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brazil84 comments on What false beliefs have you held and why were you wrong? - Less Wrong Discussion
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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.
Do you have a source for the claim that fat people don't generally have slow metabolisms?
I assume you mean some kind of formal reference as opposed to common sense arguments or general observations. If so, are you seriously skeptical of the claim? If the answer is "yes," then I will try to dig something up.
I am sceptical of that claim, too.
I don't expect all fat people to have slow metabolisms, but I expect slow metabolism to be more prevalent among fat people as compared to thin people.
For example, there is a correlation between people's metabolism slowing down as they age and people gaining weight as they age (we're talking about the progression from, say, the 20s into the middle age, not old age). I am not ready to pronounce it a causal relationship, but the correlation is there.
That's not quite the claim I was addressing - the claim is that generally speaking, obesity is the result of having a slow metabolism. But anyway, I was able to dig up some evidence:
First, a video which is obviously not a scientific study but still pretty compelling:
http://www.youtube.com/watch?v=KA9AdlhB18o
In this video, a fat girl who believes she is fat because of a "slow metabolism," is tested. It turns out that she has a perfectly normal metabolism but eats a lot more than she realizes.
Here is a similar video:
http://www.youtube.com/watch?v=WGLwzbvx4S4
Scientific research would seem to indicate that this is pretty typical. i.e. people are fat not because of their "slow metabolism" but because they eat a lot more than they realize:
http://www.nejm.org/doi/pdf/10.1056/NEJM199212313272701
Here is a study which looked at a group of people and determined that the fatter subjects had higher metabolic rates than the thinner ones:
http://ajcn.nutrition.org/content/35/3/566.short
If you search, there are a lot of studies like this out there. AFAIK, most (but not all) scientific studies have found that obese people have higher metabolisms than thin people.
My guess is that this is largely because obese people regularly overeat and so their metabolisms rev up a bit in a futile effort to handle the onslaught of calories. There may be a few studies out there which indicate that obese people have slower metabolisms, but I suspect the differences are pretty minor when you look at the real problem: Fat people eat a lot more than they realize, which is something that every study looking at this issue has concluded.
That looks to be a strawman. I am sure you can find on TV, but I am unaware of anyone reasonably serious holding this view.
:shrug: That's what I believed. Anyway, your response is a bit of a True Scotsman argument. If I find 100 people who expressed similar beliefs, you can simply dismiss them as not being "reasonably serious."
Let's do this: How do I know if someone is "reasonably serious" or not?
In the same way saying that no one serious believes in perpetual motion machines is also a True Scotsman argument.
Has adequate knowledge of human physiology and is not trolling :-P
Yes, I would say that it suffers from basically the same same problem. Do you agree that there are people out there who believe, in good faith, that perpetual motion machines are possible? Do you agree that there are people who invest a lot of personal time and energy into constructing perpetual motion machines?
Okay, and if someone asserts or implies that generally speaking obesity is caused by low metabolism, how do I know if they have adequate knowledge of human physiology and are not trolling?
And let's look at the girls in the two videos they linked. Although they did not make general statements about the causes of obesity, they did seem to believe at the beginning that their obesity was caused by slow metabolism, agreed? Would you agree that those two girls were not trolling? And in your opinion, did they have adequate knowledge of human physiology? If not, how do you know it?
In short, are those two girls "reasonably serious"?
Here I mean "serious" in the external-observer sense -- to denote people whom others consider serious = worthy of attention and time. I do NOT mean "serious" in the internal perception sense (as in e.g. "I'm not joking, I'm serious").
This is interesting enough that I'd like to see some more explanation, too.
See my reply to Lumifer above.
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.