Ahrens chose a nine-member task force representing the full range of scientific views on the diet-heart hypothesis. The panel deliberated for several months over each link in the chain of the diet-heart hypothesis, from eating saturated fat, to total cholesterol, to heart disease. The results, however, were not exactly welcome news to diet-heart supporters like Hegsted or Keys. For instance, one issue the panel agreed upon was that the evidence condemning saturated fat was not persuasive. Moreover, the most they could say about fat generally was that it could be linked to heart disease only indirectly. The core problem was, as it had always been, the near-absence of clinical trial data on the low-fat diet, leaving only epidemiological studies. These studies, as we know, could show association but not prove causation. They had been enough for the Hegsted camp but not for the Ahrens camp.

The final report from the Ahrens task force in 1979 made it clear that the majority of its members remained highly skeptical of the idea that reducing fat or saturated fat could deter coronary disease. The group hadn’t explicitly said that the dietary goals would do harm, however, and so Hegsted chose to take this as a green light. Using the same tenuous logic as did Keys in assuming that he was right until proven wrong, Hegsted asked rhetorically: “The question . . . is not why should we change our diet, but why not? What are the risks associated with eating less meat, less fat, less cholesterol?” The view in ascendance among nutrition experts was that Americans should “hedge their bets” against heart disease by reducing dietary fat until more evidence emerged. Hegsted imagined that “important benefits could be expected,” and he could not imagine the costs. Ahrens’s committee countered that the principle of “doing no harm” demanded harder proof before proceeding with a change in the American diet, but Hegsted was not persuaded by this argument. And ultimately, the USDA was accountable not to academic scientists but to the US Congress, which had ruled definitively in favor of a new low-fat regime.