Golden oil of the Mediterranean; it may be worth even more than gold to your body.

Golden Oil of the Mediterranean

Asia Minor is generally regarded as the first home of the olive tree, Olea europaea. While the Greeks were largely responsible for introducing the olive tree to Western Europe thousands of years ago, the Spanish are credited with bringing it to the Americas in the sixteenth century. The olive tree is a very hardy plant, surviving in rather dry and unproductive soils.

Oil production. Ninety-eight percent of the world's olive trees grow in the Mediterranean region, with Spain, Italy, Greece, and Turkey the major producers of both table olives and olive oil. Of the 8 million metric tons of olives harvested each year, 92 percent of the fruit is used for oil production, which is about 5 percent of the world's output of vegetable oil.

To produce the highest quality oil, it is important that the olives be picked and processed as soon as the ripen. Harvested olives are ground to a thick paste, then compressed to release the rich, green-gold oil. It requires about five pounds of fruit to produce a pound of oil. There are many varieties of olives, each possessing its own flavor, which in turn produce oils with a wide range of flavors.

California produces almost all of the olives grown in the United States. Most are canned. While 96 percent of the calories in a canned olive come from fat, each ripe olive contains about 20 calories. Green olives, which are picked in the fall before they reach maturation, have less than half the calories of black, mature olives.

Olive oil used in the United States comes largely from Italy and Spain. Olive oil tends to be more expensive than other vegetable oils because so much labor is required to harvest the fruit.

Today there is considerable consumer interest in olive oil since it has a low saturated fat content and a high content of unsaturated fat. Olive oil is different from most other vegetable oils in that its unsaturated fat is largely monounsaturated fat rather than polyunsaturated fat.

Seven-country study. During the 1950s Ancel Keys of the University of Minnesota undertook a study of the diet and health of five European countries (Finland and the Netherlands from Northern Europe, and Italy, Greece, and Yugoslavia from Southern Europe) and compared the data with that of similar studies in the United States and Japan.

In this seven-country study, Dr. Keys found a very strong relationship between the percentage of calories in the diet that came from saturated fats and the incidence of heart disease. Countries with a high incidence of heart disease (the United States and Northern Europe) had high saturated fat intakes (18 to 20 percent of calories), high serum cholesterol levels (230 to 260 milligrams per deciliter) and death rates from heart disease that were two to seven times the rates seen in the Mediterranean countries, where saturated fat intakes were low (5 to 9 percent of calories) and cholesterol levels were below 200 milligrams per deciliter.

Studies of middle-aged men on the Greek islands of Crete and Corfu revealed death rates from heart disease low enough to be comparable to the death rates in regions of Japan where traditional diets contain very low levels of saturated fat (3 percent) and total fat intakes of less than 10 percent of the calories. While Mediterranean diets generally contain substantial amounts of fat (30 to 35 percent), they are low in saturated fat, because of the predominant use of olive oil, rather than fats of animal origin, in the diet. In Dr. Keys' study, age-standardized death rates from all causes were low in those communities in which olive oil was the main fat consumed.

Good for the blood vessels. European scientists have been foremost in demonstrating the beneficial effects to the cardiovascular system of olive oil in the diet. Italian researchers demonstrated that an olive oil-rich diet produced a hypocholesterolemic effect (reduced LDL and total cholesterol levels) similar to that of corn oil, while Dutch scientists have shown that an olive oil-based diet produced beneficial decreases in blood pressure and blood lipids to the same degree as a low-fat, complex carbohydrate-rich diet.

Two additional advantages observed with the use of olive oil were that blood glucose levels declined and the HDL cholesterol (the "good cholesterol") levels were unchanged. This is in contrast to polyunsaturated oils, which normally produce a decline in both LDL and HDL levels.

The above findings were recently confirmed by the Italian Nine Community Study of risk factors for altherosclerosis, in which 4,903 middle-aged Italians were studied. Consumption of olive oil was associated with lower blood cholesterol and blood glucose levels, and lower blood pressures. A diet rich in olive oil can enhance the production of beneficial prostacyclin, which protects against the formation of blood clots and helps lower blood pressure. It has been suggested that olive oil may also favorably influence the peripheral utilization of insulin, thus helping to lower blood glucose levels.

Less cancer. In experimental animals that have chemically induced tumors, high-fat diets increase the incidence of both mammary and colon tumors. However, this is not the case when olive oil is used. High-fat diets utilizing olive oil did not enhance tumor growth; the growth is more like that seen with low-fat feedings.

International comparisons support the evidence from the animal experiments. Human diets in which olive oil is the main source of fat are associated with a reduced risk of cancer. The incidence of breast and bowel cancers is much lower in the Mediterranean countries of Spain and Greece than Scotland and Denmark.

More protection. One might ask "Are there any other interesting substances present in olive oil that might exert a role in decreasing the risk of chronic diseases?" Because olive oil is obtained by a mild extraction method, it retains substantial amounts of active compounds, such as tocopherols (vitamin E), sterols, polyphenols, and more than 100 flavor compounds.

Olive oil contains up to 150 parts per million (ppm) of vitamin E. This natural antioxidant can inhibit platelet aggregation and hence reduce the risk of the formation of blood clots. The ratio of vitamin E to polyunsaturated fat (PUFA) in olive oil is much more favorable than the ratios in other vegetable oils, since olive oil has a much lower PUFA content and the vegetable seed oils lose a considerable amount of their vitamin E content during commercial production of the oil.

Beta-sitosterol, the major sterol in olive oil, is believed to block cholesterol absorption. Olive oil may contain as much as 2,500 ppm of this sterol. Another sterol found in olive oil, cycloartenol, aids in the excretion of cholesterol through increased bile acid secretion.

Various water-soluble polyphenols are found in olive pulp. These are responsible for the bitter taste of olives. Quantities of these compounds end up in the extracted oil. The major polyphenols, tyrosol and 3-hydroxytyrosol, are found at levels of 120 to 150 ppm. These powerful antioxidants can destroy peroxides in the cell, thus enhancing the synthesis of beneficial prostacyclin, and protecting the cell against cancer-forming substances. Polyphenols have also been shown to lower blood glucose levels.

Europeans have attributed additional properties to olive oil relative to the digestive system, such as the beneficial effect on the tone and function of the gall bladder. It use is not associated with gallstone formation as is sometimes the case with polyunsaturated oils. Sorentino reports that olive oil exerts a local protective and ameliorating effect on the inner surface of the stomach and intestines.

Physical properties. Deterioration of olive oil at high cooking and frying temperature is very minimal. This stability results from its low PUFA content, its high content of antioxidants, and its high smoke point (210[degrees] F).

The color of olive oil varies from light yellow to green-yellow to green, depending on the maturity of the olives and the amount of processing used. Olive oil is classified and sold according to the physical treatment that it has received. Virgin olive oil is produced from sound olives by mild mechanical methods that do not lead to any alterations in the oil. Extra virgin olive oil has very little free oleic acid present (a measure of its rancidity), and it possesses a perfectly fruity flavor and odor. Virgin olive oil is considered as a pure fruit juice by the Southern Europeans, and many farmers in Greece consume a wineglass of olive oil for breakfast.

Olive oil may be refined to remove excessive acidity, excessive color, or a strong flavor or odor. The refined oil is then usually blended with some virgin olive oil and marketed as "pure olive oil," which has a fairly bland taste.

From the data presented above we have seen that a modest use of olive oil can be associated with certain health benefits. The increased life expectancy and low rates of chronic diseases, such as heart disease, among Southern Europeans may be attributed in part to their Mediterranean diet, which includes the use of olive oil, cereal foods, fresh fruit, and vegetables.

Winston J. Craig, Ph.D., R.D., is professor of nutrition at Andrews University, Berrien Springs, Michigan.