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All natural food fats fall into one of three categories—saturated, mono-unsaturated and polyunsaturated. The degree of saturation depends on the number of hydrogen atoms on the fat molecule. Saturated fats can accommodate no more hydrogens. Mono-unsaturated fats have room for two more hydrogens on each molecule, and the polyunsaturated fat molecule has room for at least four hydrogens.
The three fats have similar caloric values (about 265 calories per oz.), but each exerts a radically different influence on blood cholesterol. Saturated fats in meat and dairy products promote production of cholesterol in quantities too large for the body to excrete. Mono-unsaturated fats (predominant in olive oil, most margarines) have no apparent effect at all on blood cholesterol levels. Polyunsaturated fats, such as those in corn, cottonseed or fish oils, on the other hand, actually lower cholesterol by increasing the excretion of bile acids.
Marbled Meat. Thus, says Physiologist Keys, the big cut in reducing U.S. fat intake should come in the popular saturated fats which, although more expensive, have become a bigger and bigger part of the American diet. Restaurants take pride in heavily marbled meat. Most margarine manufacturers "convert liquid fats into partly saturated solids by "hydrogenating" them—that is, by forcing hydrogen atoms onto the liquid fat molecules. Dairy farmers are paid more for milk with high butterfat content. Keys is a milk drinker himself—but only of modified skim milk that contains a maximum of 2% butterfat.
Proof in Tests. Neither Keys nor anyone else claims to know the whole complex chemical-mechanical story of cholesterol deposition, but he regards the cause-and-effect relationship between cholesterol and heart disease as proved. In 1946, long before Keys suspected that this relationship existed, he and Dr. Henry Taylor persuaded 286 Minneapolis-St. Paul businessmen, then aged 45 to 54, to submit to painstaking, yearly physical examinations. The idea: to see if the onset of ailments in general could be accurately forecast by physiological measurements, i.e., weight, blood pressure, electrocardiogram, cholesterol count. So far, among other diseases, 27 of the businessmen have suffered heart attacks, 16 of them fatal. The common element in 18 of the cases was high (240-360) cholesterol levels. Moreover, it was the only significant common element. The electrocardiograph, says Keys, "doesn't hurt anybody and looks impressive in a doctor's office," but it is a poor predictor of coronary disease.
Later, Keys studied the eating habits and coronary death rates of middle-aged Japanese—in Japan, Hawaii and California. The native Japanese, he reports, get only 13% of their calories from fats. They eat a high-carbohydrate diet of rice, fish and vegetables, have an average cholesterol count of 120. The Hawaiian Japanese, on the other hand, also eat fish, along with meat, eggs and dairy products; they get 32% of their calories from fats, have an average cholesterol count of 183. The Los Angeles Nisei's diet is typically American; they get 45% of their calories from fatty foods, and their average cholesterol count is 213. For every one heart attack in Japan, Keys notes, the Hawaiian Japanese have four, the Los Angeles Nisei ten.