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> measuring calories out is extremely difficult unless you're willing to live in a sealed room that monitors your exhaled CO2 24/7 Is even that sufficient? Li

> measuring calories out is extremely difficult unless you're willing to live in a sealed room that monitors your exhaled CO2 24/7 Is even that sufficient? Like, would you be able to tell the difference between "oxidation done by the body to generate energy for human cells" and "oxidation done by bacteria that feast on calories your human cells didn't get"? Maybe you could tell by the mixture of other gases, but I suspect CO2 itself wouldn't suffice.

hattmall 5y ago
>"oxidation done by bacteria that feast on calories your human cells didn't get"? That would still be part of calories in.
_9omd 5y ago
Yeah, that's a very good point. This is kinda getting off into the weeds from the original point, but interesting weeds nonetheless :). This study[0] says that measuring CO2 is not enough, and that indirect calorimetry is the gold standard for measuring energy expenditure (EE). "Calculated EE based on CO2 measurement was not sufficiently accurate to consider the results as an alternative to measured EE by indirect calorimetry. Therefore, EE measured by indirect calorimetry remains as the gold standard to guide nutrition therapy." Google says "Indirect calorimetry is the method by which measurements of respiratory gas exchange (oxygen consumption, V O 2 and carbon dioxide production, V CO 2 ) are used to estimate the type and amount of substrate oxidized and the amount of energy produced by biological oxidation." So getting back to your point, if bacteria are feasting on part of the calories and producing CO2, it seems that it would throw off the results even using indirect calorimetry. At that point though are we kinda arguing semantics? While our microbiome isn't composed of human cells, you can still argue it's a part of our functioning organism. It seems it would be nearly impossible to measure human digested calories vs bacteria digested calories, so maybe the results are close enough. Also, many beneficial bacteria release calories that we can consume, like butyric acid, which further complicates things. [0] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5251283/ https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5251283/
- Dylan16807 5y ago
  > At that point though are we kinda arguing semantics? While our microbiome isn't composed of human cells, you can still argue it's a part of our functioning organism. It's not semantics, because when more calories are used up by bacteria they only sustain the amount of bacteria inside you, which then die and leave your body on a relatively quick timescale. It's like if your fat cells could only store fat for a month before it gets discarded. So it's important to know how much is each, if they can both vary.
- waterhouse 5y ago
  Let's consider a specific example: Lactose intolerance. The Wiki page for it is pretty good. So, despite the name, lactose intolerance refers to lacking the enzyme lactase, which is used to break down lactose. If you have lactase, then your human cells can use the calories from lactose; if you don't, then the bacteria get the lactose. Wiki says "Symptoms may include abdominal pain, bloating, diarrhea, gas, and nausea", which sounds like the bacteria do indeed eat it; if the bacteria couldn't extract calories from it either, then I assume it would just pass through and there would be no symptoms. Thus, if Bob and Joe eat the exact same diet that has some milk products, and Bob is lactose intolerant while Joe isn't, then Bob's cells get fewer calories from that diet than Joe's. If Bob and Joe's bodies are otherwise identical and follow identical exercise routines, then I would assume that, like, if the diet is exactly enough to maintain Joe's weight, then Bob would lose weight; and if it's exactly enough to maintain Bob's weight, then Joe would gain weight. (Right? For sake of illustration, we could imagine that most of the diet's calories are from milk, and assume Bob can tolerate the nausea.) Yet "calories in" (measured as food entering stomach) are identical, and "calories out" (measured as CO2) might also be identical. Lactose is a specific, well-understood example of some people absorbing nutrients much better than others. I think there are other examples, and I expect there's a lot of variation in absorption efficiency that's less known. When you hear about people who eat lots of food and remain thin, I suspect this is part of the explanation. And whether their bacteria get the calories instead, or whether it passes through untouched, might show up in CO2 measurements but I don't think it would be related to body fat accumulation. In a conservation-of-energy sense, "calories in" certainly gives you an upper bound on how many observed "calories out" you can produce without losing weight. But I don't think there's a lower bound on how inefficient someone's digestive system can be (except "zero"), or a practical upper bound on how much their cells might burn energy without us noticing (without close observation). I think, if you wanted a complete accounting of calories-out that would actually match the input, you'd need to add up (a) the heat a person puts out (via contact with air and surfaces, also infrared emissions), (b) the work they do in a physics sense (e.g. lifting heavy objects), and (c) the amount of un-burned calories in their stool (or any other excreted substances).

hattmall 5y ago

>"oxidation done by bacteria that feast on calories your human cells didn't get"? That would still be part of calories in.

_9omd 5y ago

Yeah, that's a very good point. This is kinda getting off into the weeds from the original point, but interesting weeds nonetheless :). This study[0] says that measuring CO2 is not enough, and that indirect calorimetry is the gold standard for measuring energy expenditure (EE). "Calculated EE based on CO2 measurement was not sufficiently accurate to consider the results as an alternative to measured EE by indirect calorimetry. Therefore, EE measured by indirect calorimetry remains as the gold standard to guide nutrition therapy." Google says "Indirect calorimetry is the method by which measurements of respiratory gas exchange (oxygen consumption, V O 2 and carbon dioxide production, V CO 2 ) are used to estimate the type and amount of substrate oxidized and the amount of energy produced by biological oxidation." So getting back to your point, if bacteria are feasting on part of the calories and producing CO2, it seems that it would throw off the results even using indirect calorimetry. At that point though are we kinda arguing semantics? While our microbiome isn't composed of human cells, you can still argue it's a part of our functioning organism. It seems it would be nearly impossible to measure human digested calories vs bacteria digested calories, so maybe the results are close enough. Also, many beneficial bacteria release calories that we can consume, like butyric acid, which further complicates things. [0] https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5251283/ https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5251283/

Dylan16807 5y ago
> At that point though are we kinda arguing semantics? While our microbiome isn't composed of human cells, you can still argue it's a part of our functioning organism. It's not semantics, because when more calories are used up by bacteria they only sustain the amount of bacteria inside you, which then die and leave your body on a relatively quick timescale. It's like if your fat cells could only store fat for a month before it gets discarded. So it's important to know how much is each, if they can both vary.
waterhouse 5y ago
Let's consider a specific example: Lactose intolerance. The Wiki page for it is pretty good. So, despite the name, lactose intolerance refers to lacking the enzyme lactase, which is used to break down lactose. If you have lactase, then your human cells can use the calories from lactose; if you don't, then the bacteria get the lactose. Wiki says "Symptoms may include abdominal pain, bloating, diarrhea, gas, and nausea", which sounds like the bacteria do indeed eat it; if the bacteria couldn't extract calories from it either, then I assume it would just pass through and there would be no symptoms. Thus, if Bob and Joe eat the exact same diet that has some milk products, and Bob is lactose intolerant while Joe isn't, then Bob's cells get fewer calories from that diet than Joe's. If Bob and Joe's bodies are otherwise identical and follow identical exercise routines, then I would assume that, like, if the diet is exactly enough to maintain Joe's weight, then Bob would lose weight; and if it's exactly enough to maintain Bob's weight, then Joe would gain weight. (Right? For sake of illustration, we could imagine that most of the diet's calories are from milk, and assume Bob can tolerate the nausea.) Yet "calories in" (measured as food entering stomach) are identical, and "calories out" (measured as CO2) might also be identical. Lactose is a specific, well-understood example of some people absorbing nutrients much better than others. I think there are other examples, and I expect there's a lot of variation in absorption efficiency that's less known. When you hear about people who eat lots of food and remain thin, I suspect this is part of the explanation. And whether their bacteria get the calories instead, or whether it passes through untouched, might show up in CO2 measurements but I don't think it would be related to body fat accumulation. In a conservation-of-energy sense, "calories in" certainly gives you an upper bound on how many observed "calories out" you can produce without losing weight. But I don't think there's a lower bound on how inefficient someone's digestive system can be (except "zero"), or a practical upper bound on how much their cells might burn energy without us noticing (without close observation). I think, if you wanted a complete accounting of calories-out that would actually match the input, you'd need to add up (a) the heat a person puts out (via contact with air and surfaces, also infrared emissions), (b) the work they do in a physics sense (e.g. lifting heavy objects), and (c) the amount of un-burned calories in their stool (or any other excreted substances).