Friday night topic: Low-fat oops! Whither science?

A major study has shown that low-fat diets don't appear to reduce risk of cancer or heart disease, very much contrary to accepted wisdom. This no backwoods scientific endeavor, either; it is the largest study ever on this topic, unusual for its size and scope, as the New York Times points out:
The $415 million federal study involved nearly 49,000 women ages 50 to 79 who were followed for eight years. In the end, those assigned to a low-fat diet had the same rates of breast cancer, colon cancer, heart attacks and strokes as those who ate whatever they pleased, researchers are reporting today.

"These studies are revolutionary," said Dr. Jules Hirsch, physician in chief emeritus at Rockefeller University in New York City, who has spent a lifetime studying the effects of diets on weight and health. "They should put a stop to this era of thinking that we have all the information we need to change the whole national diet and make everybody healthy."

The study, published in today's issue of The Journal of the American Medical Association, was not just an ordinary study, said Dr. Michael Thun, who directs epidemiological research for the American Cancer Society. It was so large and so expensive, Dr. Thun said, that it was "the Rolls-Royce of studies." As such, he added, it is likely to be the final word.

First it was salt, and now fat, that was almost universally proclaimed a health risk before studies showed otherwise. A lot of people have been eating lousy-tasting food for the sake of iffy science, it would seem. How could this happen? One statistician involved had this explanation:
But Dr. Freedman, the Berkeley statistician, said the overall lesson was clear.

"We, in the scientific community, often give strong advice based on flimsy evidence," he said. "That's why we have to do experiments."

That seems to be the heart of the problem. Yet you can see the spinning happening in the quotations from "experts" in the NY Times story and others, with some folks advocating the so-called Mediterranean diet while others tried to dismiss out of hand the biggest and best study to date on this issue. The fight is on to establish the tone of the new consensus or protect the current one.

For me, this raises the question: How much do we really know about these matters, and what is the value of the current consensus on such things? Do the politics of such hot-button health issues cloud our ability to assemble the evidence into meaningful advice without overstepping? Does the scientific and medical consensus really progress over time, or does it just change?

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