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Cholesterol, the cornerstone of Dr. Keys's theory, is a mysterious yellowish, waxy substance, chemically a crystalline alcohol. Scientists assume that cholesterol (from the Greek chole, meaning bile, and stereos, meaning solid) is somehow necessary for the formation of brain cells, since it accounts for about 2% of the brain's total solid weight. They know it is the chief ingredient in gallstones. They suspect it plays a role in the production of adrenal hormones, and they believe it is essential to the transport of fats throughout the circulatory system. But they cannot fully explain the process of its manufacture by the human liver. Although the fatty protein molecules, carried in the blood and partly composed of cholesterol, are water soluble, cholesterol itself is insoluble, and cannot be destroyed by the body. "A remarkable substance," says Dr. Keys, "quite apart from its tendency to be deposited in the walls of arteries."
When thus deposited, Keys says that cholesterol is mainly responsible for the arterial blockages that culminate in heart attacks. Explains Keys: As the fatty protein molecules travel in the bloodstream, they are deposited in the intima, or inner wall of a coronary artery. The proteins and fats are burned off, and the cholesterol is left behind. As cholesterol piles up, it narrows, irritates and damages the artery, encouraging formation of calcium deposits and slowing circulation. Eventually, says Keys, one of two things happens. A clot forms at the site, seals off the flow of blood to the heart and provokes a heart attack. Or (more commonly, thinks Keys) the deposits themselves get so big that they choke off the artery's flow to the point that an infarct occurs: the heart muscle is suffocated, cells supplied by the artery die, and the heart is permanently, perhaps fatally injured.
Fats & Coronaries. Ordinarily, the human liver synthesizes only enough cholesterol to satisfy the body's needs—for transportation of fats and for production of bile. Even eggs and other cholesterol-rich foods, eaten in normal amounts, says Dr. Keys, do not materially affect the amount of cholesterol in the blood. But fatty foods do.
During World War II, doctors in The Netherlands and Scandinavia noted a curious fact: despite the stresses of Nazi occupation, the death rate from coronary artery disease was slowly dropping. Not until long after the war—1950, in fact—did they get a hint of the reason. That year, Sweden's Haqvin Malmros showed that the sinking death rate neatly coincided with increasingly severe restrictions on fatty foods. That same year the University of California's Dr. Laurance Kinsell, timing oxidation rates of blood fats, stumbled onto the discovery that many vegetable fats cause blood cholesterol levels to drop radically, while animal fats cause them to rise. Here Keys and others, such as Dr. A. E. Ahrens of the Rockefeller Institute, took over to demonstrate the chemical difference between vegetable and animal fats—and even between different varieties of each.