The Cooking Oil That Cut Diabetes Risk by 40 Percent in a Major Trial

Type 2 diabetes does not arrive overnight. It builds slowly, over years, as the body loses its ability to manage blood sugar. Most of the risk factors are things people cannot control. The food they cook with every day is one they can.

A subgroup analysis of the PREDIMED trial, one of the largest and most rigorous nutrition studies ever run, tracked over 3,500 people for more than four years. Among those who did not have diabetes at the start, the group eating a Mediterranean diet with extra virgin olive oil developed type 2 diabetes at a rate roughly 40 percent lower than the control group. The full analysis is published in the Annals of Internal Medicine. This post explains what the trial actually tested, what the control group ate, why extra virgin olive oil specifically appears to matter, and what the evidence does not claim.

At a Glance: What the Research Shows •  3,541 adults without diabetes, followed for a median of 4.1 years •  EVOO group: 80 new diabetes cases. Control group: 101 new diabetes cases •  Roughly 40% lower relative risk of developing type 2 diabetes in the olive oil group •  No calorie restriction involved — the benefit came from a change in diet quality, not eating less •  The control group was advised to follow a low-fat diet and received small non-food gifts; they did not receive supplemental olive oil •  A 2025 meta-analysis of 10 studies covering 50,000+ people confirmed a 13% lower diabetes risk with higher olive oil intake •  10 to 20 grams per day, about one tablespoon, identified as the meaningful dose range

What the PREDIMED Trial Actually Tested

PREDIMED stands for Prevención con Dieta Mediterránea, a large Spanish randomized controlled trial that ran from 2003 to 2010. It enrolled 7,447 adults aged 55 to 80 who were at high risk for cardiovascular disease but did not yet have it. 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 follow a low-fat diet.

The control group is worth understanding clearly. They were not eating an extreme diet. They received standard advice to reduce fat across the board, and they were given small non-food gifts as a thank-you for participating. They were not given extra olive oil. Their actual diet, in practice, remained close to what most people in Spain were already eating.

The primary goal of PREDIMED was to study heart disease. But because participants were at elevated metabolic risk, researchers also tracked new cases of type 2 diabetes. The diabetes findings, published separately in the Annals of Internal Medicine, focused specifically on the 3,541 participants who did not have diabetes at enrollment.

Over 4.1 years, 273 new diabetes cases developed across all three groups. In the extra virgin olive oil group, there were 80. In the control group, there were 101. After adjusting for age, sex, weight, physical activity, and other factors, the extra virgin olive oil group had approximately 40 percent lower relative risk of developing type 2 diabetes. No one in the study was told to eat less or lose weight.

How Type 2 Diabetes Develops, and Where Diet Fits In

Type 2 diabetes is a condition where the body becomes progressively less responsive to insulin, the hormone that moves sugar from the bloodstream into cells. When cells stop responding normally, blood sugar stays elevated after meals. Over time, the pancreas works harder to compensate, eventually losing the ability to keep up. The result is chronically high blood sugar, which damages blood vessels, nerves, kidneys, and eyes.

The word to focus on is progressive. Type 2 diabetes does not appear suddenly. There is usually a window of years, sometimes a decade or more, where the body is moving in the wrong direction but has not yet crossed into a diagnosis. That window is where dietary choices carry the most leverage.

The central driver of that progression is insulin resistance: cells becoming less and less sensitive to insulin's signal. Chronic inflammation, excess visceral fat, and a diet high in refined carbohydrates and low-quality fats all accelerate insulin resistance. Swapping what you cook with every day is not a dramatic intervention, but done consistently over years, it changes the biochemical environment in which that progression happens.

For a broader look at how extra virgin olive oil interacts with the body's inflammatory markers, which are closely connected to insulin function: Is Extra Virgin Olive Oil Good for Inflammation?

The Two Reasons Olive Oil Affects Insulin Sensitivity

The reduction in diabetes risk seen in PREDIMED was not a statistical coincidence. Extra virgin olive oil contains two things that work on insulin function through separate pathways.

The first is oleic acid. Oleic acid is the dominant fat in olive oil, a monounsaturated fat with a different chemical structure from the saturated fats in butter and the refined polyunsaturated fats in most vegetable oils. Research has shown that oleic acid improves how efficiently cells respond to an insulin signal and reduces the oxidative stress inside cells that interferes with normal glucose metabolism. For a complete breakdown of what makes oleic acid biochemically distinct from other cooking fats: Oleic Acid Explained: The Monounsaturated Fat Behind Olive Oil's Benefits.

The second is polyphenols. These are the antioxidant compounds found in virgin olive oil that are almost absent from refined oils. Oleuropein influences glucose transport into cells and improves insulin receptor sensitivity. Hydroxytyrosol reduces oxidative stress at the cellular level. Both are present in meaningful amounts only in genuine extra virgin olive oil, and both appear to contribute to the metabolic effect seen in trials. For what polyphenols are and why their concentration varies so much between bottles: What Are Polyphenols in Olive Oil and Why Do They Matter. For a deeper look specifically at hydroxytyrosol: Hydroxytyrosol: The Antioxidant Researchers Are Calling Exceptional.

These two pathways work simultaneously. A high-quality extra virgin olive oil contains both a favorable fat profile and naturally occurring polyphenols, and research on metabolic outcomes consistently shows stronger effects with polyphenol-rich oils than with refined oils.

Ten Studies and 50,000 People Point the Same Direction

The PREDIMED diabetes finding does not stand alone. A 2025 dose-response meta-analysis published in the Journal of Health, Population and Nutrition pooled data from 10 studies covering more than 50,000 people and approximately 2,000 diabetes cases. Higher olive oil consumption was associated with 13 percent lower diabetes risk in cohort studies and 22 percent lower risk in randomized controlled trials. The analysis also identified a dose: roughly 10 to 20 grams per day, about one tablespoon, produced statistically significant risk reduction. Above 20 grams daily, the benefit plateaued.

When cohort studies and clinical trials point in the same direction across this many participants, the association is meaningful. It means the PREDIMED result was not an anomaly of one population or one research team.

This is also consistent with the broader cardiovascular evidence from PREDIMED. The same trial found significant reductions in heart attack, stroke, and cardiovascular death in the extra virgin olive oil group, published in the New England Journal of Medicine. The metabolic and cardiovascular findings appear to share the same underlying mechanism: better fat quality leading to less inflammation, less oxidative stress, and better vascular and insulin function. For a full look at the heart health data: Olive Oil and Heart Health: What 40 Years of Research Has Found.

Why the Oil Must Actually Contain Polyphenols

The PREDIMED trial used extra virgin olive oil. The 2025 meta-analysis shows the strongest effects in trials using higher-quality oils. This distinction matters because most of what is sold as olive oil does not deliver meaningful polyphenol content.

Refined olive oil, which includes bottles labeled as plain "olive oil" or "pure olive oil," has been processed to remove defects and extend shelf life. That process strips away most of the polyphenols. The fat profile remains similar to extra virgin, but the oleuropein and hydroxytyrosol are largely gone. What is left is a neutral cooking fat without meaningful antioxidant activity.

A scoping review published in Nutrients (2025) found that high-polyphenol extra virgin olive oil specifically showed improvements in fasting blood glucose, insulin sensitivity, and inflammatory markers in people with metabolic disease. Lower-polyphenol oils did not produce the same results. The polyphenols are not a bonus feature on top of a healthy fat. They appear to be a primary driver of the metabolic benefit.

The challenge is that polyphenol content is not printed on olive oil labels. A bottle can say extra virgin and still contain very few polyphenols if the olives were processed slowly, stored poorly, or bottled in clear glass and left sitting on a shelf under fluorescent light. Polyphenol levels are set before the oil reaches you. For why pressing speed is the biggest single determinant of what ends up in the bottle: Why Olive Oil Pressed Within Hours Is Superior. For what the extra virgin label actually guarantees and what it does not: Why Most Grocery Store Olive Oil Fails the Extra Virgin Standard.

What This Research Does Not Prove

The PREDIMED diabetes result is strong, but it comes with genuine limits that are worth understanding.

The diabetes finding was a subgroup analysis, not the primary endpoint of the trial. PREDIMED was designed to study cardiovascular disease. The diabetes outcome was tracked because participants were at metabolic risk, but the trial was not specifically powered or designed to answer the diabetes question. A dedicated randomized controlled trial focused on diabetes prevention would carry more definitive weight.

The 3,541 participants in this subgroup were older Spanish adults, aged 55 to 80, at high cardiovascular risk. They already consumed olive oil regularly as part of their cultural diet. Whether the same magnitude of effect would appear in younger people, or people whose baseline diets include very little olive oil to begin with, is not established by this trial alone.

The control group was advised to follow a low-fat diet, but in practice maintaining a genuinely low-fat diet is difficult. Compliance in the control group was imperfect. Some researchers have pointed out that this may have compressed the observed difference between groups. Whether the true benefit of extra virgin olive oil versus a realistic Western diet is larger or smaller than 40 percent remains an open question.

None of these limitations reverse the direction of the evidence. Multiple studies point toward a real association between extra virgin olive oil consumption and lower diabetes risk. The size of the benefit and how well it translates across different populations are still being established.

How to Use This Information Day to Day

Type 2 diabetes affects more than 500 million people worldwide, and rates continue to rise. Most of the risk comes from lifestyle factors that accumulate slowly over years. The cooking fat used at nearly every meal is one of those factors.

The research does not suggest that olive oil is a standalone solution. Even high-quality extra virgin olive oil is unlikely to offset a diet that otherwise works against metabolic health or the factors that contribute to insulin resistance. What the evidence does support is making genuine, high-quality extra virgin olive oil a consistent primary cooking fat within an overall dietary pattern that supports metabolic health.

The dose identified in the 2025 meta-analysis, about one tablespoon per day, is practical rather than medicinal. Most people who cook regularly with olive oil as their main fat reach this amount without thinking about it. For how this fits into weight and metabolic management more broadly: Can Olive Oil Help With Weight Management: The Mediterranean Diet Data.

Oil quality is the variable most people underestimate. A tablespoon of refined olive oil does not deliver the polyphenol load that drove the metabolic improvements in the research. If the goal is the benefit the science points to, the oil in the bottle actually has to contain polyphenols.

The most reliable way to know whether your oil still has polyphenols is to taste it. Fresh high-polyphenol extra virgin olive oil leaves a peppery sting at the back of your throat. That sensation is oleocanthal. No pepper means the polyphenols are largely gone. For how heat and storage affect what is left in the bottle after you bring it home: Does Heating Olive Oil Destroy Its Polyphenols and How to Store Olive Oil to Maximize Freshness and Polyphenol Retention.

What Makes Four Hour Olive Oil Different Polyphenol content is determined long before the oil reaches the bottle. It starts the moment an olive is picked. Four Hour Olive Oil presses Ayvalik olives within 4 hours of harvest. That window preserves the polyphenol levels that begin degrading with every hour of delay. USDA Organic certified. Single-origin. Bottled in Italian dark glass to protect polyphenols from light degradation after pressing. The polyphenols in your oil are not a marketing claim. They are what the research is pointing to. Shop Ultra Premium   |   Shop Premium   |   Shop Duo

Frequently Asked Questions

What did the PREDIMED trial actually find about diabetes?

3,541 adults without diabetes were followed for a median of 4.1 years. Those eating a Mediterranean diet with extra virgin olive oil developed type 2 diabetes at roughly 40 percent lower rates than the control group. There were 80 new diabetes cases in the olive oil group versus 101 in the control group. No calorie restriction was required. The benefit appeared to come from a change in diet quality and fat source.

What was the control group eating?

The control group was advised to follow a low-fat diet. They received standard dietary counseling and small non-food gifts for participation. They were not given extra olive oil. In practice, their diet remained close to what most people in Spain were already eating, which is why researchers describe it as a realistic comparison rather than an extreme baseline.

What is type 2 diabetes and why does diet affect it?

Type 2 diabetes is a condition where the body becomes progressively less able to respond to insulin, the hormone that manages blood sugar. As insulin sensitivity declines, blood sugar stays elevated after meals. This process builds over years. Diet matters because the fats you eat, the inflammation in your body, and your weight all directly influence how well insulin works during that long window before a diagnosis.

Does olive oil lower blood sugar directly?

Short-term trials measuring blood glucose and HbA1c after weeks of olive oil supplementation have produced mixed results. The stronger evidence is for long-term risk reduction: consistent extra virgin olive oil use over years appears to slow the progression toward insulin resistance and diabetes, rather than producing an immediate drop in blood sugar numbers. For a detailed look at the blood sugar research: Olive Oil and Diabetes: How EVOO Affects Blood Sugar and Insulin Sensitivity.

How much olive oil is needed to see a benefit?

The 2025 meta-analysis identified 10 to 20 grams per day, roughly one tablespoon, as the range where statistically significant diabetes risk reduction appeared in the data. Above 20 grams daily, the benefit plateaued. PREDIMED participants used olive oil as their primary cooking fat throughout the day, which likely corresponds to this range in practice.

Does it have to be extra virgin olive oil, or does regular olive oil work?

The research consistently uses extra virgin olive oil rather than refined olive oil. The polyphenols in extra virgin olive oil, including oleuropein and hydroxytyrosol, appear to drive a significant part of the metabolic benefit. Refined olive oil has a similar fat profile but very little polyphenol content after processing. The PREDIMED trial used extra virgin olive oil, and the research on high-polyphenol oils shows the clearest metabolic effects.

Why does polyphenol content vary so much between bottles?

Polyphenols begin degrading the moment an olive is picked. Every hour between harvest and pressing is an hour of loss. Producers who press quickly preserve more polyphenols than those who stockpile olives for a day or more before milling. After bottling, light and oxygen continue to degrade polyphenols. Dark glass slows light degradation significantly. A clear glass bottle sitting under grocery store lighting degrades the oil continuously from the day it was bottled. None of this is visible on the label.

Can I tell if my olive oil still has polyphenols?

The most reliable sensory signal is a peppery sting at the back of your throat when you taste the oil plain. That sensation comes from oleocanthal, one of the main polyphenols in fresh extra virgin olive oil. No pepper means the polyphenols are largely gone. A bitter note on the tongue signals oleuropein. Oil that tastes flat, greasy, or neutral has lost most of what makes it valuable from a health standpoint. For how heat and storage affect polyphenol levels after you bring the bottle home: How to Store Olive Oil to Maximize Freshness and Polyphenol Retention.

Is this relevant if I already have type 2 diabetes?

The PREDIMED diabetes analysis focused on prevention in people who did not have diabetes at the start. For people already managing type 2 diabetes, the evidence on olive oil and blood sugar control exists but is more mixed. Some trials show modest improvements in fasting glucose and HbA1c with consistent extra virgin olive oil consumption. Others show non-significant effects. If you have type 2 diabetes, speak with your doctor before making significant dietary changes. The research in this post should not be read as a substitute for medical management.

Is the 40 percent figure a relative or absolute risk reduction?

It is a relative risk reduction. The absolute numbers were 80 new diabetes cases in the olive oil group versus 101 in the control group, out of 3,541 people over 4.1 years. The relative risk reduction of roughly 40 percent describes the comparison between those two rates. Absolute risk reduction in both groups was small in percentage terms, as you would expect from a general population followed over four years. The relative figure is not misleading, but understanding both numbers gives a more complete picture.

Is the PREDIMED trial definitive proof that olive oil prevents diabetes?

No single study is definitive proof. The PREDIMED diabetes result came from a subgroup analysis of a trial designed primarily to study heart disease. The participants were older Spanish adults at high cardiovascular risk who already consumed olive oil regularly, which limits how directly the findings translate to other populations. What makes the evidence worth taking seriously is that multiple independent studies, using different designs and populations, consistently point in the same direction. The direction is clear. The exact size of the benefit across all populations is still being established.

Does cooking with olive oil reduce the polyphenol benefit?

Moderate cooking temperatures, such as a typical stovetop sauté, degrade some polyphenols but do not eliminate them. Using extra virgin olive oil raw, drizzled on finished dishes or salads, preserves the most. Extended high-heat frying degrades polyphenols more significantly. Most Mediterranean cooking uses olive oil across both applications: as a cooking fat for everyday meals and as a finishing oil. For a full breakdown of what happens to polyphenols at different temperatures: Does Heating Olive Oil Destroy Its Polyphenols.

References and Sources

All studies are linked directly. Editorial framing is original to Four Hour Olive Oil.

[1] Salas-Salvado J, et al. Prevention of diabetes with Mediterranean diets: a subgroup analysis of a randomized trial. Annals of Internal Medicine (2014) 160:1-10. View study [2] Estruch R, et al. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. New England Journal of Medicine (2018) 378:e34. View study [3] Du Y, Zhou H. Effect of olive oil consumption on diabetes risk: a dose-response meta-analysis. Journal of Health, Population and Nutrition (2025) 44:135. View study [4] Vitale M, et al. High Polyphenol Extra Virgin Olive Oil and Metabolically Unhealthy Obesity: A Scoping Review of Preclinical Data and Clinical Trials. Nutrients (2025). View study

The information in this article is based on peer-reviewed research and is provided for educational purposes only. It is not intended as medical advice. Please consult a qualified healthcare professional before making changes to your diet or supplement regimen.