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dougclow comments on What false beliefs have you held and why were you wrong? - Less Wrong
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I used to think that overweight was caused by slow metabolism, i.e. that generally speaking fat people are people who have slow metabolisms and thin people are people who have fast metabolisms.
I believed this because (1) it is the conventional wisdom; (2) it is consistent with the observation that some people seem to be thin even though they stuff their faces; and (3) it makes sense from a thermodynamic perspective that someone with a slow metabolism would be prone to putting on weight and someone with a fast metabolism would be prone to staying thin.
Putting aside the fact that this belief was wrong, there does seem to be a certain degree of irrationality about it given the observation that people don't vary all that much in terms of body temperature. Therefore they must not vary all that much in terms of metabolism.
I don't think that follows, or at least not without a lot of other explanation, even if you grant that temperature doesn't vary in any significant way between people (which I'm not sure I do). The body has multiple mechanisms for maintaining temperature, of which metabolic rate is only one. It seems entirely plausible to me that people run their metabolisms at different rates and adjust their peripheral vasodilation and sweating rate to balance it all out near 37 C/98 F. Core temperature might vary between people by only a few degrees, but surface temperature varies much more widely.
That's an interesting point. Would you agree that if a person has a higher metabolism, one would expect that under your theory, their skin temperature would be expected to be higher?
For a given body-shape, they should. For a given metabolism people with lower surface to volume ratio (ie round people) should have higher skin temperature.
And spherical cows in vacuum should have the highest skin temperature of them all!
I would have to agree with this. I wonder how much of an impact body shape has.
That, and/or increased sweating, and/or larger temperature gain between inspired and expired air, or wearing fewer/thinner clothes. There's lots of ways to dump heat.
I would definitely expect someone with a faster metabolism to put out more total net heat, which is measurable with difficulty, and also consume oxygen faster (and produce carbon dioxide faster) which is measurable with some difficulty, but a lot less.
Yes, but that would require much more involved procedures than just taking peoples' temperature. So I will concede that my argument about variation in temperature, which is sort of a back-of-the-envelope way of getting at the problem, is weaker than I had thought.