Extra virgin instead of refined: how extra virgin olive oil protects the brain through the gut

In the large PREDIMED-Plus study (656 elderly people aged 55–75 with metabolic syndrome), participants consumed olive oil regularly for two years. Those who chose extra virgin (unrefined, first cold-pressed) showed noticeable improvements in cognitive functions. In those who more often used refined oil, memory and attention test results either stayed the same or slightly worsened.

The mechanism turned out to be unexpected. Extra virgin oil is rich in polyphenols—powerful bioactive substances that are lost during refining. These compounds change the composition of the gut microbiota: they increase the diversity of beneficial bacteria and suppress harmful ones. The bacterium Adlercreutzia stood out especially—its growth directly correlated with improvements in cognitive performance.

"We have shown for the first time that the effect of olive oil on the brain occurs precisely through the microbiota," note the authors from Universitat Rovira i Virgili. "The difference between extra virgin and refined was significant even with the same amount of oil in the diet."

Extra virgin first cold-pressed oil retains hundreds of polyphenols that act as prebiotics for good bacteria. Refined oil, while remaining a healthy fat, contains almost none of these substances. As a result, the microbiota of participants who preferred extra virgin became more diverse and "healthy," while that of refined oil lovers became poorer.

The study lasted two years and was part of a large randomized controlled project. This is one of the most convincing pieces of evidence for the "diet—microbiota—brain" link in humans.

The practical takeaway is simple: if you're already using olive oil, it makes sense to switch to extra virgin. The price difference isn't that big, and the effect on the brain and gut can be noticeable within a few months of regular consumption.

Of course, this isn't a panacea and doesn't replace other factors—physical activity, sleep, and overall diet quality. But for older people who want to keep a clear mind as long as possible, switching to real unrefined extra virgin olive oil seems one of the most accessible and enjoyable ways to support the brain.

The paper was published in the journal Microbiome in April 2026.

Source: Martínez-González M.Á. et al. Total and different types of olive oil consumption, gut microbiota, and cognitive function changes in older adults. Microbiome 14, 78 (2026). https://doi.org/10.1186/s40168-025-02306-4 Press release from Universitat Rovira i Virgili and ScienceDaily (April 17, 2026).