With the subject of heart disease, however, controversy arrived. Cohen testified that there was no “direct relationship” linking heart disease to dietary fats, and that he had been able to induce the same blood-vessel complications seen in heart disease merely by feeding sugar to his laboratory rats. Peter Cleave testified to his belief that the problem extended to all refined carbohydrates. “I don’t hold the cholesterol view for a moment,” Cleave said, noting that mankind had been eating saturated fats for hundreds of thousands of years. “For a modern disease to be related to an old-fashioned food is one of the most ludicrous things I have ever heard in my life,” said Cleave. “If anybody tells me that eating fat was the cause of coronary disease, I should look at them in amazement. But, when it comes to the dreadful sweet things that are served up…that is a very different proposition.” Yudkin blamed heart disease exclusively on sugar, and he was equally adamant that neither saturated fat nor cholesterol played a role. He explained how carbohydrates and specifically sugar in the diet could induce both diabetes and heart disease, through their effect on insulin secretion and the blood fats known as triglycerides. McGovern now struggled with the difficulty of getting some consensus on these matters.

“Are you saying that you don’t think a high fat intake produces the high cholesterol count?” McGovern asked Yudkin. “Or are you even saying that a person with high cholesterol count is not in great danger?”

“Well, I would like to exclude those rare people who have probably a genetic condition in which there is an extremely high cholesterol,” Yudkin responded. “If we are talking about the general population, I believe both those things that you say. I believe that decreasing the fat in the diet is not the best way of combating a high blood cholesterol…. I believe that the high blood cholesterol in itself has nothing whatever to do with heart disease.”

“That is exactly opposite what my doctor told me,” said McGovern.

“If men define situations as real,” the sociologist William Isaac Thomas observed in the 1920s, “they are real in their consequences.” Embracing a hypothesis based on incomplete evidence or ideological beliefs is risk enough. But this also makes it extremely difficult to entertain alternative possibilities, unless we can reconcile them with what we have now convinced ourselves is indisputable.

By the early 1970s, all potential causes of heart disease, or potentially any chronic disease, had to be capable of coexisting with the belief that dietary fat was the primary cause of coronary heart disease. The notion that refined or easily digestible carbohydrates caused chronic disease could not be so reconciled.