Consider Keys’s cholesterol hypothesis as an example of this logic. One reason we came to believe that high cholesterol is a cause of heart disease is that severe atherosclerosis is a common symptom of genetic disorders of cholesterol metabolism. If having a cholesterol level of 1,000 mg/dl—as these individuals often do—makes atherosclerosis seemingly inevitable, the logic goes, and if higher cholesterol seems to associate with higher risk of heart disease among the rest of us, then cholesterol is a cause of heart disease, and elevating cholesterol by any amount will increase risk. The higher the cholesterol, the greater the risk. If eating saturated fat elevates cholesterol, then that in turn causes heart disease. And this is supposedly true of diabetics as well. Keys oversimplified the science and was wrong about the true relationship of cholesterol and heart disease, but the logic itself is otherwise sound.

The same logic holds for blood pressure and heart disease. The higher the blood pressure, the greater the risk of heart disease. If salt supposedly raises blood pressure, even if only by a few percentage points, then salt is a nutritional cause of heart disease. This, too, is held to be true for diabetics. Thus, the atherogenic American diet, as now officially defined, the diet that clogs arteries and causes heart disease, is a diet high in saturated fat and salt.

Now let’s apply the same reasoning to metabolic syndrome and diabetes. Diabetics suffer more virulent atherosclerosis and die of heart disease more frequently than those with metabolic syndrome, and much more frequently than healthy individuals who manifest neither condition. Some aspect of the diabetic condition must be the cause—most likely, either high blood sugar, hyperinsulinemia, or insulin resistance, all three of which will tend to be worse in diabetics than in those with metabolic syndrome. Indeed, the existence of metabolic syndrome tells us that these same abnormalities exist in nondiabetics, although to a lesser extent, and though individuals with metabolic syndrome suffer an increased risk of heart disease, they do so to a lesser extent than diabetics. And because dietary carbohydrates and particularly refined carbohydrates elevate blood sugar and insulin and, presumably, induce insulin resistance, the implication is that eating these carbohydrates increases heart-disease risk not only in diabetics but in healthy individuals. By this reasoning, the atherogenic American diet is a carbohydrate-rich diet. Hence, cognitive dissonance.