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Comment by peterldowns | Hacker News Reader

A related fun fact is that you generally lose weight by exhaling, generally while you sleep. Sweating, defecating, etc. is all temporary. If you're trying to lose weight, make sure you're sleeping enough!

edit: see my followup comment, didn't mean to mislead here. I'm not a scientist and sleep and food science is both pretty hard to trust.

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Why would you lose more weight with exhalations from relatively low sleeping metabolism than being awake? Not being contrary, genuinely curious.

If I were to guess, the metabolism generates waste during activity that gets processed and exhaled as CO2 during sleep.

Bad guess, I am not sure what OP really intends (perhaps you don’t consume whilst you sleep?!) because as you probably are starting to remember from primary school your body maintains homeostasis by continually respiring. It doesn’t suddenly decide to take a dump.

Ok, it does, but even when it does that, in order to do that it has been continually maintaining homeostasis

Doesn't the CO2 get exhaled during activity rather than sleep?

You exhale more CO2 during activity because metabolism increases. Burning glucose and fat produces CO2.

It doesn't make sense that you would lose more weight by sleeping only considering metabolism.

I can see an argument around sleeping always being a net loss, since you're never consuming food while sleeping. Sleeping more thus means you may eat less.

Sorry, my phrasing was not clear. Your metabolic rate is generally lower during sleep than during the day; you definitely lose more weight overall during the day than while asleep. But, while you're sleeping, you don't eat anything. And quality sleep is necessary to maintain overall metabolic function. I'm not a scientist and didn't mean to make any strong claims!

Two short articles I was basing this off of:

- "When somebody loses weight, where does the fat go?" https://www.bmj.com/content/349/bmj.g7257

- "Sleep and Metabolism: An Overview" https://pmc.ncbi.nlm.nih.gov/articles/PMC2929498/

Isn't the main reason because you're not eating?

Yes. Sleep by itself does nothing unique. In fact, you have a slightly lower rate of metabolism than even the "basal" metabolic rate.

Eh? That isn't right. The metabolic rate while asleep is even lower than the basal average. The only reason there's a net loss after sleep is because you're not regularly consuming food or water as you would when you're awake, not anything special about sleeping by itself. You're burning fewer calories than usual at that time!

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