Published 21st May 2026
Olive oil, the gut microbiome, and brain aging: What a 2-year study revealed
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A recent study followed older adults for 2 years to explore links between olive oil, the gut microbiome, and thinking (cognitive) skills.
Higher virgin olive oil intake was associated with better preservation of cognitive skills and greater gut microbiome diversity.
The results suggest the gut microbiome may partially mediate the relationship between virgin olive oil intake and cognitive change.
Because the study is observational, it doesn't prove that virgin olive oil prevents dementia, nor that changing your microbiome will protect your brain.
Olive oil is often treated as a cornerstone of brain-healthy eating, especially in Mediterranean-style diets.
But olive oil isn’t one uniform product: The way it’s processed changes its composition, including its levels of polyphenols and other compounds that may interact with the gut microbiome.
In this article, we break down a 2026 study published in the journal Microbiome that followed older adults for 2 years.
It examined whether different types of olive oil were linked with changes in cognitive function, and whether the gut microbiome might help explain any association.
Below, we outline what the scientists measured, what they found, the study's limitations, and how you can apply the findings to your life today.
What did the study investigate?
This study didn’t test olive oil as a treatment; instead, it followed people in real life to see what patterns emerged over time.
Researchers tracked 656 adults aged 55–75 who were living with overweight or obesity and metabolic syndrome, but were cognitively healthy at the start.
At baseline, participants reported what they typically ate using a detailed food questionnaire (including different types of olive oil, like virgin and more refined “common” olive oil).
They also provided a stool sample to measure gut microbiome diversity and the relative abundance of specific microbes.
Participants completed a set of cognitive tests at the beginning and again 2 years later.
The researchers then examined whether olive oil intake was associated with changes in thinking skills over time, differences in the gut microbiome, and whether microbiome changes might mediate the relationship between olive oil and cognitive health.
Key findings
1. Virgin olive oil intake was linked with better cognitive health
People who consumed more virgin olive oil tended to show more favorable changes in general cognitive function across the 2-year follow-up.
2. Common olive oil intake showed the opposite pattern
Higher intake of common olive oil was associated with lower gut microbiome alpha diversity and accelerated cognitive decline over 2 years.
3. The microbiome might explain part of this effect
The researchers ran additional analyses that suggested the gut microbiome could help explain some of the link between higher virgin olive oil intake and better cognitive change over time.
They highlighted the microbe Adlercreutzia as a potential contributor to this pathway because it showed up as a key “mediator” in their analyses.
More broadly, they think that microbes like this may influence how we process plant compounds in the gut, producing by‑products that can affect signals along the gut–brain axis.
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Why might olive oil and the microbiome affect brain health?
Researchers are increasingly interested in the gut–brain axis, the idea that gut microbes (and the compounds they produce) can influence inflammation, metabolism, and, ultimately, brain function.
One reason olive oil could fit into this picture is that virgin (especially extra-virgin) olive oil tends to contain more polyphenols and other bioactive compounds than more refined oils, and some of these reach the colon where they can interact with gut bacteria.
In turn, microbes produce compounds (metabolites) that may influence inflammation and blood-vessel function, both of which are relevant for cognitive aging.
Olive oil intake is also often linked with better cardiometabolic health in broader research, and since cardiometabolic and brain health are closely connected, this might explain some of the link.
That said, these are still hypotheses, and this study alone can’t confirm which (if any) of these mechanisms is driving the association.
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What are the limitations?
This study has several strengths, including a large sample size, a 2-year follow-up, detailed cognitive tests, and gut microbiome data. However, there are also important reasons to interpret the findings cautiously.
This is an observational study, so it can show associations but can’t prove that olive oil is the primary cause of changes in cognition.
There’s also the risk of residual confounding. For instance, people who eat more virgin olive oil may differ from non-consumers in other ways that are hard to fully account for.
This might include their overall diet quality, lifestyle, income, and so on.
One example the researchers identified was that people who consumed the most common olive oil were more likely to smoke and have lower levels of education than those who consumed virgin olive oil.
Also, diet was assessed using a food frequency questionnaire, which relies on participants' memory and ability to estimate portion sizes, potentially introducing errors.
On the microbiome side, the researchers used a technique called 16S. This method has the potential to misclassify bacteria and doesn’t tell us as much about what microbes are actually doing.
Finally, because the participants lived in the Mediterranean, where olive oil, especially virgin olive oil, is widely consumed, the results may not translate directly to populations with different diets or baseline health risks.
Practical takeaways
If you already use olive oil, consider opting for extra-virgin/virgin more often. The broader evidence base supports it as a healthy fat choice, and this study suggests it may be preferable to more refined olive oils.
Pair olive oil with a fiber-rich diet (vegetables, legumes, whole grains, nuts) as fiber is one of the best ways to support your gut microbiome.
Summary
A 2-year observational study in older adults found that virgin olive oil intake was associated with better cognitive preservation and a more favorable gut microbiome profile.
Conversely, common olive oil intake was associated with lower microbiome diversity and faster cognitive decline. The gut microbiome may partially mediate the relationship, but causality remains unproven.
FAQs
1) Does olive oil improve memory or prevent dementia?
This study suggests an association between higher virgin olive oil intake and better cognitive outcomes over time, but that doesn't prove causation, or that olive oil prevents dementia.
2) What’s the difference between virgin and “common” olive oil?
Virgin (and extra-virgin) olive oil is less processed and typically retains more naturally occurring, healthy compounds (including polyphenols). Common olive oil is generally more refined.
3) What does “microbiome diversity” actually mean?
Microbiome alpha diversity is a way of summarizing how many different microbial species are present in a sample and how evenly distributed they are. Higher diversity is often linked with resilience, but it's just one way to measure the health of your gut microbiome.
4) Should I take olive oil supplements?
This study examined dietary intake, not supplements. For most people, using olive oil in meals is the most practical approach.
5) How much olive oil should I have per day?
This study doesn’t establish an optimal “dose.” Instead, focus on swapping some lower-quality fats for higher-quality fats (like olive oil) within an overall balanced diet, and use extra-virgin/virgin when possible.
