Olive oil is the traditional symbol of the Mediterranean diet, representing the primary source of fat. Phytochemicals present in olive oil exert different biological activity, including antioxidant, antiallergic, anti-inflammatory, antiviral, antiproliferative, and anticarcinogenic effects. The health benefits attributed to the dietary use of olive oil are specifically related to extra virgin olive oil consumption, which is considered a key bioactive food because of its high nutritional quality. 

Olive oil provides mono-unsaturated fatty acids (MUFAs), tocopherols, polyphenols as long as, low saturated fats and linoleic/alphalinolenic acid. These fats, have been proven to have positive effects on the immune system and inflammatory responses 8.  In comparison to other fatty acids, such as linoleic, palmitic or steric acids, extra virgin olive oil exhibits up to twenty more times in the concentration of MUFAs.

In 2011, the European Food Safety Authority (EFSA) published a scientific opinion paper regarding the intake of polyphenols from olive oil and their possible protective role in blood lipids against oxidative stress, maintenance of normal blood HDL-cholesterol concentrations, maintenance of normal blood pressure, anti-inflammatory properties, positive contribution to the upper respiratory tract health, maintenance of a normal function of gastrointestinal tract and defense against external agents. Accordingly, the panel proposed that 5 mg of hydroxytyrosol and its derivatives (e.g., oleuropein complex and tyrosol) in olive oil should be consumed daily in the context of a balanced diet for sufficient avoidance of oxidative damage [9]. Hydroxytyrosol is thought to be the main antioxidant compound in olives, and believed to play a significant role in the numerous health benefits attributed to olive oil.

Furthermore, a plethora of research papers have proposed the positive implication of olive oil consumption in:

1. Chemopreventive action against certain cancers. A plethora of epidemiological data and studies have repeatedly suggested a protective role of olive oil compounds in several human malignancies, such as breast, colorectal cancer and other types [10–14].

2. Protection against cardiovascular diseases. Except for the paper published by the European Food Safety Authority (EFSA) in 2011, which approved health claims that olive oil  protects by its polyphenols against oxidation of blood lipids and for maintenance of normal blood LDL-cholesterol levels by replacing saturated fats in the diet with oleic acid, the United States Food and Drug Administration has approved the health claim that “scientific evidence suggests that eating about 2 tbsp. (23 g) of olive oil daily may reduce the risk of coronary heart disease due to the monounsaturated fat in olive oil [9]. To achieve this possible benefit, olive oil is to replace a similar amount of saturated fat and not increase the overall number of calories consumed in a day”. Furthermore, several studies have shown the hypotensive effect of olive oil through oleic acid [10,15].

3. Obesity and diabetes. Obesity, is an increasingly widening condition affecting millions of people mainly in developed countries. The phenolic compounds that are widely present in olive oil have inhibitory effects on obesity and diabetes [16]. Moreover, several olive leaf components have been shown to be effective against obesity, by suppressing molecular factors involved in adipogenesis [17].

4. Neuroprotection. A large body of evidence supports the beneficial effects of the Mediterranean diet in preventing neurodegeneration. As the Mediterranean diet is characterized by a high consumption of extra-virgin olive oil it has been hypothesized that olive oil and in particular its phenols, could be responsible for the beneficial effect of the Mediterranean diet 18. Phenols, which can be found in extra virgin olive oil, exert strong antioxidant properties and are able to counteract oxidative stress in brain tissue. Oleuropein and hydroxytyrosol act as direct free radical scavengers, hydroxytyrosol and oleocanthal are strong cyclooxygenases (COX) inhibitors while oleuropein counteracts low density lipoprotein (LDL) oxidations 19.

5. Arthritis. Osteoarthritis is a common degenerative disease of the joints among the elderly. Polyunsaturated fatty acids found in olive oil have been associated with the decrease of systemic inflammation. Furthermore, the oleocanthal found in olive oil inhibits the activity of specific enzymes that cause inflammation. Overall, systematic olive oil intake helps to improve health outcomes, as inflammation is a known factor across a variety of chronic diseases 20–22.

6. Fertility. Recent scientific data suggest that extra virgin olive oil may be beneficial for fertility whether couples are trying to conceive naturally or are undergoing assisted reproductive treatments or in vitro fertilisation. Results from animal models suggest that olive oil dietary supplementation could be an interesting alternative to enhance sperm quality particularly in aged individuals [23].

7. Depression. The effects of olive oil on depression has been of particular research interest as well. Data from patients with severe depression have suggested the beneficial effects of extra virgin olive oil [24]. Overall, several data suggest that fats coming from olive oil, may enhance the central nervous system, helping nerves function properly and increasing levels of the mood-supporting neurotransmitter serotonin.

8. Anti-ageing properties. Vitamin E, which is present in olive oil, aids in minimizing the appearance of wrinkles and fine lines. Additionally, it has antioxidants that help defend against free radicals, which speed up aging. Lab studies show that olive oil has potent anti-inflammatory effects on skin and may act as a shield against UV damage. Additionally, monounsaturated fat, which makes up almost 73% of olive oil, is linked to increasedskin firmness and elasticity [10, 25].