Just a few months ago, I was privileged to speak on a panel at the American College of Cardiology conference in Orlando, FL. My panel, devoted to the benefits of plant-based diets, included prominent champions of plant-exclusive (vegan) diets.
One of them, making the case for the diet he favors- plant exclusive, and without any added oil- espoused the view that olive oil is a cardiac toxin. He cited a study in which an acute dose of olive oil caused the same vascular impairment- called endothelial dysfunction- as several other oils.
Yes, there is indeed such a study, from ten years ago, in ten men. Does that establish the fundamental truth about olive oil and cardiovascular health? With all due respect and affection to my colleague, it most certainly does not. In the context of a fair and impartial hearing, and a full understanding of the topic, the study leads only to a question, not an answer: which olive oil?
This past week, Yale University hosted the Mediterranean Diet Roundtable conference, where I was privileged to serve as MC for the sessions devoted to nutrition science. Among the presentations were two by world leading experts in the bioactive components of olive oil, Eleni Melliou, PhD, and Prokopios Magiatis, PhD, both from the University of Athens.
Among those many compounds is oleocanthal, and we may focus on just that one for our purposes today. Oleocanthal is a polyphenol and potent antioxidant found in olives. It is established to inhibit COX1 and COX2 enzymes. What does that mean? The first, inhibition of COX1, is what ibuprofen does. The second, inhibition of COX2, is what Celebrex does. So, oleocanthal-rich olive oil (let’s call this “OROO”) has potent anti-inflammatory, and potentially analgesic (pain reducing) properties. What does the research show?
As presented by my colleagues from Athens, a study of OROO in 200 men in Spaindemonstrated a linear increase in protective HDL cholesterol, and a decline in LDL cholesterol. In a study of 24 women with hypertension, OROO was found to lower blood pressure, improve endothelial function (the exact opposite of the effect cited by my colleague in Orlando), and lower CRP, an important inflammatory marker. Multiple other studies cited by my Greek colleagues, and accessible here to those so motivated, replicated these effects.
OROO has been shown to inhibit platelet aggregation as well, the mechanism responsible for acute myocardial infarction. Like ibuprofen, aspirin inhibits COX1, so there is a clear case for the actions of compounds in olive oil to resemble effects seen with these drugs. Aspirin is used routinely as a cardioprotective agent because it inhibits platelet aggregation.
Oleocanthal derived from olive oil has been shown to induce the clearance of the plaquesassociated with Alzheimer’s disease from the brains of experimental animals. In another animal study, OROO potentiated the beneficial effect of the Alzheimer’s drug, donepezil. Results of a human trial, announced just last month, showed an improvement in Alzheimer’s symptoms, and delayed progression of the disease, with OROO.
Oleocanthal has also been shown to induce cancer cell death. In an on-going study of patients with chronic lymphocytic leukemia, OROO daily for 3 months significantly reduced the numbers of cancerous white blood cells relative to placebo.
There was more to these rather stunning presentations, but I trust that will suffice. Now, let’s make some sense of the jarring contrast between “olive oil is a toxin, and “olive oil can apparently fix everything.”
First and foremost, it depends on the olive oil. The active compounds in olive oil, like oleocanthal, are highly concentrated in the unripe olives used to make cold-pressed, extra virgin olive oil. They are almost completely absent from the ripe olives used to make the lesser varieties of olive oil that often populate the shelves of American supermarkets. To dismiss olive oil as toxic because of isolated data from what was no doubt very bad olive oil is rather like blaming Teslas for diesel exhaust from trucks because both are “motor vehicles.” Details matter.
Second, this is a precautionary tale about how readily science can be used to obscure rather than reveal the truth, even by those with good intentions. There is a study, somewhere, showing just about anything you care to find. Citing just the study that happens to support your view, without considering the weight of evidence, is called “cherry picking.” It is terribly common, understandably tempting, and horribly pernicious. I founded the True Health Initiative for just such reasons: to elevate the common understanding of diverse scientists from many countries over any one person's native preferences (including my own), and to help show that the fundamental truths of healthful diet and lifestyle are predicated on science, sense, and global consensus, aligned with the weight of evidence. They do not change every time a single study provokes hyperbolic headlines you happen to love, or hate.
So, yes, there is a study in ten people, using who-knows-what olive oil, showing one kind of adverse effect. To base a summary judgment on this is to ignore the details of the study itself, and dismiss the bulk of evidence on the same topic. I call upon my colleagues to resist this temptation, no matter how findings may align with native preferences, and I call upon you to beware the vulnerability of scientists to this temptation.
The above does not make the case that olive oil, or a Mediterranean diet, is required for good health. The fact that “A” is good tells us nothing about “B.” There may well be a “B,” or “C,” that is as good, or even better. But the above certainly does make the case that genuinely good olive oil has genuinely good health effects. No surprise, then, that of the world’s five Blue Zone populations, two have OROO-rich, Mediterranean diets. That, too, is evidence that matters.
I find the weight of evidence regarding extra virgin olive oil, OROO, and oleocanthal extremely compelling. I am fully persuaded that “good” olive oil is a signature contributor to the many benefits of one of the world’s truly great diets.
I am also persuaded, however, again based on the full weight of relevant evidence, that dietary patterns can be great with or without olive oil, whether high or low in total fat. No one food or nutrient accounts for the net effects of the overall diet.
I am fully persuaded that diets can be great with or without cherries, too. The one true toxin I see in the mix- corrosive to consensus, understanding, common ground, and common cause- is cherry-picked science.
David L. Katz, MD, MPH, FACPM, FACP, FACLM, is the Founding Director (1998) of Yale University’s Yale-Griffin Prevention Research Center, and current President of the American College of Lifestyle Medicine. He has published roughly 200 scientific articles and textbook chapters, and 15 books to date, including multiple editions of leading textbooks in both preventive medicine, and nutrition. He has made important contributions in the areas of lifestyle interventions for health promotion; nutrient profiling; behavior modification; holistic care; and evidence-based medicine. David earned his BA degree from Dartmouth College (1984); his MD from the Albert Einstein College of Medicine (1988); and his MPH from the Yale University School of Public Health (1993). He completed sequential residency training in Internal Medicine, and Preventive Medicine/Public Health. He is a two-time diplomate of the American Board of Internal Medicine, and a board-certified specialist in Preventive Medicine/Public Health. He has received two Honorary Doctorates.