2001 Science in Society Journalism Awards

Magazine

Gary Taubes

“The Soft Science of Dietary Fat”

NOTE: A .pdf version of “The Soft Science of Dietary Fat” is also available.

The reproduction of this article is intended for non-commercial, educational purposes only.

Part Two: Fear of fat

During the first half of the 20th century, nutritionists were more concerned about malnutrition than about the sins of dietary excess. After World War II, however, a coronary heart disease epidemic seemed to sweep the country (see sidebar on p. 2540). "Middle-aged men, seemingly healthy, were dropping dead," wrote biochemist Ancel Keys of the University of Minnesota, Twin Cities, who was among the first to suggest that dietary fats might be the cause. By 1952, Keys was arguing that Americans should reduce their fat intake to less than 30% of total calories, although he simultaneously recognized that "direct evidence on the effect of the diet on human arteriosclerosis is very little and likely to remain so for some time." In the famous and very controversial Seven Countries Study, for instance, Keys and his colleagues reported that the amount of fat consumed seemed to be the salient difference between populations such as those in Japan and Crete that had little heart disease and those, as in Finland, that were plagued by it. In 1961, the Framingham Heart Study linked cholesterol levels to heart disease, Keys made the cover of Time magazine, and the AHA, under his influence, began advocating low-fat diets as a palliative for men with high cholesterol levels. Keys had also become one of the first Americans to consciously adopt a heart-healthy diet: He and his wife, Time reported, "do not eat ’carving meat’ — steaks, chops, roasts — more than three times a week."

Nonetheless, by 1969 the state of the science could still be summarized by a single sentence from a report of the Diet-Heart Review Panel of the National Heart Institute (now the National Heart, Lung, and Blood Institute, or NHLBI): "It is not known whether dietary manipulation has any effect whatsoever on coronary heart disease." The chair of the panel was E. H. "Pete" Ahrens, whose laboratory at Rockefeller University in New York City did much of the seminal research on fat and cholesterol metabolism.

Whereas proponents of low-fat diets were concerned primarily about the effects of dietary fat on cholesterol levels and heart disease, Ahrens and his panel — 10 experts in clinical medicine, epidemiology, biostatistics, human nutrition, and metabolism — were equally concerned that eating less fat could have profound effects throughout the body, many of which could be harmful. The brain, for instance, is 70% fat, which chiefly serves to insulate neurons. Fat is also the primary component of cell membranes. Changing the proportion of saturated to unsaturated fats in the diet changes the fat composition in these membranes. This could conceivably change the membrane permeability, which controls the transport of everything from glucose, signaling proteins, and hormones to bacteria, viruses, and tumor-causing agents into and out of the cell. The relative saturation of fats in the diet could also influence cellular aging as well as the clotting ability of blood cells.

Whether the potential benefits of low-fat diets would exceed the potential risks could be settled by testing whether low-fat diets actually prolong life, but such a test would have to be enormous. The effect of diet on cholesterol levels is subtle for most individuals — especially those living in the real world rather than the metabolic wards of nutrition researchers — and the effect of cholesterol levels on heart disease is also subtle. As a result, tens of thousands of individuals would have to switch to low-fat diets and their subsequent health compared to that of equal numbers who continued eating fat to alleged excess. And all these people would have to be followed for years until enough deaths accumulated to provide statistically significant results. Ahrens and his colleagues were pessimistic about whether such a massive and expensive trial could ever be done. In 1971, an NIH task force estimated such a trial would cost $1 billion, considerably more than NIH was willing to spend. Instead, NIH administrators opted for a handful of smaller studies, two of which alone would cost $255 million. Perhaps more important, these studies would take a decade. Neither the public, the press, nor the U.S. Congress was willing to wait that long.

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