Good Calories, Bad Calories

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.”

In the United States, however, Keys’s hypothesis ruled. Keys himself went after Yudkin in a letter that he first distributed widely to investigators in 1970, before it was published in the journal Atherosclerosis. Keys called Yudkin’s arguments for the role of sugar in heart disease “tendentious” and his evidence “flimsy indeed” he treated Yudkin as a figure of ridicule. What made Keys’s critique so ironic, though, is that virtually every argument that he invoked to criticize Yudkin’s hypothesis had been used in the past as criticism of his own. Most were equally valid for both, and spoke to the flaws in the epidemiologic evidence—the use of international cause-of-death statistics and food-consumption data or dietary-recall surveys to draw conclusions about cause and effect—rather than to the actual validity of the hypotheses. Keys’s case against Yudkin eventually came to rest almost entirely on his invocation of the Seven Countries Study as support for his hypothesis. In fact, the Seven Countries Study had been one of the very few studies that had measured sugar consumption in its populations, and sugar indeed turned out to predict heart-disease rates as well as saturated fat did.

By the early 1970s, Keys’s dietary-fat hypothesis of heart disease, despite the ambiguity of the evidence, was already being taught in textbooks and in medical schools as most likely true. After Yudkin retired in 1971, his hypothesis effectively retired with him. His university replaced him with Stewart Truswell, a South African nutritionist who was among the earliest to insist publicly that Keys’s fat theory of heart disease was assuredly correct and that it was time to move on to modifying the diets of the public at large accordingly. Truswell believed it was more important for the prevention of heart disease to convince the public to eat more onions, for their reported ability to alter the “tendency to thrombosis,” than to eat less sugar.