In the fight against heart disease, olive oil may be a better weapon than popular polyunsaturated oils like corn oil and safflower oil.

A new study comparing the effects of different types of fats on cholesterol levels in the blood showed that both monounsaturates such as olive oil and polyunsaturates result in markedly lower cholesterol levels, as opposed to the saturated fats in meats, egg yolks and dairy products, which raise cholesterol levels. But monounsaturates are preferable because they are just as effective as polyunsaturates, do not have the possible side effects of polyunsaturates and may actually be superior in lowering certain types of cholesterol.

"We knew that the rate of cardiovascular disease was very low in the Mediterranean region where people cook primarily with olive oil," says Dr. Scott M. Grundy, director of the Center for Human Nutrition at The University of Texas Health Science Center at Dallas. "But insufficient work has been done on the ability of monounsaturated fats to lower cholesterol levels and the way they would compare with polyunsaturates."

Fifteen years ago, Dr. Ancel Keys and his colleagues at the University of Minnesota conducted a 10-year study of middle-aged men in seven countries, correlating the kinds and quantities of fat in their diets with their risk of dying from cardiovascular disease. Aside from Japan, where diets contained very low quantities of fat, the people in the Mediterranean area had less heart disease than any other area; yet they consumed just as high a percentage of their calories in fat as the people in northern Europe, Canada and the United States.

To test the cholesterol-lowering efficiency of monounsaturates, Grundy and his partner in the research, Dr. Fred H. Mattson of the Department of Medicine, University of California-San Diego in La Jolla, conducted clinical studies over a two-year period at the Veterans Administration Medical Centers in Dallas and San Diego.

Grundy and Mattson devised three liquid diets that differed from one another only in the type of fat--saturated, monounsaturated or polyunsaturated. The fat in these diets made up 40 percent of their total calories. Twenty patients consumed the three liquid diets sequentially, remaining on each diet for four weeks. The patients' blood was tested for total cholesterol and total triglycerides, as well as for HDL, LDL, and VLDL, which are the lipoproteins that make up the total cholesterol level.

As expected, the patients' cholesterol levels were highest on the saturated-fat diet. Also as expected, the polyunsaturated-fat diet lowered the total cholesterol level, the LDL level and the HDL level in the blood.

"Lowering the level of low-density lipoproteins (LDL) is very desirable," explained Grundy. "LDL delivers cholesterol to many tissues throughout the body; but as LDL circulates, some of it may enter the walls of the arteries to form atherosclerotic plaques. These plaques obstruct blood vessels, which may cause a heart attack. The higher the LDL level, the more rapid the development of atherosclerotic plaques."

"The blood cholesterol also can be carried in high-density lipoproteins (HDL). HDL plays a role in removal of cholesterol from tissues. It may help to rid the artery wall of excess cholesterol, which will slow down the growth of plaques. Therefore, a high level of HDL appears to protect against heart attack. Unfortunately, polyunsaturated fatty acids lower the HDL levels."

Grundy and Mattson found that the monounsaturates lowered the total cholesterol and the LDL as effectively as the polyunsaturates. But monounsaturates did not lower the HDL so often. "This area of the study was not conclusive, but it was very promising," says Grundy.
Grundy believes that Americans would be wise to place more emphasis on monounsaturated than on polyunsaturated fats in their diets. Monounsaturated fats are synthesized naturally by the body, which suggests that they are not inherently harmful. Furthermore, as the major constituent of olive oil, they have a long history of demonstrated safety in a large population group.

"Animal experiments with polyunsaturates have indicated some possible side effects, like promoting the development of cancer, suppressing the immune system and changing cell membranes drastically," said Grundy. "We're not saying that monounsaturates should replace polyunsaturates completely. The body requires a small amount of polyunsaturated oil--it's what we call an essential fatty acid. Our problem with polyunsaturates is giving large amounts."

Concluded Grundy, former chairman of the Nutrition Committee of the American Heart Association, "It would be prudent to limit cholesterol intake to 250-300 milligrams per day and to limit the calories supplied by fats to 30 percent of total calories. At that level, saturates should be kept below 10 percent of total calories, monounsaturates should be at 10-15 percent of calories and polyunsaturates at 5-10 percent." Adopting this prudent approach to diet early in life should help individuals maintain a desirable blood cholesterol level: less than 180 milligrams per deciliter for people in their 20s and less than 200- mg/dl for those 30 and over. Currently, typical cholesterol levels for middle-aged American are 220 to 260 mg/dl.