2001 Science in Society Journalism Awards

Magazine

Gary Taubes

“The Soft Science of Dietary Fat”

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Part Five: The test of time

To the outside observer, the challenge in making sense of any such long-running scientific controversy is to establish whether the skeptics are simply on the wrong side of the new paradigm, or whether their skepticism is well founded. In other words, is the science at issue based on sound scientific thinking and unambiguous data, or is it what Sir Francis Bacon, for instance, would have called "wishful science," based on fancies, opinions, and the exclusion of contrary evidence? Bacon offered one viable suggestion for differentiating the two: the test of time. Good science is rooted in reality, so it grows and develops and the evidence gets increasingly more compelling, whereas wishful science flourishes most under its first authors before "going downhill."

Such is the case, for instance, with the proposition that dietary fat causes cancer, which was an integral part of dietary fat anxiety in the late 1970s. By 1982, the evidence supporting this idea was thought to be so undeniable that a landmark NAS report on nutrition and cancer equated those researchers who remained skeptical with "certain interested parties [who] formerly argued that the association between lung cancer and smoking was not causational." Fifteen years and hundreds of millions of research dollars later, a similarly massive expert report by the World Cancer Research Fund and the American Institute for Cancer Research could find neither "convincing" nor even "probable" reason to believe that dietary fat caused cancer.

The hypothesis that low-fat diets are the requisite route to weight loss has taken a similar downward path. This was the ultimate fallback position in all low-fat recommendations: Fat has nine calories per gram compared to four calories for carbohydrates and protein, and so cutting fat from the diet surely would cut pounds. "This is held almost to be a religious truth," says Harvard’s Willett. Considerable data, however, now suggest otherwise. The results of well-controlled clinical trials are consistent: People on low-fat diets initially lose a couple of kilograms, as they would on any diet, and then the weight tends to return. After 1 to 2 years, little has been achieved. Consider, for instance, the 50,000 women enrolled in the ongoing $100 million Women’s Health Initiative (WHI). Half of these women have been extensively counseled to consume only 20% of their calories from fat. After 3 years on this near-draconian regime, say WHI sources, the women had lost, on average, a kilogram each.

The link between dietary fat and heart disease is more complicated, because the hypothesis has diverged into two distinct propositions: first, that lowering cholesterol prevents heart disease; second, that eating less fat not only lowers cholesterol and prevents heart disease but prolongs life. Since 1984, the evidence that cholesterol-lowering drugs are beneficial — proposition number one — has indeed blossomed, at least for those at high risk of heart attack. These drugs reduce serum cholesterol levels dramatically, and they prevent heart attacks, perhaps by other means as well. Their market has now reached $4 billion a year in the United States alone, and every new trial seems to confirm their benefits.

The evidence supporting the second proposition, that eating less fat makes for a healthier and longer life, however, has remained stubbornly ambiguous. If anything, it has only become less compelling over time. Indeed, since Ancel Keys started advocating low-fat diets almost 50 years ago, the science of fat and cholesterol has evolved from a simple story into a very complicated one. The catch has been that few involved in this business were prepared to deal with a complicated story. Researchers initially preferred to believe it was simple — that a single unwholesome nutrient, in effect, could be isolated from the diverse richness of human diets; public health administrators required a simple story to give to Congress and the public; and the press needed a simple story — at least on any particular day — to give to editors and readers in 30 column inches. But as contrarian data continued to accumulate, the complications became increasingly more difficult to ignore or exclude, and the press began waffling or adding caveats. The scientists then got the blame for not sticking to the original simple story, which had, regrettably, never existed.

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Last revised: August 27, 2006

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