The ISS is constantly losing gas, I believe that the primary source of new O2 is actually electrolysis of water, not pressurized tanks, but that they do also have pressurized tanks as a backup.
A person breathes out roughly 1kg of CO2/day, and it follows you breathe in about the same amount of O2, not an impossible amount of mass to resupply.
which is crazy low if you put it in perspective and see that (gas powered) cars release about 0.2 kg of CO2 ... per kilometer.
There's a reason all the old buildings in big cities are elevated a few steps above street level...
So... Only about one chocolate bar per km.
Also ... CO² is bad ... but at least is non-toxic compared to some of the other side products.
https://www.bts.gov/statistical-products/surveys/national-ho...
I've heard that you mostly love weight by breath, and wondered what was the actual limit. Thanks for that info.
Also... this is a typical number for a typical lifestyle, I believe it can vary substantially if you exercise a lot.
Also... I know nothing about wait loss, but surely a lot of the mass is in water?
The numbers are in the right ballpark.
Not really. Yes, you loose water (and its weight) when you e.g. sweat a lot when exercising, but it gets replaced when you drink. More generally your body keeps the amount of water more or less at the same level through intake (drinking, but also water in food), urinating and sweating. There are short-term variations, but besides exceptional circumstances on a day-to-day basis the amount of water in your body should be pretty constant.
Real weight loss is through loss of muscles (not preferable) or loss of fat.