Yudkin entered the heart-disease debate in 1957, after Keys published his first series of papers claiming a “remarkable relationship” between fat consumption and coronary heart disease. Yudkin was among those who had taken Keys to task for the limitations of his analysis and his overinterpretation of very limited and unreliable data. Yudkin noted that many factors correlate with heart-disease deaths (not just dietary-fat consumption) one of which happened to be sugar consumption. Yudkin paid attention only to the trends of diet and disease in developed nations, and to heart disease and obesity, rather than the whole slew of chronic diseases, and he decided that sugar itself was the fundamental problem. (Yudkin would distance himself from Cleave by refusing to use the term “refined carbohydrates,” because it “gives the impression that white flour has the same ill effects as sugar,” which he considered grossly misleading.) Through the 1960s, Yudkin published the results of a series of experiments implicating sugar in heart disease. He fed sugar and starch to rats, mice, chickens, rabbits, and pigs, and reported that the sugar, depending on the particular animal involved, raised some combination of cholesterol, triglycerides, and insulin levels. Triglycerides are a form of fat molecule found in the blood, and a series of researchers beginning with Pete Ahrens at Rockefeller University and Margaret Albrink of Yale had suggested that triglyceride levels were a better predictor of heart disease than was cholesterol. (Diabetics, as Joslin had noted, all too often died of atherosclerosis, and they, too, inevitably had high levels of triglycerides.) Yudkin also fed high-sugar diets to college students and reported that it raised their cholesterol and particularly their triglycerides; their insulin levels rose, and their blood cells became stickier, which he believed could explain the blood clots that seemed to precipitate heart attacks.

By the early 1970s, the medical-research community was taking Yudkin’s hypothesis seriously. But now the very existence of Keys’s hypothesis was the primary obstacle to the acceptance of Yudkin’s. If one was right, than the other was very likely wrong. The European research community tended to be open-minded on this question. “Although there is strong evidence that dietary fats, particularly the saturated ones, play an important role in the etiology of [coronary heart disease], there is no proof that they are the only or the main culprit,” wrote Roberto Masironi, an Italian cardiologist who would become president of the European Medical Association. “As regards the relationship of sugars to cardiovascular diseases, it must be borne in mind that these nutrients have common metabolic pathways with fats. Disturbances in carbohydrate metabolism may be responsible for abnormal fat metabolism and may therefore act as a causative factor in the development of atherosclerosis and of coronary disease.”