3 min read
Olive oil sits at the centre of the Mediterranean diet. But is it the oil itself that matters, or the whole way of eating around it?
A 2023 review in Nutrients set out to look at exactly that.
What did the researchers do?
They searched three major databases for randomised controlled trials published between 2000 and 2022. Of 281 papers, 34 met their criteria. Each compared extra virgin olive oil with other fats, low-fat diets or refined olive oil, looking at blood pressure, cholesterol, blood glucose and body weight.
It's a narrative review, which means the authors summarised the studies rather than pooling their numbers.
What did they find?
The picture is encouraging, but not simple.
Some trials found differences in these markers when extra virgin olive oil was compared with other fats or low-fat diets. Others didn't. In a few, other oils performed as well or better on certain measures.
One theme came up again and again: polyphenols. In the trials that compared oils with different phenolic content, the oils richer in these compounds tended to show more of the differences the researchers looked for.
The authors concluded that polyphenols, rather than monounsaturated fat alone, are the likelier explanation.
Why does it matter which olive oil?
The authors point out that refined olive oil and extra virgin olive oil have similar fatty acid profiles. What separates them is the polyphenol content, which is shaped by the olive variety, harvest timing and how the oil is made and stored. They also note that polyphenols fall as oil ages, so freshness matters.
Is there an official health claim for olive oil polyphenols?
There is one.
Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress.
That wording is set by regulation, and it comes with conditions. The oil must contain at least 5mg of hydroxytyrosol and its derivatives per 20g, and the benefit is obtained with a daily intake of 20g of olive oil (roughly a tablespoon and a half).
It's the only health claim authorised for olive oil polyphenols. That's why we describe what the research found rather than promising outcomes, and why polyphenol content, not the label alone, is worth asking about.
What should we keep in mind?
- Most trials were short, and many involved healthy participants.
- Most took place in Europe, where olive oil is already part of daily life.
- Many studies didn't report the oil's polyphenol content, so 'extra virgin' on its own doesn't tell us how much was in the bottle.
- Around half the trials weren't blinded, which is common in food research.
Conclusion
So the honest conclusion is a measured one: this review suggests the polyphenols in extra virgin olive oil are an important part of the story, and it calls for more research with better-characterised oils.
Source: Flynn MM, Tierney A, Itsiopoulos C. Nutrients. 2023;15(13):2916. doi:10.3390/nu15132916
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