4 ms·

Energy in/out, at least in the sense most people and your grandparent refer to, can be wrong without violating conservation of energy. E.g. if you poop out food

Energy in/out, at least in the sense most people and your grandparent refer to, can be wrong without violating conservation of energy. E.g. if you poop out food from which not all calories have been used.

wtallis 7y ago
The solution to this issue is not to start claiming things in violation of thermodynamics. Instead you should call attention to the fact that nutrition labels do not always accurately count the number of bioavailable calories ("calories in"), and that unusual circumstances can drastically change an individual's ability to extract energy from their diet. Rejecting "calories in = calories out" is a distraction from the real challenges, and has the side effect of making you sound much less scientifically credible. Edit: see this comment for an example of reasonable discussion that doesn't oversimplify to the point of contradicting basic science: https://news.ycombinator.com/item?id=20860678 https://news.ycombinator.com/item?id=20860678
- DanBC 7y ago
  It's the CICO crowd who are ignoring basic science when they claim the human body will perfectly digest food. Across time a person's ability to extract calories from food changes because their gut flora changes.
  - wtallis 7y ago
    > It's the CICO crowd who are ignoring basic science when they claim the human body will perfectly digest food. That's not at all what anyone is claiming when they say you need to run a calorie deficit to lose weight.
- beagle3 7y ago
  The thermodynamics matter only as much as they are a tautology (which means: not at all), or as an upper bound. Thermodynamics predict that you'd be better off drinking gasoline (12kcal/gr > fat's 9kcal/gr), and just as well eating wood chips (a carbohydrage) -- even though you get zero energy from either. "But we're not using calorimeter data, we're using atwater factors"; Well, those actually DO vary from person to person, IIRC as much as 50%; and other things also matter (e.g., adding activated carbon to your food will result in less energy extracted in general; using Ally would result in less energy extracted from fat). And that's just for the "calories in" part; metabolic rate can also vary as much as 80% along time and between people, depending on muscle volume, or other random, less understood factors - so without a proper measurement chamber you don't know the "calories out" either. The food labels and general activity tables serve as a good general approximation that describes probably 80% of the public quite well. But invoking thermodynamics (except as an upper bound for calories in) is not justified by our current understanding of metabolism.
  - wtallis 7y ago
    > But invoking thermodynamics (except as an upper bound for calories in) is not justified by our current understanding of metabolism. The problem is when people claim that they can lose weight without running a calorie deficit. This is what's obviously wrong, and it is completely fair to invoke thermodynamics as a way to immediately and soundly refute such claims. When someone claims to have anecdotal evidence of losing weight while not running a calorie deficit, the error is not with the "calories in = calories out" equation but with their poor accounting of where the calories are going. In my experience, people who promote their pet dieting theories (especially ones that promise dramatic weight loss without requiring exercise) using thermodynamically impossible claims are far more prevalent than people who mean lab calorimeter data when they talk about the calorie content of their food. Your comments about gasoline and wood chips are an insulting straw man, because nobody is ever referring to those numbers in a casual context. They're talking about the calorie numbers that can be found on nutrition labels, and those are meant to approximate metabolisable energy, not heat of combustion.
    - briancleland 7y ago
      > The problem is when people claim that they can lose weight without running a calorie deficit. Of course people can lose weight without running a calorie deficit. It's a commonplace experience nowadays, and absolutely trivial to demonstrate. You can test if for yourself if you are even slightly interested in checking the validity of your theories. The death of the ridiculous thermodynamic model of human nutrition can't come soon enough.
    - beagle3 7y ago
      I agree about the prevalence of pet theory, but my example wasn’t a strawman. Your thermodynamic argument involves values that you take on faith (Atwater factors) which have been shown to have 50% variance, and values like BMR that also have 50% variance. As a result, invoking thermodynamic impossibility is not justified. I agree with the gist of what you are saying - but not with the validity of the thermodynamic reasoning as proof.
      - 7y ago
bialpio 7y ago
See, I wouldn't define pooped out unused food as being "in". If you want, you can define it as "in", but then you need to also include the pooped out energy in the "out" column.
Retric 7y ago
That’s really not how food calories are defined. https://en.m.wikipedia.org/wiki/Atwater_system https://en.m.wikipedia.org/wiki/Atwater_system Now, a lot of simplification goes on and it’s true food labels are based on heathy digestion. But, that has little to do with the actual definition. PS: I think this goes back to how the description of how Calorimeter’s are used. Yes, they give a value from burning food, but that’s not the only number being considered.

wtallis 7y ago

The solution to this issue is not to start claiming things in violation of thermodynamics. Instead you should call attention to the fact that nutrition labels do not always accurately count the number of bioavailable calories ("calories in"), and that unusual circumstances can drastically change an individual's ability to extract energy from their diet. Rejecting "calories in = calories out" is a distraction from the real challenges, and has the side effect of making you sound much less scientifically credible. Edit: see this comment for an example of reasonable discussion that doesn't oversimplify to the point of contradicting basic science: https://news.ycombinator.com/item?id=20860678 https://news.ycombinator.com/item?id=20860678

DanBC 7y ago
It's the CICO crowd who are ignoring basic science when they claim the human body will perfectly digest food. Across time a person's ability to extract calories from food changes because their gut flora changes.
- wtallis 7y ago
  > It's the CICO crowd who are ignoring basic science when they claim the human body will perfectly digest food. That's not at all what anyone is claiming when they say you need to run a calorie deficit to lose weight.
beagle3 7y ago
The thermodynamics matter only as much as they are a tautology (which means: not at all), or as an upper bound. Thermodynamics predict that you'd be better off drinking gasoline (12kcal/gr > fat's 9kcal/gr), and just as well eating wood chips (a carbohydrage) -- even though you get zero energy from either. "But we're not using calorimeter data, we're using atwater factors"; Well, those actually DO vary from person to person, IIRC as much as 50%; and other things also matter (e.g., adding activated carbon to your food will result in less energy extracted in general; using Ally would result in less energy extracted from fat). And that's just for the "calories in" part; metabolic rate can also vary as much as 80% along time and between people, depending on muscle volume, or other random, less understood factors - so without a proper measurement chamber you don't know the "calories out" either. The food labels and general activity tables serve as a good general approximation that describes probably 80% of the public quite well. But invoking thermodynamics (except as an upper bound for calories in) is not justified by our current understanding of metabolism.
- wtallis 7y ago
  > But invoking thermodynamics (except as an upper bound for calories in) is not justified by our current understanding of metabolism. The problem is when people claim that they can lose weight without running a calorie deficit. This is what's obviously wrong, and it is completely fair to invoke thermodynamics as a way to immediately and soundly refute such claims. When someone claims to have anecdotal evidence of losing weight while not running a calorie deficit, the error is not with the "calories in = calories out" equation but with their poor accounting of where the calories are going. In my experience, people who promote their pet dieting theories (especially ones that promise dramatic weight loss without requiring exercise) using thermodynamically impossible claims are far more prevalent than people who mean lab calorimeter data when they talk about the calorie content of their food. Your comments about gasoline and wood chips are an insulting straw man, because nobody is ever referring to those numbers in a casual context. They're talking about the calorie numbers that can be found on nutrition labels, and those are meant to approximate metabolisable energy, not heat of combustion.
  - briancleland 7y ago
    > The problem is when people claim that they can lose weight without running a calorie deficit. Of course people can lose weight without running a calorie deficit. It's a commonplace experience nowadays, and absolutely trivial to demonstrate. You can test if for yourself if you are even slightly interested in checking the validity of your theories. The death of the ridiculous thermodynamic model of human nutrition can't come soon enough.
  - beagle3 7y ago
    I agree about the prevalence of pet theory, but my example wasn’t a strawman. Your thermodynamic argument involves values that you take on faith (Atwater factors) which have been shown to have 50% variance, and values like BMR that also have 50% variance. As a result, invoking thermodynamic impossibility is not justified. I agree with the gist of what you are saying - but not with the validity of the thermodynamic reasoning as proof.
    - 7y ago

bialpio 7y ago

See, I wouldn't define pooped out unused food as being "in". If you want, you can define it as "in", but then you need to also include the pooped out energy in the "out" column.

Retric 7y ago

That’s really not how food calories are defined. https://en.m.wikipedia.org/wiki/Atwater_system https://en.m.wikipedia.org/wiki/Atwater_system Now, a lot of simplification goes on and it’s true food labels are based on heathy digestion. But, that has little to do with the actual definition. PS: I think this goes back to how the description of how Calorimeter’s are used. Yes, they give a value from burning food, but that’s not the only number being considered.