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Desrtopa comments on How I Lost 100 Pounds Using TDT - Less Wrong
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I am not sure I am convinced by this argument, for the following reasons:
If you think of calorie content / thermodynamics as an upper bound on how much energy can be extracted from the food, you have to make an argument for what happens to the unused energy. Even if you are in a biochemical state where not all the energy is used, there is still energy floating around in your body in the form of carbohydrates, fat and protein. I can think of three possible mechanisms for what happens to this extra energy, and I am not convinced by any of them:
(1) Calories are excreted unused in their original form. However, I don't think this happens to a meaningful extent
(2) If there is excess fat, nutrients are broken down to molecular constituents in a less efficient mechanism of cellular metabolism, ie, producing less ATP. This is a little more plausible than 1, but I think it would be evolutionary maladaptive to reduce the fuel efficiency of your engine unless it was absolutely necessary. Note that there are cases when the body does reduce the fuel efficiency (such as anaerobic metabolism), but I can't see how this applies here
(3) (Added): If there is excess fat, the body begins to run processes that are not strictly necessary, thus using more fuel. However, I am not sure what these processes would be, or why they would be triggered by fat and not carbohydrates.
I find it plausible that increasing fat intake will help you lose weight due to regulatory pathways such as insulin, but I think this pathway operates almost exclusively through changes in appetite. I fail to see any arguments why we cannot use thermodynamics (calorie input/output) as a very good approximation of predicted weight change.
EDIT: This comment is being downvoted. I am happy to delete it if it doesn't add to the discussion, but it would help me immensely if someone could explain why my reasoning is wrong...
EDIT2: I am not sure if I misunderstand the karma system, but I don't think you are supposed to downvote someone for disagreeing with their conclusions. It is possible that I am wrong in my conclusions, but I don't think this in itself is reason for downvoting.
If you disagree with my arguments, you can dissect them in the comments. Reasonable arguments with incorrect conclusions are still valuable in a discussion, and if you show why they are wrong, you will not only help me update my priors, but also help reveal a flaw in how non-trolls come to their beliefs. Hiding the comment prevents this. I don't see any reason for downvoting, and I think the downvoters need to ask themselves if they are downvoting due to mood affiliation / cognitive bias.
I think this can actually happen to a very great extent depending on how much the person normally eats and burns, and how quickly they consume it, and is the main mechanism by which e.g. competitive eaters generally avoid becoming obese.
By which mechanism do these nutrients get excreted? Urine? Bile? Non-absorption?
My impression is that carbohydrates in urine is something that we only see to a significant extent when blood glucose concentration is at diabetic levels. Protein and fat in urine occurs, but it doesn't seem to me that this happens to an extent where it can make a difference to the total energy picture
I don't think excreting them through bile would work, the nutrients would just be reabsorbed further down the gastrointestinal tract.
It is possible that at very high intake levels, there is significant non-absorption of fat. Maybe this happens in competitive eaters, but I am not convinced it can explain much at fat intake levels seen in ordinary people..
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1793018/
(Bam.) So, under normal conditions you're pretty efficient (~4% of your calories just get pooped back out), meaning that something like metabolic rate just swamps poop-energy-content as an interpersonal variable.
This article says that there is some non-absorption of fat in healthy people, and much greater non-absorption in people with cystic fibrosis.
If you want to convince me that I should consider this when I choose the fat/carbohydrate/protein content of my diet, you would have to make an argument that the percentage of fat that is not absorbed is a function of my diet, ie, causally related to what I choose to eat.
I'm not saying this is not theoretically possible, but my intuition tells me that the variation in absorbtion that is caused by diet, is unlikely to have a major impact in the final analysis
So, Tim Ferris has done a couple of demonstrations where he ate about 20,000 calories in the course of 24 hours. The vast majority of that is not absorbed.
You may have had in mind the limited claim that macronutrient ratio has a small effect on the percentage of calories absorbed, which seems reasonable for normal macronutrient ratios, but quantity seems important, as well as more detailed chemical composition. For example, I don't produce enough lactase to digest normal American quantities of milk consumption without chemical assistance, and so if I continued to drink a glass of milk each day, the amount of calories that made it into my bloodstream would be predictably lower than the amount of calories put into my mouth.
So while the CI calculation can be complex, it seems obvious to me that the amount of calories you put in your mouth is a good upper bound. (I don't think this is seriously contested by anyone, but it's worthwhile to establish that it's not seriously contested.) The system dynamics may mean that in some cases a higher total number of calories in leads to a lower maintenance weight, and so just lowering intake is not always the right solution.