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When we lose weight, where does it go?

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Re: When we lose weight, where does it go?

#81

Post by ncmncm »

TheOtherHobbes wrote: post #69
astrophysician wrote: post #4

> The most common misconception by far, was that fat is converted to energy. The problem with this theory is that it violates the law of conservation of matter, which all chemical reactions obey. I mean what they're getting at must be true, we are obviously not converting 1kg of rest mass into energy but that sentence is very much not true.

There's no such thing as "conservation of matter." There's conservation of mass in basic chemistry, but it's really just a partial understanding of conservation of energy anyway. It's almost as if the author has never heard of exothermic chemical reactions.

In biology, there is conservation of matter. Geology, too. Everywhere, really, except in atom-smashers, stellar cores, and nukes.

Re: When we lose weight, where does it go?

#82

Post by mncharity »

adatavizguy wrote: post #38

Likewise, where does that tree in your backyard come from? It is the product of carbon dioxide and water. edit: The significance of this thought is when a child is asked where a tree or plant comes from, at least in the US, they inevitably answer the ground when the answer should be rain that falls from the sky and air. With the naive notion a tree comes from the ground we miss the obvious which is the ground doesn't…

One fun variant of this story is: A tree is made of CO2 from air, water and minerals from the ground, and sunlight. If that wood is burned in a campfire, you get back CO2 in air, and water as vapor, and minerals as ash, and (some of) the sunlight as redder light and heat.

A related common misconception is to forget that plants, like us and most life, burn carbohydrates to CO2. Rainforest trees for instance, are only net consumers of CO2 for a couple of hours around noon.

I'd like to see science education content that weaves stories like this into a coherent tapestry. A rough-quantitative tapestry. Enabling transferable understanding. But we're a long long way from that. If anyone knows of a community pushing in that direction, I'd love to hear of it.

Re: When we lose weight, where does it go?

#83

Post by kmm »

TheOtherHobbes wrote: post #69
astrophysician wrote: post #4

> The most common misconception by far, was that fat is converted to energy. The problem with this theory is that it violates the law of conservation of matter, which all chemical reactions obey. I mean what they're getting at must be true, we are obviously not converting 1kg of rest mass into energy but that sentence is very much not true.

There's no such thing as "conservation of matter." There's conservation of mass in basic chemistry, but it's really just a partial understanding of conservation of energy anyway. It's almost as if the author has never heard of exothermic chemical reactions.

Conservation of matter is as exact a law as they come in chemistry, let alone biology. The part of mass lost as heat doesn't even match up one part in a billionth. As soon as it becomes relevant, you're not doing chemistry anymore, you're doing physics.

I know it's not "technically" correct, but when doing science, you use the laws applicable to whatever field you're working in.

Re: When we lose weight, where does it go?

#84

Post by kmm »

hprotagonist wrote: post #5

https://www.bmj.com/content/349/bmj.g7257 Meerman, R., & Brown, A. J. (2014). When somebody loses weight, where does the fat go? BMJ, 349(dec16 13), g7257–g7257. https://doi.org/10.1136/bmj.g7257 >Our calculations show that the lungs are the primary excretory organ for fat.

The survey in that study always left me with some complicated feelings. How is it possible that 100% of family doctors get this wrong, and what does this mean for their core competencies?

Don't get me wrong, I'm humble enough to understand they know infinitely more than I do, and I respect that their education and experience makes them completely capable of doing their job. But then how can they miss such a trivial understanding of how the human body works. It just doesn't match up.

Re: When we lose weight, where does it go?

#85

Post by [deleted] »

mncharity wrote: post #82
adatavizguy wrote: post #38

Likewise, where does that tree in your backyard come from? It is the product of carbon dioxide and water. edit: The significance of this thought is when a child is asked where a tree or plant comes from, at least in the US, they inevitably answer the ground when the answer should be rain that falls from the sky and air. With the naive notion a tree comes from the ground we miss the obvious which is the ground doesn't…

One fun variant of this story is: A tree is made of CO2 from air, water and minerals from the ground, and sunlight. If that wood is burned in a campfire, you get back CO2 in air, and water as vapor, and minerals as ash, and (some of) the sunlight as redder light and heat. A related common misconception is to forget that plants, like us and most life, burn carbohydrates to CO2. Rainforest trees for instance, are only…

[deleted]

Re: When we lose weight, where does it go?

#86

Post by luhn »

function_seven wrote: post #10
kevinpet wrote: post #6

Earlier quoted context omitted.

Agreed. It's the most pedantic claim I've seen on the internet all of 2020. By that logic sugar and gasoline don't get converted to energy either. Edit: actually, this is the worst article I've read on the internet in all of 2020.

I think it's the opposite of pedantic. They're asking "where" the weight goes. It does not transmutate into motion. The weight has to go somewhere. Pee, poo, breath, sweat, snot, earwax, hair, nails, spit? I assumed the CO2 we exhale would be the largest portion, and the article backs that up.

But mass can be converted into energy. Obviously that's not the primary weight loss driver (what a metabolism that would be!), but it certainly doesn't break the laws of physics.

EDIT: Because I was curious, I did the math.

Assuming diet of 2000kCal per day.

2000kCal / 3500kcal/lb fat = 0.5714 lb fat = 0.259kg fat

0.259kg = 2.329×10^16 joules = 5.556megatons of TNT

5.556megatons/day / 24 hours / 60 minutes / 60 seconds = 0.000064megatons/second = 64 tons of TNT per second

Less than I thought actually, but not someone you'd want to hang out with.

Re: When we lose weight, where does it go?

#87

Post by hprotagonist »

kmm wrote: post #84
hprotagonist wrote: post #5

https://www.bmj.com/content/349/bmj.g7257 Meerman, R., & Brown, A. J. (2014). When somebody loses weight, where does the fat go? BMJ, 349(dec16 13), g7257–g7257. https://doi.org/10.1136/bmj.g7257 >Our calculations show that the lungs are the primary excretory organ for fat.

The survey in that study always left me with some complicated feelings. How is it possible that 100% of family doctors get this wrong, and what does this mean for their core competencies? Don't get me wrong, I'm humble enough to understand they know infinitely more than I do, and I respect that their education and experience makes them completely capable of doing their job. But then how can they miss such a trivial u…

“well, they had really heavy boots!”

Re: When we lose weight, where does it go?

#88

Post by qw3rty01 »

smoyer wrote: post #41

I've been trying to exercise more (now that my foot is healed and it's easy to sit at home for way too long) ... now I'm sad to hear that I'm causing global warming.

Breathing out CO2 is not a factor contributing to global warming because it's carbon that's already in the carbon cycle.

Re: When we lose weight, where does it go?

#89

Post by divbzero »

mncharity wrote: post #82
adatavizguy wrote: post #38

Likewise, where does that tree in your backyard come from? It is the product of carbon dioxide and water. edit: The significance of this thought is when a child is asked where a tree or plant comes from, at least in the US, they inevitably answer the ground when the answer should be rain that falls from the sky and air. With the naive notion a tree comes from the ground we miss the obvious which is the ground doesn't…

One fun variant of this story is: A tree is made of CO2 from air, water and minerals from the ground, and sunlight. If that wood is burned in a campfire, you get back CO2 in air, and water as vapor, and minerals as ash, and (some of) the sunlight as redder light and heat. A related common misconception is to forget that plants, like us and most life, burn carbohydrates to CO2. Rainforest trees for instance, are only…

Yet another angle on the same story: The oxygen that makes this cycle possible wasn’t always available on Earth. It was the cycle itself (specifically photosynthesis in microbes) that created our oxygen rich atmosphere. [1]

I’ve heard of Big History [2] as one effort to weave lessons into a coherent tapestry. Agreed that this is a great way to learn.

[1]: https://en.wikipedia.org/wiki/Great_Oxidation_Event

[2]: https://www.bighistoryproject.com/home

Re: When we lose weight, where does it go?

#90

Post by function_seven »

luhn wrote: post #86
function_seven wrote: post #10

Earlier quoted context omitted.

I think it's the opposite of pedantic. They're asking "where" the weight goes. It does not transmutate into motion. The weight has to go somewhere. Pee, poo, breath, sweat, snot, earwax, hair, nails, spit? I assumed the CO2 we exhale would be the largest portion, and the article backs that up.

But mass can be converted into energy. Obviously that's not the primary weight loss driver (what a metabolism that would be!), but it certainly doesn't break the laws of physics. EDIT: Because I was curious, I did the math. Assuming diet of 2000kCal per day. 2000kCal / 3500kcal/lb fat = 0.5714 lb fat = 0.259kg fat 0.259kg = 2.329×10^16 joules = 5.556megatons of TNT 5.556megatons/day / 24 hours / 60 minutes / 60 secon…

Mass cannot be changed into energy. Maybe it can down the hall in Mr. Einstein's physics class, but here in my nutrition class we will not violate the classical laws of the universe.
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