal, you're going to start losing weight fast. This is why gastric bypass surgery works.

I don't understand what you are saying here. The physical weight of the feces does leave your body. How is that an input?

It's the end of the input. Think about it another way... say you chew on a slice of orange, swallow the juice, and spit out the pith. The pith isn't output of your body. It's just the end of the intake process.

Feaces isn't produced by your metabolic system. It's just the byproduct of intake. The stuff that your body didn't absorb.

Feces may not be produced by your metabolic system, but it is certainly not just a byproduct of intake. It includes red blood cells that have failed quality assurance and been filtered out of the bloodstream by the spleen; that is why it's brown.

Not long ago I googled why shit and piss are two things and not one. It just suddenly seemed odd to me one day. The answer seemed to be that the stuff we poo out never goes 'inside' our body. Imagining our bodies being like a tube or doughnut, what goes in our mouths just goes through the hole, staying in a sense on the outside. What comes out is just what we couldn't use as it passed along the conveyor belt. Piss, on the other hand, is the waste from (truly) inside us.

Hmm seems there are (at least) two levels of 'inside' here. It's quite a weird, topological subject hehe. It seems odd that we don't intuitively think of those as different degrees of insideness.

Therefore, trees are fat.

;)

Cheekily, this also means that if you're losing weight, you are a net emitter of CO2, thus hastening global warming. On the other hand, if you gain weight, you are a net sink.

Of course the carbon cost of food production does… complicate this a little bit :)

The balance evens out pretty quickly on the other end though. Does anyone know if crematoriums do carbon capture?

IIRC, you urinate a decent chunk of it out too.

Hey snap! I just posted the same thing before I read your post!

"Where do trees get their mass?" - https://www.youtube.com/watch?v=2KZb2_vcNTg

This was highly enlightening the first time I watched it :)

> much the mass of a tree comes from the air

A fun pastime of mine is asking people where they think the mass of a tree comes from and trying to guide them to the right answer (CO2) via the socratic method (i.e. trying to only ask questions)

I was wondering how much of a tree's mass is not Carbon or Oxygen. Turns out it's somewhere around 10%; half of that is light weight hydrogen. So water probably provides a decent chunk of a tree's oxygen content also.

Page 4 https://www.urban-forestry.com/assets/documents/Coder_Tree%2...

I also love the idea that when you exercise more and lose weight, you shed the body mass by breathing out co2.

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