I've been skeptical about the link between dietary fat, and weight and poor health for a long time (at least since I first read Barry Sears' analyses, over a decade ago). John Tierney (who has fortunately escaped from behind the Times Select prison) writes that the "science" behind the linkage is bogus, and that our fat aversion is probably one of the leading causes of obesity, since we switched to carbohydrates, which are much worse for us. But the reason that the bogus theory was promoted and accepted for so long is an interesting story of scientific sociology:

It may seem bizarre that a surgeon general could go so wrong. After all, wasn’t it his job to express the scientific consensus? But that was the problem. Dr. Koop was expressing the consensus. He, like the architects of the federal “food pyramid” telling Americans what to eat, went wrong by listening to everyone else. He was caught in what social scientists call a cascade.

We like to think that people improve their judgment by putting their minds together, and sometimes they do. The studio audience at “Who Wants to Be a Millionaire” usually votes for the right answer. But suppose, instead of the audience members voting silently in unison, they voted out loud one after another. And suppose the first person gets it wrong.

If the second person isn’t sure of the answer, he’s liable to go along with the first person’s guess. By then, even if the third person suspects another answer is right, she’s more liable to go along just because she assumes the first two together know more than she does. Thus begins an “informational cascade” as one person after another assumes that the rest can’t all be wrong.

Because of this effect, groups are surprisingly prone to reach mistaken conclusions even when most of the people started out knowing better, according to the economists Sushil Bikhchandani, David Hirshleifer and Ivo Welch. If, say, 60 percent of a group’s members have been given information pointing them to the right answer (while the rest have information pointing to the wrong answer), there is still about a one-in-three chance that the group will cascade to a mistaken consensus.

Cascades are especially common in medicine as doctors take their cues from others, leading them to overdiagnose some faddish ailments (called bandwagon diseases) and overprescribe certain treatments (like the tonsillectomies once popular for children). Unable to keep up with the volume of research, doctors look for guidance from an expert — or at least someone who sounds confident.

Hmmmmm.....does it sound like another current scientific "consensus"?

Of course, it doesn't mean that all theories have this problem. But it does mean that we are entitled to a little skepticism when we are told that there is a scientific consensus. Particularly when we are bullied into believing it, and treated like heretics in our skepticism, and there are some other potential agendas at play.

Of course, the good news for me (though it was too late for my parents) is that even if we don't know what is the best diet to prevent coronary disease, we are coming up with other, better solutions:

From a snippet of a patient’s skin, researchers have grown blood vessels in a laboratory and then implanted them to restore blood flow around the patient’s damaged arteries and veins.

As Instantman (from whom I got both these articles) says, bring it on.

[Wednesday morning update]

Jonathan Gewirtz has further thoughts.

Meanwhile, there still wasn’t good evidence to warrant recommending a low-fat diet for all Americans, as the National Academy of Sciences noted in a report shortly after the U.S.D.A. guidelines were issued. But the report’s authors were promptly excoriated on Capitol Hill and in the news media for denying a danger that had already been proclaimed by the American Heart Association, the McGovern committee and the U.S.D.A.

The scientists, despite their impressive credentials, were accused of bias because some of them had done research financed by the food industry. And so the informational cascade morphed into what the economist Timur Kuran calls a reputational cascade, in which it becomes a career risk for dissidents to question the popular wisdom.

With skeptical scientists ostracized, the public debate and research agenda became dominated by the fat-is-bad school.

What burns me up is that we'll see similar articles about AGW in ten or twenty years time with no apologies or recriminations. Maybe some dead pols and scientists will have their reputations tarnished but the media which plays such a big role in the whole 'informational cascade' will still be patting themselves on the back for the 'outstanding' work they do.

Maybe the best way to look at it is that, to first order, belief in any idea is the product of a cascade.

Take the idea that "Paris Hilton is a celebrity whose every action deserves national coverage." This is pretty obviously the product of an out-of-control cascade. Second-order influences involve things like "Is she hot?" (Any idea involving a woman has "Is she hot?" as at least a second-order influence.)

Science, properly so-called, has "Does it fit the data?" as the second-order influence. In cases like low-fat diets or AGW, that gets displaced from second-order by other questions, like "Does it promote my political agenda?"

This would explain an observation of mine, that we make tremendous progress on scientific questions that no one cares about. We know the gyromagnetic ratio of the electron to 11 significant figures. I don't suppose anyone gets emotional about any of those digits beyond the first four or so. But progress seems to be glacial on questions that people really care about, like weight loss or control of the economy. Precisely the cases where "Does it fit the data?" gets shoved out of second-order.

I eat meat, lots of it. I try to shoot for 200 grams of protein a day. Eggs, chicken, tuna, beef, and whey. It takes a lot of fuel to feed this impressive specimen of human biology. *eats a mouthful of beef jerky** mmmmmmmmMMMM!

I posted on this topic here.

The difference between global warming and the low-fat diet mania is the existence of quantitative, physics-based reasons for the former. Biological theories, on the other hand, are much less grounded in solid a priori information.

> The difference between global warming and the low-fat diet mania is the existence of quantitative, physics-based reasons for the former.

Not so fast. The physics of heat retention atomospheric CO2 do NOT tell us what, if anything, we should do.

Dr. Melik: This morning for breakfast he requested something called "wheat germ, organic honey and tiger's milk."
Dr. Aragon: [chuckling] Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.
Dr. Melik: You mean there was no deep fat? No steak or cream pies or... hot fudge?
Dr. Aragon: Those were thought to be unhealthy... precisely the opposite of what we now know to be true.
Dr. Melik: Incredible.

From "Sleeper". Woody Allen is a genius. :D

Not so fast. The physics of heat retention atomospheric CO2 do NOT tell us what, if anything, we should do.

Of course. But your are in effect changing the subject from 'scientific cascades' to 'policy cascades'.