This blog post is reproduced from a post we made on our Facebook page more than three years ago:

Hardly a week goes by without news of another study finding olive oil health benefits. This one by Tsolaki, et al. (2020)  claimed to show brain health benefits for subjects with early dementia. The evidence looked solid – a 12-month randomised controlled trial comparing the effects of Greek High Phenolic Early Harvest Extra Virgin Olive Oil to ordinary EVOO and to a Mediterranean diet. Support from the olive oil industry was acknowledged but that does not necessarily discredit the study. However, some of the language used in the paper did sound like spin, e.g. Greek EVOO has been “extensively suggested as a top nutritional supplement worldwide.”

The study used 12 scales of cognitive function but only found better results for special EVOO versus ordinary EVOO versus Med diet on two or three of these, and some of these barely hit the .05 statistical criteria for a non-random finding. Using many different measurements between groups and reporting those that reach statistical significance is called p-hacking – the more measurements, the more likely it is to find statistically significant differences by chance alone. The number of subjects in this study was small, 50 subjects divided into 3 groups, which increases the probability of any difference being due to chance alone – the authors said that the numbers were small because “the sponsor had no EVOO of the same quality the next year.”

Several problems with this study led us to question the validity of its findings, e.g. the abstract overstates what the study actually found. Also, the study did not give details of the Med diet that all groups were to consume, nor whether there was any difference in adherence between the three groups.

Even if it can be proven that eating high polyphenol EVOO has some protective effect, it needs to be appreciated that many whole plant foods have a much higher polyphenol content than the best olive oil. We prefer to source our phytonutrients from a diversity of nutrient-rich whole plant foods, not a calorie-dense, nutrient-poor plant extract. We would like to see EVOO studies that compare it to phytonutrient-rich whole plant foods such as berries and leafy green vegetables.

Resources

Tsolaki, M., Lazarou, E., Kozori, M., Petridou, N., Tabakis, I., Lazarou, I., . . . Magiatis, P. (2020). A Randomized Clinical Trial of Greek High Phenolic Early Harvest Extra Virgin Olive Oil in Mild Cognitive Impairment: The MICOIL Pilot Study. Journal of Alzheimer’s Disease, 78(2), 801-817.