4 ms·

When considering just the energy balance, calories aren't an approximation. You see, energy is what we call a state function, it depends only on the state of th

by kmm 10y ago

When considering just the energy balance, calories aren't an approximation. You see, energy is what we call a state function, it depends only on the state of the system and not how we got there. The catabolism of lipids, sugars and proteins into carbon dioxide, water and urea is an extremely complicated process, which I'm not sure we've even completely mapped yet. Last time I counted, the oxidation of glucose in our body takes about 33 steps. However, because we know the difference in energy (actually enthalpy but let's not split hairs) between the input and the output, we know the exact total amount of energy released in all those steps. And it has to be exactly the same as the energy released when simply burning the food in a furnace, because even though the process is wholly different, the begin and end products are the same. This is barely nutrition, this is just basic thermodynamics. Again, because energy is a state function, no assumptions need to be made about the efficiency of any of the intermediate processes or about how the muscles/mitochondria/liver/kidneys/... work, energy conservation keeps us from having to mess with that. The reason this analysis is so useful is because we're an endothermic species. The core of all of our bodies are at pretty much the same temperature. And as anyone who's had to pay a heating bill knows, heat isn't cheap. In fact, the bulk of our food energy is expended on keeping us warm. This is why there are no such things as slow or fast metabolism. If your metabolism were too slow to burn your resting energy expenditure in 24 hours, you'd die of undercooling. If your metabolism were significantly faster than normal, you'd die of overheating (or at least you'd feel significantly warm to the touch, be constantly sweating/flushed). In fact, a person's resting metabolic rate can be accurately predicted from their body composition [0], and doesn't differ between age or gender, as would be expected. This puts a pretty high lower limit on one's energy expenditure, absolutely nobody can maintain their weight on, say, 600 calories per day. You simply can't keep a 70 kg sack of mostly water at the right temperature with that energy budget, not with how badly isolated we are. Even if it does seem oversimplified, it's no spherical cow. The energy balance is exact, because of basic physics and biochemistry: we have only one way of generating energy (oxidizing reduced carbon), only one way of storing energy for the long term (long chains of reduced carbon), no energy is lost (because heat generation is a 100% efficient process) and our digestion is very efficient (not feces, urine nor sweat contain significant amounts of carbohydrates, lipids, protein or any other high-energy compound). It's also useful because we have an unflexible lower limit to the amount of energy we expend in a day because of the way our bodies work. The wiggle-room on the previous assumptions only serves to make calories-in smaller (e.g. malabsorption) or calories-out larger (e.g. exercise), and thus would only make it easier to lose weight. I won't deny the microbiome is important. There is a probably a correlation between gut biome and obesity. But that can only because it influences things like satiety or mood, because none of those bacteria seem to change the eventual energy equation, nor do they change how much heat you need to produce to keep warm or energy expended when lifting a weight. They're relevant because willpower is a finite resource, but they don't change the fact that any diet will in some sense need to consist of eating less calories than you burn in a day 0: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3139779/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3139779/

WorldMaker 10y ago
« When considering just the energy balance » Which is a simplifying assumption that I'm having trouble with here. "Energy balance" does not directly correlate with mass. Yes, there are a lot of indirect relationships and I appreciate you expanding upon them, but in the supposed logic chain of balance energy and thus balance mass, I think there are too many simplifying assumptions that black box the variety and depth of biochemical processes without factoring for them or building an error model for them. There is nothing wrong with using a black box model for a first order estimation/approximation, knowing your error bars and limitations and what next steps you would need to get more accurate data. I think there is something wrong with putting blinders on and pretending that your black box model is the entirety of the facts and can contain no error. You mention enthalpy, but roughly ignore the entirety of entropy in the equation; you are essentially handwaving it as an unimportant. I think it's lack in the model is telling. (There are multiple reasons the SI switched from calories to Joules as the measure of energy, and phlogiston-influenced thermodynamic baggage is part of that.) « we have only one way of generating energy (oxidizing reduced carbon) » We absolutely have anaerobic energy processes at work in our bodies every day. Muscle tissues are an example. The long tail variety of microorganism in our microbiome certainly includes plenty of other examples, our old friend yeast being a prime example. I could pick apart the other incorrect assumptions from your oversimplifying model, but this one alone is telling enough. « They're relevant because willpower is a finite resource » Here's the real problem: there is no direct correlation between mass and "willpower". Bringing up willpower here is slippery slope attempt to make a connection between weight and morality that is unjust at best. That is where the "calories in, calories out" rhetoric absolutely swerves to become more religious revival (the Protestant work ethic applied to food and exercise) than anything resembling science. Teach the controversy.
- kmm 10y ago
  Our mass directly correlates with the energy balance because we can't make energy from nothing, we get it from stores of high energy compounds containing reduced carbon (Preferably fat, but strict diets can lead to loss of muscle mass as well). I've already explained the key assumptions that make the black box model perform so well, and I don't see a massive problem with any of them. Definitely not any that make weight loss impossible or an insurmountable task (i.e. requiring to eat minuscule amounts) Entropy is irrelevant and I can't explain why if I don't know why you think it is (possible retorts: we don't use heat engines to perform work, the bulk of our food energy goes to heat and producing heat is always 100% efficient, the reaction rates are not dependent on Gibbs energy because of enzymes etc..). I never said my black box model is completely accurate. It would be if we had all the parameters, but we don't. The calories-in part is 99% accurate and it helps that it's an upper limit. The calories-out part is harder to predict, but one can get close enough when considering just the basal metabolic rate necessary for survival, that even mechanically ventilated people need to live. > We absolutely have anaerobic energy processes at work in our bodies every day. Muscle tissues are an example. The long tail variety of microorganism in our microbiome certainly includes plenty of other examples, our old friend yeast being a prime example. First of all, I explicitly mentioned exercise as one of caveats. But unless you're a top athlete, it's a pretty small part of the energy balance anyways, and on my usual day my muscles are rarely starved of oxygen. And it still doesn't matter because it doesn't change the energy equation! The rest product of anaerobic fermentation in our body is a relatively high energy compound called lactate. We don't expel most of it, so it's not part of calories-out. It gets converted back into glucose and stays part of our mass. Same with the anaerobic microbiome. They don't make our feces more nutritious and they don't perform useful work (in the physics sense), so either they make heat or they expel high energy compounds that we then absorb and metabolize as part of calories-in. I think it's unfair for you to accuse me of having blinders on. I don't pretend to know everything about the biochemistry of the human body. But I do know the constraints physics puts on it. I'm lucky that our body just so happens to work in a way that I can quite confidently state these things because of a few key assumptions that allow me to abstract over it using basic physics. I'm more than willing to revise my ideas, but you or someone else will first have to give strong facts which is not what I've seen here. One would also have to explain why caloric restriction works perfectly fine in a controlled environment (as many, many articles prove). Or simply explain how with a reduced caloric intake, one could supposedly stay alive without losing mass. Heck, as much as I rue anecdotal evidence, you can try it yourself. > Here's the real problem: there is no direct correlation between mass and "willpower". Bringing up willpower here is slippery slope attempt to make a connection between weight and morality that is unjust at best. That is where the "calories in, calories out" rhetoric absolutely swerves to become more religious revival (the Protestant work ethic applied to food and exercise) than anything resembling science. Teach the controversy. Good thing I'm Catholic then, and not even American. Diet is nothing but willpower. I won't pretend it's easy. Life is already hard and dieting takes a long time of fighting a basic instinct. But even if you don't believe in "calories-in, calories-out" (which I still don't think is justified), everyone believes in conservation of mass. If you eat less, you'll lose weight: http://blog.ifac-control.org/2016/12/05/closed-loop-weight-control-the-power-of-feedback/ http://blog.ifac-control.org/2016/12/05/closed-loop-weight-c... I don't make any moral judgments about this, as I rarely do: I could never pretend to know another person's struggle. I don't think the recent obesity epidemic is a sudden widespread moral failure, but rather an change in environment that had an unexpected effect. But I also don't like ungrounded excuses, nor how quite a few of the comments on this page don't provide any evidence for quite extraordinary claims.

by kmm 10y ago

WorldMaker 10y ago

« When considering just the energy balance » Which is a simplifying assumption that I'm having trouble with here. "Energy balance" does not directly correlate with mass. Yes, there are a lot of indirect relationships and I appreciate you expanding upon them, but in the supposed logic chain of balance energy and thus balance mass, I think there are too many simplifying assumptions that black box the variety and depth of biochemical processes without factoring for them or building an error model for them. There is nothing wrong with using a black box model for a first order estimation/approximation, knowing your error bars and limitations and what next steps you would need to get more accurate data. I think there is something wrong with putting blinders on and pretending that your black box model is the entirety of the facts and can contain no error. You mention enthalpy, but roughly ignore the entirety of entropy in the equation; you are essentially handwaving it as an unimportant. I think it's lack in the model is telling. (There are multiple reasons the SI switched from calories to Joules as the measure of energy, and phlogiston-influenced thermodynamic baggage is part of that.) « we have only one way of generating energy (oxidizing reduced carbon) » We absolutely have anaerobic energy processes at work in our bodies every day. Muscle tissues are an example. The long tail variety of microorganism in our microbiome certainly includes plenty of other examples, our old friend yeast being a prime example. I could pick apart the other incorrect assumptions from your oversimplifying model, but this one alone is telling enough. « They're relevant because willpower is a finite resource » Here's the real problem: there is no direct correlation between mass and "willpower". Bringing up willpower here is slippery slope attempt to make a connection between weight and morality that is unjust at best. That is where the "calories in, calories out" rhetoric absolutely swerves to become more religious revival (the Protestant work ethic applied to food and exercise) than anything resembling science. Teach the controversy.

kmm 10y ago
Our mass directly correlates with the energy balance because we can't make energy from nothing, we get it from stores of high energy compounds containing reduced carbon (Preferably fat, but strict diets can lead to loss of muscle mass as well). I've already explained the key assumptions that make the black box model perform so well, and I don't see a massive problem with any of them. Definitely not any that make weight loss impossible or an insurmountable task (i.e. requiring to eat minuscule amounts) Entropy is irrelevant and I can't explain why if I don't know why you think it is (possible retorts: we don't use heat engines to perform work, the bulk of our food energy goes to heat and producing heat is always 100% efficient, the reaction rates are not dependent on Gibbs energy because of enzymes etc..). I never said my black box model is completely accurate. It would be if we had all the parameters, but we don't. The calories-in part is 99% accurate and it helps that it's an upper limit. The calories-out part is harder to predict, but one can get close enough when considering just the basal metabolic rate necessary for survival, that even mechanically ventilated people need to live. > We absolutely have anaerobic energy processes at work in our bodies every day. Muscle tissues are an example. The long tail variety of microorganism in our microbiome certainly includes plenty of other examples, our old friend yeast being a prime example. First of all, I explicitly mentioned exercise as one of caveats. But unless you're a top athlete, it's a pretty small part of the energy balance anyways, and on my usual day my muscles are rarely starved of oxygen. And it still doesn't matter because it doesn't change the energy equation! The rest product of anaerobic fermentation in our body is a relatively high energy compound called lactate. We don't expel most of it, so it's not part of calories-out. It gets converted back into glucose and stays part of our mass. Same with the anaerobic microbiome. They don't make our feces more nutritious and they don't perform useful work (in the physics sense), so either they make heat or they expel high energy compounds that we then absorb and metabolize as part of calories-in. I think it's unfair for you to accuse me of having blinders on. I don't pretend to know everything about the biochemistry of the human body. But I do know the constraints physics puts on it. I'm lucky that our body just so happens to work in a way that I can quite confidently state these things because of a few key assumptions that allow me to abstract over it using basic physics. I'm more than willing to revise my ideas, but you or someone else will first have to give strong facts which is not what I've seen here. One would also have to explain why caloric restriction works perfectly fine in a controlled environment (as many, many articles prove). Or simply explain how with a reduced caloric intake, one could supposedly stay alive without losing mass. Heck, as much as I rue anecdotal evidence, you can try it yourself. > Here's the real problem: there is no direct correlation between mass and "willpower". Bringing up willpower here is slippery slope attempt to make a connection between weight and morality that is unjust at best. That is where the "calories in, calories out" rhetoric absolutely swerves to become more religious revival (the Protestant work ethic applied to food and exercise) than anything resembling science. Teach the controversy. Good thing I'm Catholic then, and not even American. Diet is nothing but willpower. I won't pretend it's easy. Life is already hard and dieting takes a long time of fighting a basic instinct. But even if you don't believe in "calories-in, calories-out" (which I still don't think is justified), everyone believes in conservation of mass. If you eat less, you'll lose weight: http://blog.ifac-control.org/2016/12/05/closed-loop-weight-control-the-power-of-feedback/ http://blog.ifac-control.org/2016/12/05/closed-loop-weight-c... I don't make any moral judgments about this, as I rarely do: I could never pretend to know another person's struggle. I don't think the recent obesity epidemic is a sudden widespread moral failure, but rather an change in environment that had an unexpected effect. But I also don't like ungrounded excuses, nor how quite a few of the comments on this page don't provide any evidence for quite extraordinary claims.