Eli5: When you go to sleep weighing a certain amount and wake up weighing less. Where did that weight go?
In: Biology
You breath it out.
You breath in air that is about 20% Oxygen. That oxygen is used up by your body and when exhaled, has an extra Carbon atom attached (CO2).
There’s two main sources of weight loss.
Any fat/carbohydrate burning done (by your metabolism to keep you alive if nothing else) will create CO2 and H2O vapor, and breathing it out will be fat/carbs that are no longer weighing you down.
Your body is constantly using water for a number of other things as well, and as that water evaporates/is wicked off by your bedding, it is (water) weight lost.
Everyone saying you breathe out enough carbon dioxide in 7 hours to make a difference on the scale is hilariously wrong. This is a very negligible amount. You shed off more weight from exfoliating hair and skin cells overnight than you do from exhaling.
The primary weight loss is via water loss from sweating
You breathe out carbon dioxide. That is actually the main way of losing weight, even when exercising.
The other thing is losing water. You constantly lose a little bit of water with breathing and sweating. And you don’t replenish when you’re asleep.
In just one night? From sweating. If you lose weight over a long time, it is because your metabolism converts fat into co2 which you breath out
the people saying that you lose weight through breathing are absolutely not trolling. they are correct. in fact, the only way you can lose weight permanently is through breathing, by expelling CO2. but the reason permanent weight loss is difficult and slow is because it takes a while for all that CO2 that you expel to add up to a significant amount. but that is the mechanism by which weight loss is achieved.
other types of shedding body mass are significant, yes, as others have pointed out. you can easily lose kilograms worth of water weight in not more than a few hours through intense exercise. but all that weight will be gained back when you rehydrate. the same with urinating/defecating. you only pee what you drink (some of it), and you only poop what you eat (some of it), so to pee 200g worth of piss, you had to have drank 200g of water beforehand, the same with poop, so these forms of weight “loss” aren’t actually losses, they are just fluctuations around a constant level.
hair/skin shedding also follows a similar logic. if you shed some hair, your body will accumulate some nutrients and grow it back, the same with skin, so the net weight of those on your body remains roughly the same.
but it is correct that if you lose quite a bit of weight on only one night, most of that loss probably came through water loss. which will be recuperated as soon as you drink water.
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