The proponents of Keys’s hypothesis agreed in principle, but felt they had an obligation to provide their patients with the latest medical wisdom. Though their patients might appear healthy at the moment, they could be inducing heart disease by the way they ate, which meant they should be treated as though they already had heart disease. So these doctors prescribed the diet that they believed was most likely to prevent it. They believed that withholding their medical wisdom from patients might be causing harm. Though Keys, Stamler, and like-minded physicians respected the philosophy of their skeptical peers, they considered it a luxury to wait for “final scientific proof.” Americans were dying from heart disease, so the physicians had to act, making leaps of faith in the process.

This optimistic philosophy was evident early in the controversy. In October 1961, The Wall Street Journal reported that the NIH and the AHA were planning a huge National Diet-Heart Study that would answer the “important question: Can changes in the diet help prevent heart attacks?” Fifty thousand Americans would be fed cholesterol-lowering diets for as long as a decade, and their health compared with that of another fifty thousand individuals who continued to eat typical American diets. This article quoted Cleveland Clinic cardiologist Irving Page saying that the time had come to resolve the conflict: “We must do something,” he said. Jeremiah Stamler said resolving the conflict would “take five to ten years of hard work.” The article then added that the AHA was, nonetheless, assembling a booklet of cholesterol-lowering recipes. The food industry, noted The Wall Street Journal, had already put half a dozen new cholesterol-lowering polyunsaturated margarines on the market. Page was then quoted saying, “Perhaps all this yakking we’ve been doing is beginning to take some effect.” But the yakking, of course, was premature, because the National Diet-Heart Study had yet to be done. In 1964, when the study still hadn’t taken place, a director of the AHA described its purpose as the equivalent of merely “dotting the final i” on the confirmation of Keys’s hypothesis.

This is among the most remarkable aspects of the controversy. Keys and other proponents of his hypothesis would often admit that the benefits of cholesterol-lowering had not been established, but they would imply that it was only a matter of time until they were. “The absence of final, positive proof of a hypothesis is not evidence that the hypothesis is wrong,” Keys would say. This was undeniable—but irrelevant.