I’ve heard you literally poo and wee it out
In: Biology
Some, yes. Significantly you will burn it for energy producing carbon dioxide as a result, and then you will exhale that CO2. Other results of burning fat include water, which you might pee out, but it could also be exhaled since your breath is moist.
You’ve heard wrong. Almost none of the fat leaves your body through urine or feces.
You breathe it out.
Your body converts stuff into energy by reacting it with the oxygen you breathe. The stuff we eat is almost entirely made out of carbon and hydrogen, with a bunch of other elements thrown in the mix in low amounts. Your body gets energy from the carbon and hydrogen by extracting energy from them as they react with oxygen to turn into carbon dioxide and water.
That description is very simplified, but it does accurately describe the end results of metabolizing the food you eat or fat that was already present in your body.
You may have noticed that taking a fuel that has a bunch of carbon and hydrogen and lighting it on fire does the same thing. The fuel turns into carbon dioxide and water and releases the energy that you see and feel as heat. When people talk about burning calories or burning fat, that’s a metaphor, of course, but it actually isn’t that far from the truth.
Fat is converted into energy which is then released as CO2 and H2O. Most of it gets expelled by breathing, the rest by sweating and urinating.
It’s roughly the same as losing weight from your car’s gas tank, except it’s triglycerides – fat – rather than (very similar) hydrocarbons. It’s “burned” by your metabolism, creating energy, CO2 and H2O plus a bunch of minor waste products that your kidneys etc. hopefully take care of.
When you lose 10 kg, 8.4 kg comes out of your lungs (i.e. you breath it out as CO2) and 1.6kg comes out as water
Ruben Meerman (better known to Aussie kids as the Surfing Scientist) gave a great and engaging talk on this
[https://www.youtube.com/watch?v=nM-ySWyID9o](https://www.youtube.com/watch?v=nM-ySWyID9o)
When you lose weight, it gets converted into water and carbon dioxide.
Water leaves partly through your lungs as water vapor and partly through your skin as sweat and a small amount as pee.
CO2 leaves entirely through your lungs when you breathe out.
None of your weight leaves as poo.
Did you know some reptiles being cold blooded eat maybe only once a week, so being warm blooded means we can live in more areas at the cost of having to eat every day. I think fat leaves the body from just being used up.
Fat is made up of long carbon chains. Energy the body uses for work is made when you use up a carbohydrate (ex. A molecule of glucose, broken down from stored fat) and create molecules of ATP (the stuff used as energy) and waste products like CO2 (the carbon portion) and water. The CO2 leaves by breathing out.
Poo is generally made up of broken down red blood cells and things we can’t digest (among other stuff like bacteria) and pee is mainly water and ammonia (with other things like potassium).
An interesting factoid is that the fat cells never leave, only their contents. That may be one reason why it is so easy to quickly regain weight after losing it.
In this specific context, think of your body like a fireplace and chimney.
The fat is wood. Your metabolism is the fire. The fat burns and leaves behind smoke (the byproducts). That smoke exits through your lungs and out your nose/mouth (all together, the chimney).
This is oversimplified, but a good way to picture it.
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