By Jane E. Brody
Published: March 24, 1993
ADMONISHED for decades to cut back on saturated fats to lower their cholesterol, millions of Americans made sensible dietary changes that they thought would protect their hearts. They switched from butter to margarine, looked for "made with pure vegetable shortening" on packages of baked and fried products, sought fast foods that were not fried in beef fat and many even gave up eating meat.
And after recent reports that walnuts and olive oil may promote cardiovascular health, many have begun chomping on nuts and sprinkling olive oil on foods as if it were a magical elixir.
But now they are hearing disturbing news that margarine may not be so good for the heart after all, that vegetable shortening is even less advantageous than margarine, that at least some of the saturated fat in red meat does not raise cholesterol but that overdoing the nuts and olive oil can put on pounds that in turn may send cholesterol levels soaring.
It is enough to make a health-conscious person wonder whether to return to the eggs-butter-cream-and-steak diet of yore and let the old ticker fend for itself until scientists make up their minds about what is and what is not healthful for the heart.
But wait. The dietary fat picture is not as confusing as it may seem. And once you understand the science behind recent findings, you will have a rather clear picture of how to put together a diet that helps to prevent not just heart disease, but many cancers and obesity (and its attendant risks of hypertension and diabetes) as well. Fat and Cholesterol
There are three main types of fatty acids -- saturated, monounsaturated and polyunsaturated -- and the various fats in foods are classified by which type of fatty acid predominates. The more saturated fatty acids in a fat, the harder it is at room temperature and, in general, the more damaging it is to serum cholesterol.
Thus, butter, meat fat and the tropical "oils" (coconut, palm and palm kernel) are considered saturated fats because most of their fatty acids are saturated and they are solid at room temperature. Olive oil, canola oil and most of the nut oils, like peanut, walnut and avocado, are monounsaturated. Soybean, corn, safflower, sunflower and cottonseed oils are polyunsaturated.
An unsaturated fat can be made more saturated, and thus firmer, by a process called hydrogenation. This is how margarine and Crisco-type vegetable shortenings are made from liquid vegetable oils. Stick margarines are more fully hydrogenated than soft tub or squeezable margarines.
The method of hydrogenation used by commercial producers of edible fats in this country creates a chemical form called trans fatty acids, which have been shown to raise blood levels of harmful low-density-lipoprotein cholesterol, known as LDL, both in young healthy people with normal cholesterol levels and in middle-aged people who start out with moderately high cholesterol levels.
In a report this month from the continuing Nurses' Health Study at the Harvard School of Public Health, frequent consumption of margarine and vegetable shortening was linked to a 50 percent higher rate of coronary deaths, though the study could not distinguish between the harm that might be caused by trans fatty acids and the damage attributable to the saturated fatty acids in these fats.
But even with unnaturally introduced trans fatty acids, scientists who study fat metabolism have shown that margarine and vegetable shortening are considerably less damaging to cholesterol levels than butter and other natural fats that are highly saturated. Most saturated fats raise blood levels of cholesterol over all and especially those of artery-clogging LDL cholesterol.
An exception is stearic acid, one of the saturated fats in beef fat and the primary fat in cocoa butter, from which chocolate is made. Stearic acid, according to well-designed studies at the University of Texas Southwestern Medical School in Dallas, does not raise or lower cholesterol.
Polyunsaturated oils have been promoted for years as more healthful for the heart because they lower the total cholesterol level in the blood. Unfortunately, they reduce not only harmful LDL cholesterol but also beneficial HDL, or high-density-lipoprotein, cholesterol, a fact that has prompted a recent re-examination of recommendations for a heart-healthy diet.
Monounsaturated fats like olive oil, which had long been thought to have a neutral effect on blood cholesterol, are now known to lower LDL cholesterol while leaving untouched or slightly raising protective HDL cholesterol, which helps to clear fatty deposits from artery walls. This finding fits with the observation that heart disease is relatively uncommon among people living along the Mediterranean, where olive oil is the main cooking and table fat.
But regardless of which fat is studied, the more total fat consumed, the higher the coronary risk is, in part because high-fat diets are associated with overweight and in part because most such diets are filled with artery-damaging saturated fats. Restructuring Diet
First and foremost, your goal should be to reduce the amount of fat you consume over all. For average Americans this means eating about a third less fat. This is accomplished by choosing mainly low-fat foods, cooking with little or no fat and adding as little fat as possible to prepared foods. Certain sources of saturated fats, like lean meat and chocolate in circumspect amounts, can remain part of a heart-healthy diet, but others, like butterfat, lard, suet, tropical oils and chicken fat, are best avoided whenever possible.
Experts say that even with trans fatty acids, margarine is still preferable to butter as a table spread. But the ideal choice is to quit smearing your bread with fat (tasty whole-grain breads need no embellishment), second best is to adopt the Italian custom and use olive oil, and third is to use the reduced-fat tub or squeezable margarines, which are less saturated and have fewer trans fatty acids than stick margarine.
Also watch out for hydrogenated vegetable oils. Check ingredient lists on packaged foods for the words "partially hydrogenated" or "hydrogenated" vegetable oil. Unfortunately, the same kind of information is not available to consumers of commercially prepared foods that are sold without an ingredients list, like fast foods and restaurant foods that are fried or sauteed and bakery goods (cookies, cakes, muffins, pies, danishes) that are made with fat. All such products can contain substantial amounts of hydrogenated fats and suspect trans fatty acids.
Remember that body weight is a major contributor to high cholesterol and coronary risk. If you fail to lose weight when shifting to a low-fat diet, you cannot expect much change in your cholesterol level. As Dr. Scott Grundy of Southwestern Medical School put it, "It's not just a question of what you eat but of how much you eat."
Graph: "What Kinds of Fat Are You Eating?" shows amounts of each type of fat in selected foods (Sources: Consumer Report on Health, United States Department of Agriculture) Drawing