Gary Taubes, a writer for Science magazine, is the author of the soon-to-be-released book Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Weight Control and Disease (Knopf September 25, 2007). He provides a don’t miss preview of his book in this past Sunday’s New York Times:

Many explanations have been offered to make sense of the here-today-gone-tomorrow nature of medical wisdom ó what we are advised with confidence one year is reversed the next ó but the simplest one is that it is the natural rhythm of science. An observation leads to a hypothesis. The hypothesis (last yearís advice) is tested, and it fails this yearís test, which is always the most likely outcome in any scientific endeavor. There are, after all, an infinite number of wrong hypotheses for every right one, and so the odds are always against any particular hypothesis being true, no matter how obvious or vitally important it might seem. [. . .]
The dangerous game being played here, as David Sackett, a retired Oxford University epidemiologist, has observed, is in the presumption of preventive medicine. The goal of the endeavor is to tell those of us who are otherwise in fine health how to remain healthy longer. But this advice comes with the expectation that any prescription given ó whether diet or drug or a change in lifestyle ó will indeed prevent disease rather than be the agent of our disability or untimely death. With that presumption, how unambiguous does the evidence have to be before any advice is offered? [. . .]
Richard Peto, professor of medical statistics and epidemiology at Oxford University, phrases the nature of the conflict this way: ìEpidemiology is so beautiful and provides such an important perspective on human life and death, but an incredible amount of rubbish is published,î by which he means the results of observational studies that appear daily in the news media and often become the basis of public-health recommendations about what we should or should not do to promote our continued good health. [. . .]
All of this suggests that the best advice is to keep in mind the law of unintended consequences. The reason clinicians test drugs with randomized trials is to establish whether the hoped-for benefits are real and, if so, whether there are unforeseen side effects that may outweigh the benefits. If the implication of an epidemiologistís study is that some drug or diet will bring us improved prosperity and health, then wonder about the unforeseen consequences. In these cases, itís never a bad idea to remain skeptical until somebody spends the time and the money to do a randomized trial and, contrary to much of the history of the endeavor to date, fails to refute it.

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