Wednesday, February 8, 2006


For decades, nutritionists, doctors, and others have recommended low-fat diets for their health benefits. In recent decades, this community has attributed reduced rates of cancer (especially colon cancer and breast cancer), heart attacks, and strokes to such a diet. Millions of people have tried, with varying success, to follow the (wildly variable and conflicting) guidelines propounded by these people in an effort to improve their health or simply to lose weight.


A just-published, $415M, eight-year federal study of 49,000 women concludes that a low-fat diet in fact does none of these things (at least, not with the study’s target audience of 50 to 79 year old women). Women on low-fat diets had cancer rates, heart attack rates, and stroke rates insignificantly different from those of women who ate whatever the heck they wanted to.


And it gets worser: the women on the low-fat diets didn’t even succeed in losing weight.

Oops and double-oops.

Lest you think this study was some light-weight, flaky, fly-by-night sort of thing, consider this:

From the New York Times:

"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.

"We usually have only one shot at a very large-scale trial on a particular issue,” he said.


The way that this study turns preceding consensus belief on its head is a great example of the value of the scientific process. Even the combined education, experience, and intuition of a large group of well-informed people can turn out to be wrong — and has, on countless past occasions. We often mock the ancients for their belief that the universe revolved around the Earth — the the fact is that their beliefs were the consensus of the best-educated, best-informed, most-respected people of their time. We’re no different, and their are other recent medical beliefs to use as illustrations. For instance, just a couple of decades ago, the consensus amongst scientists and medical professionals was the stomach ulcers were caused by stress and excess acid. Oops. It turns out that they’re caused by a bacterium, and they are easily treated. Decades of well-informed consensus turned out to be wrong. Looks like they’re wrong again.

One difference with this particular affair, though, is that there is a multi-billion dollar industry with a vested interest in the belief that low-fat diets are healthy. This industry, it’s easy to predict, will do everything they possibly can to impeach this study. The battle will be interesting to watch…

I’ll leave you with the “money quote” from the NYT article (it’s also how they concluded):

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."


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