3 ms·

Just write the equation like this: Energy intake - Energy expenditure - Change in energy stores = 0 There. Just f(x,y,z)=0. That's what the first law really s

by nova 17y ago

Just write the equation like this: Energy intake - Energy expenditure - Change in energy stores = 0 There. Just f(x,y,z)=0. That's what the first law really says. There is no causality implied, it just a first integral of the "motion" of metabolism that the body, naturally, has to follow. It does NOT say what variables are free to independently modify. It's just a relation the three of them have to obey.

jessep 17y ago
I'm confused by the application of this law to food. My reason: excrement. You put some mass that contains chemical energy into your body. Then that mass comes out of your body, minus SOME of the chemical energy. How much of it is extracted? What determines this? I have no idea. That said, I think it is funny to treat it as if the only way to get rid of energy is expenditure. How about: Energy intake - Energy Ependiture - Energy still in food when it comes out the other end = Change in energy stores
- nova 17y ago
  Yes you can decompose it further but it doesn't matter. Just consider that "energy intake" is the energy actually absorbed by your body, not what you put in your mouth. (Try eating grass. It has energy, but we can't use it) My point is that a lot of people misinterpret conservation of energy assigning it a direction of causality it doesn't have. It's a constraint between variables (not an assignation as in programming languages) which are under complex feedback control systems in the body, and that's why the kind of calories you eat (fats vs carbohydrates) DOES matter, you don't eat abstract pure energy but as you say mass with chemical energy that has to be metabolized. That's why starvation diets (just counting theoretical calories, which are numbers obtained in laboratories, dismissing the type of macronutrient) often fails in the long term and leave serious damage. The book talks long about this.
  - jessep 17y ago
    Right. I didn't mean to take away from your point at all, which I do think is fascinating. I've just noticed that people generally do equate "energy intake" with calories that go into your mouth, and find that interesting.

by nova 17y ago

jessep 17y ago

I'm confused by the application of this law to food. My reason: excrement. You put some mass that contains chemical energy into your body. Then that mass comes out of your body, minus SOME of the chemical energy. How much of it is extracted? What determines this? I have no idea. That said, I think it is funny to treat it as if the only way to get rid of energy is expenditure. How about: Energy intake - Energy Ependiture - Energy still in food when it comes out the other end = Change in energy stores

nova 17y ago
Yes you can decompose it further but it doesn't matter. Just consider that "energy intake" is the energy actually absorbed by your body, not what you put in your mouth. (Try eating grass. It has energy, but we can't use it) My point is that a lot of people misinterpret conservation of energy assigning it a direction of causality it doesn't have. It's a constraint between variables (not an assignation as in programming languages) which are under complex feedback control systems in the body, and that's why the kind of calories you eat (fats vs carbohydrates) DOES matter, you don't eat abstract pure energy but as you say mass with chemical energy that has to be metabolized. That's why starvation diets (just counting theoretical calories, which are numbers obtained in laboratories, dismissing the type of macronutrient) often fails in the long term and leave serious damage. The book talks long about this.
- jessep 17y ago
  Right. I didn't mean to take away from your point at all, which I do think is fascinating. I've just noticed that people generally do equate "energy intake" with calories that go into your mouth, and find that interesting.