Scientists say it contains a compound that can protect against diabetes, liver disease, strokes and heart attacks.
Extra virgin olive oil is the Mediterranean favourite with a reputation as a panacea for all ills.
British shoppers snap up around 62,000 tonnes of olive oil a year - ten times the amount consumed in 1990. The UK is now the world’s tenth biggest olive oil-consuming nation.
There is substantial evidence consuming it as part of a balanced diet can be beneficial to health but the biological and physiological reasons have been unclear.
But some lower quality versions can be extracted using chemicals, or even diluted with other cheaper oils, so buying the right type is important.
Extra virgin olive oil is extracted using natural methods and standardised for purity. It has a distinctive taste.
Now a study published in Lipids in Health and Disease suggests its health-boosting properties are all down to a chemical called hydroxytyrosol.
It was able to reverse markers of insulin resistance and non-alcoholic fatty liver disease in mice fed on a high-fat diet.
Dr Rodrigo Valenzuela, of the University of Chile, said: “Hydroxytyrosol is a polyphenol found in extra-virgin olive oil, which is known to have antioxidant properties and may play a key role in its health benefits.
“Our research shows that in mice fed on a high-fat diet, hydroxytyrosol exerts a protective effect in the liver.”
His researchers looked at the effects of hydroxytyrosol on specific enzymes in the liver vital for vascular health.
Mice fed on a high-fat diet were shown to have a reduction in these chemicals which was linked to an imbalance in the fatty acid composition of the liver, brain and heart.
But those on the same diet supplemented with hydroxytyrosol showed enzyme activity and fatty acid composition in these three organs which reflected that seen in mice fed a regular diet.
Dr Valenzuela said: “Our study found mice fed on a high-fat diet had signs of non-alcoholic liver disease which we believe has led to the noticeable reduction in enzyme activity in the liver and the negative effects on fatty acid composition in this, and other, organs.
“We also found that the liver showed signs of increased oxidative stress, which we know has links to fatty liver disease.
“It is intriguing that adding a relatively low dose of hydroxytyrosol to the diet was able to reverse these effects, reduce the signs of fatty liver disease, and reduce negative effects seen in the other organs.”
Four groups of 12-14 mice were fed on either a high-fat diet (60% fat) or a control diet (10% fat), with or without supplementation of 5mg hydroxytyrosol per kg body weight, administered orally, for a 12 week period.
Blood and tissue samples were collected at the end of the experiment to study the dietary effects on oxidative stress, fatty acid composition and enzymatic activity in multiple organs.
Analysis of blood samples revealed an increase in cholesterol in mice fed a high fat diet - which can lead to strokes and heart attacks. But these levels were reduced by hydroxytyrosol.
A fatty diet also boosted biological markers, or signs, of insulin resistance in the blood which were reduced by hydroxytyrosol - though not to the levels of mice fed a control diet.
The results strengthen the evidence many of the benefits associated with dietary consumption of extra virgin olive oil may be linked to hydroxytyrosol, said the researchers.
Dr Valenzuela said: “Our results indicate hydroxytyrosol may be a key part of the health benefits of extra virgin olive oil.
“We have demonstrated this compound may offer protection against oxidative stress and detrimental fatty acid composition in the liver, heart and brain caused by a high-fat diet.”
But he pointed out so far the experiments have been carried out only in mice in a controlled environment and more research is required to extrapolate the findings to humans.