Nutrition Article II

Olive oil and antioxidant properties

Numerous teams of researchers in Europe, Australia and North America have further documented these results. At the same time, they have discovered additional advantages of olive oil (antioxidants and their protective effect against free radicals), stemming from the minor components present in its unsaponifiable fraction (vitamins and antioxidants) (Vázquez Roncero et al., 1973; Montedoro et al., 1974; 1992a and b; 1993; Sato et al., 1990; Papadopoulos and Boskou, 1991; Chimi et al., 1988; 1991; Perrin et al., 1992; Reaven et al., 1993; Galli and Visioli, 1994; 1995; 1996; 1998; Livrea et al., 1995; Servili et al., 1996; Angerosa and Giovacchino, 1996; Baldioli et al., 1996; Litridou et al., 1997; Ryan et al., 1998; Saija et al., 1998; Mataix et al., 1999; Galletti et al., 1996; 1999; Ruiz Gutiérrez et al., 1999). The polyphenols in virgin olive oil may function in vivo as protective antioxidants by exerting a protective effect against LDL oxidation; it is well known that oxidised LDLs are atherogenic whereas normal ones are not (Katan et al., 1999; Cortesi and Fedeli, 1995; 1998; Cortesi et al., 1997; Berra et al., 1995; Jacotot et al., 1998; Wiseman et al., 1996; Jiménez de Blas and del Valle González, 1996a y b; Esterbauer et al., 1990; 1991).

Other oils have a high monounsaturate content but they contain smaller quantities of these polyphenols (Colquhoun et al., 1996). There are oils that are rich in oleic acid, but they all necessarily have to be refined before being eaten. As a result, they do not taste as pleasant as olive oil and are used less often for dressings. Olive oil is the only oil that can be eaten as soon as it is extracted (virgin oil) without refining or industrial processing, which enables it to retain innumerable substances, antioxidants and vitamins that add to its nutritional value. In 1992 Gey et al. reported that olive oil supplied 3-5 times more vitamin E than other vegetable oils. The important protective role of vitamin E was demonstrated in the MONICA project, which reported vitamin E deficiency as a greater cardiovascular risk than blood cholesterol and high blood pressure.

The monounsaturated fatty acids in olive oil make it more resistant to heat. Consequently, olive oil can be re-used for frying without undergoing hydrogenation or isomerisation processes that cancel out its beneficial effects on lipid metabolism. It is the lightest and tastiest fat for frying (Varela et al., 1980; 1984; 1986; 1988; 1996).

In 1985, Mancini et al. studied blood pressure and observed that it was significantly lower when olive oil was consumed regularly, thus confirming the data reported by Aravanis et al. in Greece in 1980. Williams et al. reached the same conclusion in 1987. Recent research (Ferrara et al, 2000) reports that the use of olive oil lowers daily anti-hypertensive dosage requirements, possibly through enhanced nitric oxide levels stimulated by polyphenols.

An olive-oil-rich diet is not only a good alternative in the treatment of diabetes mellitus (Bonanome et al., 1991); it can also prevent or slow down the onset of the disease. It prevents insulin resistance and its possible harmful consequences (Wolever et al., 1999; Mancini et al., 1992), it raises HDL-cholesterol and it lowers blood triglycerides (Lerman-Garber et al., 1994). In addition, it ensures better control of the glucose in the blood (Garg et al., 1988, 1993, 1994) and it lowers blood pressure (Rassmussen et al., 1993). Olive oil significantly improves cell glucose utilisation and lowers triglycerides, andit is more pleasing to the palate than a high-carbohydrate diet containing the same amount of fibre (Campbell et al., 1994).

Epidemiological studies have also revealed that olive oil has a protective effect against some types of malignant tumours (breast, prostate, endometrium, digestive tract…) (Trichopoulou, 1995; 1997; Trichopoulou and Lagiou, 1997; Braga et al., 1998; La Vecchia et al., 1995,1999; Gasull et al., 2000). It adds to the palatability of vegetables, pulses and greens whose beneficial effects in the prevention of cancer have been amply proven (Willett and Trichopoulou, 1996; World Cancer Research Fund, 1997).

Olive oil has been shown to streng then the immune system against external attacks caused by microorganisms such as bacteria and viruses (Peck et al., 1995, 1996,2000), (Álvarez Cienfuegos et al., 1999). A research team at the University of Athens, led by Athena Linos, recently found that regular olive oil consumption reduces the risk of developing rheumatoid arthritis. Although the mechanism is not yet clear, the authors suggest that antioxidants are believed to be behind this beneficial effect. Olive oil is rich in vitamin E, which plays a positive biological role in removing free radicals, which are the molecules involved in certain chronic diseases and in the ageing process. Hence, olive oil is believed to play a part in increasing life expectancy.

Olive oil is also good for the brain, according to the findings obtained by Caruso et al. of the University of Bari in 1999. Olive oil consumption provides protection against deterioration of the cognitive functions related to ageing and age-related memory loss.

In their angiographic OLIVE study Colquhoun and Weyers of the University of Queensland (Australia) are currently finding not only that the Mediterranean diet is effective in preventing secondary coronary events, but also, for the first time, that olive oil has a positive effect on depression. These results take on great importance in the light of the high present-day incidence of depression and the high risk it represents for recurrent coronary heart disease.

Owing to its vitamin E and antioxidant content olive oil has a protective, toning effect on the skin, which is why it is believed to be especially suited for preventing the appearance of skin lesions.

Olive oil appears to play a favourable part in bone calcification and high consumption improves bone mineralisation (Laval-Jeantet et al., 1980).

Olive oil is the fat that is best digested and absorbed; it has excellent properties in this respect and a mild laxative effect that helps to combat constipation (Ricci, 1969). In 1963, Mastrilli and Stocchi confirmed the effect of olive oil as a cholagogue and its cholecystokinetic properties, as did Charbonnier et al. in 1985 and Singer and Pavel in 1959, who concurred on its utility in treating cholecystopathies. To conclude, owing to its effective action on the tonus and activity of the gallbladder, olive oil favours lipid digestion because it is emulsified by the bile and it prevents the appearance of cholesterol gallstones (Massini and Cairella, 1967).

Olive oil is a very healthy nutrient that has a high calorie value, which might lead to the belief that its consumption encourages obesity. Experience shows, however, that people, who consume most olive oil, suffer less from obesity. It has been proven that, when compared with a low-fat diet, an olive oil diet leads to greater and more lasting weight loss. It is tolerated better because it tastes good and makes eating vegetables more enjoyable (Sacks et al., 1999).

The health-related properties of table olives are very similar to those of olive oil. Moreover, recent research conducted by the García-Granados team of the Universidad de Granada and Nájera of the Instituto Carlos III in Madrid has discovered that maslinic acid, which is extracted from the olive, might act as an inhibitor of the AIDS virus. Maslinic acid hinders the spread of HIV by inhibiting the action of an enzyme (serine-protease) that uses the virus to burst the cell walls in which it is established and to spread to new cells. This acid may also have a positive effect in the control of malaria by acting as an anti-inflammatory agent, neuronal activator or hepatic protector.

At the recent 2000 International Conference on the Mediterranean Diet, a Scientific Exchange was held by key nutritionists from all around the world. On reviewing total fat consumption and a global dietary pattern, they drew up a consensus statement in which they expressly acknowledge the advantages of olive oil and confirm its health benefits as the main source of fat in a healthy diet.