Good Calories, Bad Calories

But there were caveats. As the men aged, those who succumbed to heart disease were ever more likely to have low cholesterol (as had Eisenhower) rather than high cholesterol. The cholesterol/heart-disease association was tenuous for women under fifty, and nonexistent for women older. Cholesterol has “no predictive value,” the Framingham investigators noted in 1971. This means women over fifty would have no reason to avoid fatty foods, because lowering their cholesterol by doing so would not lower their risk of heart disease. None of this was deemed relevant to the question of whether Keys’s hypothesis was true.

The dietary research from Framingham also failed to support Keys’s hypothesis. This never became common knowledge, because it was never published in a medical journal. George Mann, who left the Framingham Study in the early 1960s, recalled that the NIH administrators who funded the work refused to allow publication. Only in the late 1960s did the NIH biostatistician Tavia Gordon come across the data and decide they were worth writing up. His analysis was documented in the twenty-fourth volume of a twenty-eight-volume report on Framingham released in 1968. Between 1957 and 1960, the Framingham investigators had interviewed and assessed the diet of a thousand local subjects. They focused on men with exceedingly high cholesterol (over 300) and exceedingly low cholesterol (under 170), because these men “promised to be unusually potent in the evaluation of dietary hypotheses.” But when Gordon compared the diet records of the men who had very high cholesterol with those of the men who had very low cholesterol, they differed not at all in the amount or type of fat consumed. This injected a “cautionary note” into the proceedings, as the report noted. “There is a considerable range of serum cholesterol levels within the Framingham Study Group. Something explains this inter-individual variation, but it is not diet (as measured here).”

“As measured here” encapsulates much of the challenge of scientific investigation, as well as the loophole that allowed the dietary-fat controversy to evolve into Henry Blackburn’s two strikingly polar attitudes. Perhaps the Framingham investigators failed to establish that dietary fat caused the high cholesterol levels seen in the local population because (1) some other factor was responsible or (2) the researchers could not measure either the diet or the cholesterol of the population, or both, with sufficient accuracy to establish the relationship.

As it turned out, however, the Framingham Study wasn’t the only one that failed to reveal any correlation between the fat consumed and either cholesterol levels or heart disease. This was the case in virtually every study in which diet, cholesterol, and heart disease were compared within a single population, be it in Framingham, Puerto Rico, Honolulu, Chicago, Tecumseh, Michigan, Evans County, Georgia, or Israel. Proponents of Keys’s theory insisted that the diets of these populations were too homogenous, and so everyone ate too much fat. The only way to show that fat was responsible, they argued, was to compare entirely different populations, those with high-fat diets and those with low-fat diets. This might have been true, but perhaps fat just wasn’t the relevant factor.

Ever since Sir Francis Bacon, in the early seventeenth century, scientists and philosophers of science have cautioned against the tendency to reject evidence that conflicts with our preconceptions, and to make assumptions about what assuredly would be true if only the appropriate measurements or experiments could be performed. The ultimate danger of this kind of selective interpretation, as I suggested earlier, is that a compelling body of evidence can be accumulated to support any hypothesis. The method of science, though, evolved to compel scientists to treat all evidence identically, including the evidence that conflicts with preconceptions, precisely for this reason. “The human understanding,” as Bacon observed, “still has this peculiar and perpetual fault of being more moved and excited by affirmatives than by negatives, whereas rightly and properly it ought to give equal weight to both.”

To Keys, Stamler, Dawber, and other proponents of the dietary-fat hypothesis, the positive evidence was all that mattered. The skeptics considered the positive evidence intriguing but were concerned about the negative evidence. If Keys’s hypothesis was incorrect, it was only the negative evidence that could direct investigators to the correct explanation. By the 1970s, it was as if the two sides had lived through two entirely different decades of research. They could not agree on the dietary-fat hypothesis; they could barely discuss it, as Henry Blackburn had noted, because they were seeing two dramatically different bodies of evidence.