Olive oil, specifically extra virgin olive oil used in place of refined carbohydrates and processed fats, is one of the better supported everyday food choices for heart health. But the headline evidence has a complicated history that almost nobody mentions. The big trial everyone cites, PREDIMED, was retracted in 2018 and then republished the same year (Estruch et al., New England Journal of Medicine) after the authors found problems with how some participants had been randomized. The reanalysis still reported a lower incidence of major cardiovascular events in the groups eating a Mediterranean diet supplemented with extra virgin olive oil or nuts. It just described the finding more carefully. That is the honest version, and it is still a good reason to keep a bottle of decent olive oil on your counter.
What did the PREDIMED trial actually find?
PREDIMED was a large Spanish trial in adults at high cardiovascular risk. Participants were assigned to one of three groups: a Mediterranean diet supplemented with extra virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control group advised to eat a lower fat diet. Researchers then tracked major cardiovascular events over several years.
The two Mediterranean diet groups had fewer of those events than the control group. That was the 2013 result, and it survived the 2018 reanalysis. What is worth understanding is what was being compared. This was not olive oil versus nothing. It was a whole pattern of eating, supported by free food and regular dietitian contact, versus general advice to eat less fat. Olive oil was part of the package, not the isolated active ingredient.
Why was the original paper retracted, and does that matter?
In 2018 the authors reported that some participants had not been individually randomized as described. At one site, participants were enrolled by clinic. In some cases household members of an enrolled participant were assigned to the same group rather than randomized separately. That breaks a core assumption of a randomized trial, so the journal retracted the 2013 paper and published a corrected version.
Here is the part that builds trust rather than destroying it. The authors reran the analysis excluding and adjusting for the affected participants, and the direction of the finding held. They also softened their language, moving away from claims about prevention toward describing a lower observed incidence of events. That is what good science correction looks like: the claim got smaller and more careful, not louder.
What it means for you: treat olive oil as a well supported association within a broader eating pattern, not as a pill that lowers your risk by a specific percentage. Anyone quoting you a precise number from a single trial is overselling it.
How does olive oil fit into insulin load?
Olive oil is essentially pure fat. It has no glycemic load of its own, so it does not directly drive a glucose spike the way bread, juice or a sweetened sauce does. In the Insulin Fix score, fat quality is one of the inputs, and extra virgin olive oil sits at the favourable end of it: minimally processed, rich in monounsaturated fat, and carrying the polyphenols that give good oil its peppery finish.
The bigger effect is usually indirect. Fat added to a meal tends to slow gastric emptying, which research suggests can blunt how fast glucose arrives in the bloodstream. And olive oil often earns its place by displacing something worse. A vinaigrette of olive oil and vinegar replaces a sweetened low fat dressing. Roasted vegetables in olive oil replace a side of white rice. Bread dipped in olive oil replaces bread with a processed spread. That swap is where most of the practical benefit lives.
What are the specific swaps worth making?
- Salad dressing: two parts extra virgin olive oil, one part vinegar, salt, mustard. Most bottled "light" dressings replace the fat with sugar or corn syrup.
- Bread: dip in olive oil with a little salt instead of using margarine or a processed spread.
- Vegetables: toss broccoli, cauliflower or green beans in olive oil and roast them. Fat makes vegetables something you actually want to eat, which matters more than any nutrient argument.
- Finishing oil: drizzle raw olive oil over soup, fish, eggs or beans at the table. Heat degrades polyphenols, so uncooked oil delivers more of what makes good oil good.
- Sauces: olive oil, lemon and herbs instead of a bottled sauce with sugar high in the ingredient list.
How do you buy olive oil that is worth the money?
Quality varies a lot, and price is not a reliable guide. A few things to look for:
- A harvest date on the bottle, not just a best before date. Olive oil is a fresh product and it fades with time.
- Dark glass or a tin. Light degrades oil. Clear plastic bottles on a bright shelf are a bad sign.
- A peppery, slightly bitter finish. That catch at the back of your throat comes from polyphenols. Bland oil is usually old or heavily refined.
- "Extra virgin" as the grade, ideally with a single country or region of origin rather than a blend of several.
Store it in a cupboard away from the stove, not next to it, and use an opened bottle within a couple of months. If you are buying a large tin for value, decant into a smaller bottle for daily use.
What should you not conclude from this evidence?
Three things worth being clear about. First, olive oil is not a supplement you add on top of an otherwise poor diet. In PREDIMED it came inside a whole pattern that also included vegetables, legumes, fish and nuts, with less red meat and fewer sweets. Second, no trial showed that pouring more olive oil into your day makes you healthier without limit. It was used as a replacement fat, not an addition. Third, a trial in high risk Spanish adults does not automatically transfer to everyone, and the 2018 correction is a reminder to hold single studies loosely.
What holds up is unglamorous and useful: real food, cooked at home, with good fat instead of processed fat and instead of refined carbohydrate. That is two of the seven hacks working together, healthy fats and real food, and olive oil is the easiest place to start.
Frequently asked questions
Is extra virgin olive oil worth the extra cost over regular olive oil? For raw and finishing uses, yes. Extra virgin is mechanically pressed and keeps the polyphenols that refined olive oil loses. Many people keep extra virgin for salads and drizzling and a cheaper oil for high heat cooking, which is a reasonable compromise.
Can you cook with extra virgin olive oil? Yes, for normal home cooking. Its stability is better than the smoke point number alone suggests, partly because of its antioxidant content. You will lose some polyphenols to heat, so if you are cooking a lot, keep a separate bottle for finishing raw.
Does olive oil raise blood sugar? On its own it contains no carbohydrate, so it does not directly raise glucose. Added to a mixed meal, fat tends to slow digestion, and research suggests that can moderate how quickly glucose rises. Individual responses vary, so if you use a glucose monitor, test your own meals.
Given the retraction, should I ignore PREDIMED? No, but hold it as one strong piece of a larger picture rather than proof. The corrected 2018 analysis still pointed the same direction, and it lines up with a lot of other work on Mediterranean style eating. Treat it as association within a pattern, not a guarantee about your individual risk.