Related study, which I found interesting, that confirms the weight you “lose” is excreted primarily through your breath:

https://www.medicalnewstoday.com/articles/287046#Tracking-th...

What I find most interesting is that so many people, including those with supposed expert knowledge of physiology, get this totally wrong.

On the flip, that tree in your backyard isn't growing out of the ground outside of the moisture that falls from the sky -- if it did the ground would sink -- it is growing out of the air.

A good demonstration of this by Ruben Meerman: https://www.youtube.com/watch?v=vuIlsN32WaE

Yep! When you lose weight you slightly increase the mass of the atmosphere by roughly the amount you lost. Whatever doesn't go into the atmosphere goes into the toilet (mostly water).

I 'discovered' this as a teenager because my weight in the morning would be lower than my weight at night and I had done nothing but lie in bed comfy all night. There was only one place it could reasonably go - now that I wasn't wetting my bed that is.

The amount of mass exhaled as CO2 at night is nowhere near as much as the loss through perspiration and evaporation. Water loss happens pretty much constantly and is why one dies of dehydration after a couple days.

I was curious about this. I'm on a diet now and I often weight like 0.5-0.8 kg less in the morning.

And when I go on a 20km walk on the weekend I lose about 1kg in 5 hours. Is it mostly water? Cause I drink a lot during the walk and I don't go fast enough to get sweaty.

It pretty much has to be. 1kg would be 1L of water, which is not that much to lose over 5 hours.

But 1kg of fat is 7700 kcal, which would be a massive amount of energy to expend in 5 hours. Unless your "walks" involve running uphill with a 25kg pack or something like that. :)

Short-term energy consumption on a 5 hour hike would be from stored glucose, fat breakdown IMHO would happen slower. A 20km hike can consume 1000-2000kcal depending on how hard it is (climb, terrain, weight of hiker, weight of pack matter) so that would be 0.25-0.5kg of carbs - so potentially that loss could be 50/50 carbs and water.

But hydration definitely is a big aspect of mass simply because of how much you add and lose. I once did a ~90km hike in 24 hours or so, and I believe I drank something like 15+ litres of liquids during that.

Depends on what you’ve eaten recently. It’s pretty easy to burn fat on a hike if you go while fasting.

Humans lose moisture for a variety of reasons normally, you don’t need to be sweating in order to lose it, although that obviously drives the loss rate up. You lose a ton of water through just breathing.

On your walks you’re probably burning glycogen, the carbohydrate we store in our liver and muscles for easy access energy, and exhaling a lot of water. We store about half a kilo of glycogen which is then bound up with 3-4x as much water still. While you’re not likely to consume all your glycogen in a 20km walk (you need a marathon to do it), burning a decent chunk of it on top of normal water loss isn’t an unreasonable hypothesis.

Yes. A lot of fad diets and supplements work on this principle; dehydrating you appears to lose weight really quickly initially. It's not sustainable.

The human body is darn efficient.

You would probably have to run 50-70km to lose 1kg fat.

It's easier to not eat calories than to burn them after eating.

I suppose you could also lose weight via the moisture in your breath, or sweat of operation. But yes, it’s pretty cool.

You do lose weight via the moisture, typically around 200g if this article[1] is to be trusted (doesn't cite its sources). More if you are sweating heavily for one reason or another. Much bigger effect than calories burnt in the same duration.

[1] https://washingtoncitypaper.com/article/221338/straight-dope...

how did you weigh yourself so precisely?

Its pretty common to weigh 1lb less in the morning than night, don't need a fancy scale for that. But decimal level accuracy scales are also common.

This takes surprisingly little precision, you really exhale quite a lot of mass over 8 hours.

Except the fat goes out of your body and the candle is going into your body.

I saw a study showing correlation between cognitive impairment and sub-micron particles in the air. They used candles for the study but coal factories are the large scale concern.

Related to this, I've seen research showing that by the time a room feels stuffy there is enough CO2 to measurably affect cognitive performance. Now I'm much better about remembering to open a window when I'm coding and starting to drag.

Highly recommend getting a cheap CO2 meter. We have a couple around the house. It’s amazing how fast a room fills with CO2 when cooking or having people over (pre-COVID). You can become more attuned to it — I have a pretty good idea what 800PPM feels like compared to 500PPM compared to 1000PPM. Weird party trick too.

What do they feel like for you? I’ve had a CO2 sensor in my office for a long time, and don’t think I can tell the difference between 500 and 1500ppm.

It honestly doesn’t feel like anything. I just ask my body what the number is and it’s always within a hundred ppm. it feels like a guess, but like a guess when you’ve been counting cards so long you know roughly what the count is without consciously keeping track of it? If that makes sense.

A couple of years ago, I started getting headaches. Everything in my noggin appeared normal, and one day I worked with the window open. No headache. So I got my first one, it wasn’t very expensive (€50-100 IIRC) and did some experiments. Sure enough, it would get up to 1800ppm in my tiny office and I’d get a headache.

I’d say the biggest thing it seems to affect is coding. If I can keep it below 600ppm in my office, I can code all day and late into the evening without feeling too exhausted. At about 1k, I start to feel kinda sleepy and tired after awhile.

My wife and kid had fun doing the observations and asking the questions during the experiment. Good times. We used it as a way to teach our son how to do experiments and ethics.

Do you have a recommendation for one? I heard it's quite hard to get accurate ones without paying a lot.

A quick search shows a ton of choices, Are there any models or brands you like, or dislike?

I wasn’t too picky, I ended up with tfa dostmann‘s which seemed reasonable in price point vs accuracy.

Yet another advantage of remote work! How many offices have windows you can open? (I used to work in one that did, because it was in an old mill building. It was great.)

You can breath in your burned fat too, if you wish.