A Review of Dr. Michael Greger’s Work on Olive Oil.
Within the plant-based world there is a school of thought that cautions against the consumption of olive oil. It is based on literature that was curated and promulgated by the renowned author and physician, Dr. Michael Greger.
Dr. Greger’s work stands in sharp contrast to a large body of science pointing to the opposite: That olive oil is actually very beneficial.
For us here at Plantraw®, Dr. Greger’s work wasn’t just a scholarly conundrum; it was a serious issue. We are committed to producing the very best snacks. One of our most popular products, the Tomato-Onion Chips, is made with extra virgin olive oil, an ingredient that is important both to the chips’ excellent mouthfeel and to their nutritional profile. If Dr. Gregor were correct, we would need to remove it.
We decided to look into Dr. Greger’s work. Following are our findings.
In this review we will refer to both olive oil and extra virgin olive oil simply as, “olive oil,” since this dichotomy is not relevant to our discussion. In each of the studies we cite it will be clear which oil type was examined.
On his website, Dr. Greger dedicates a page to olive oil. The first link on that page is to a study by the University of Maryland, which, according to Dr. Greger, demonstrated that “Olive oil was found to have the same impairment to endothelial function as high-fat foods like sausage and egg breakfast sandwiches.”
We read that study. Indeed, in page II-37, in the analysis for a graph labeled, Figure 5, the authors state that “Olive oil was also found to have the same impairment to endothelial function as the rest of these high-fat meals.”
The very next sentence clarified that, “this impairment, however, was also totally eliminated when vitamins C and E were given. As with antioxidant vitamin supplementation, olive oil, eaten with vinegar on a salad, did not impair endothelial function.” (Emphasis added).
In other words, when consumed with a salad, as is chiefly the case, olive oil is not harmful at all.
But Dr. Greger failed to mention this.
The second link on that page is to a video that was viewed more than 300,000 times on YouTube. It is packed with studies that Dr. Greger selected. In this video, Dr. Greger admits that studies show that olive oil is beneficial. But he claims that those studies measured ischemic reactive hyperemia (a temporary increase in blood flow), which is not a conclusive index of endothelial function.
But that is not true. In the studies that Dr. Greger presented, researchers analyzed a lot more than ischemic reactive hyperemia; they looked at multiple parameters.
In the second study researchers looked at “systolic and diastolic BP, serum or plasma biomarkers of endothelial function, oxidative stress, and inflammation, and ischemia-induced hyperemia in the forearm were measured.”
All these markers were measured in addition to Ischemic reactive hyperemia (IRH).
The fourth study that Dr. Greger presented was not a study at all; it was a letter to the editor, and it had nothing to do with olive oil. The cardiologist who wrote it was merely concerned with the use of reactive hyperemia (the temporary increase in blood flow after a blood vessel’s constriction) as a marker for endothelial function. That’s all. In our view, it was wrongful and misleading of Dr. Greger to pick a sentence from that letter and present it as “evidence” that olive oil is somehow harmful.
Dr. Greger then pulled another sentence from that letter about “hundreds of studies…” which again had nothing to do with olive oil. It appears that the sole purpose of this citation was to beef up nonexistent evidence.
After that, Dr. Greger presented the results of a study, from which he extracted one line purporting to show the “adverse effects” of olive oil. In fact, that study and those results showed the opposite: “In hypercholesterolemic men, diets low in fat (especially saturated fat) and diets rich in monounsaturated fats improve endothelial function.” Olive oil is rich in monounsaturated fats. Endothelial function is considered a marker of cardiac health. So, in fact, the study concluded that olive oil improved heart health in men with high cholesterol—the opposite of what Dr. Greger was claiming.
The next study concluded that some, but not all, the compounds in olive oil “decrease inflammatory mediator production”. Not every single molecule produced healthful effects, but those compounds that did, may “contribute to the antiatherogenic properties ascribed to extra virgin olive oil.” Again, the conclusion was that olive oil was a good thing. Still, Dr. Greger presented this study too as evidence that it was not.
Then Dr. Greger cited the “largest prospective study ever to assess the relationship between olive oil consumption and cardiac events like heart attacks.” Dr. Greger claimed that neither virgin olive oil nor olive oil “was found to significantly reduce heart attack rates after controlling for healthy dietary behaviors like vegetable intake, which tends to go hand-in-hand with olive oil intake.”
But that is not true. “Not adjusting for dietary factors may have led to an overestimation of the association” [emphasis added], but the association was very much there. As the authors concluded, “The present results are supported by strong mechanistic evidence and results from experimental studies show that consuming olive oil improves important CHD [Coronary Heart Disease] risk factors.”
Moreover, the authors cite other studies that have shown that “extra virgin olive oil benefits blood pressure, glycemic control in diabetics, endothelial function, oxidative stress, lipid profiles (decreasing TAG, increasing HDL- and lowering total and LDL-cholesterol) and reduces susceptibility of LDL to oxidation and concentrations of inflammatory markers such as C-reactive protein and IL-6. In addition, the olive oil-rich diet was effective in the prevention of diabetes, the metabolic syndrome and weight gain.”
Dr. Greger omits all this evidence. It negates the entire thrust of his argument.
A study later concluded that a meal rich in monounsaturated fatty acids (which compose 75% of olive oil) “does not impair endothelial function in subjects with type 2 diabetes.” Dr. Greger describes this as “more of a neutral effect, compared to butter.” But olive oil doesn’t have a neutral effect at all. A large body of science has shown that its polyphenols positively exert multiple health benefits.
The following study truly purported to call the health benefits of olive oil into question. In that study, the subjects were fed bread together with olive oil. In our view, this confounding factor vitiates the results. If you study oil, use oil, not oil plus other factors which may throw off the effects you are measuring.
Then Dr. Greger cited a study that showed that dietary antioxidants were beneficial. He proceeded to hypothesize, without any scientific evidence whatsoever, that perhaps the Mediterranean diet is healthy “despite” the olive oil component, and not “because” of it. In doing so, Dr. Greger completely ignores the 800LB body of scientific literature in the room that has shown that olive oil in and of itself is very good for human health.
In conclusion, it appears that Dr. Greger methodically extracted bits of sentences from various studies in an attempt to taint olive oil as harmful. Our investigation, however, reveals that those studies (and many others) demonstrated the opposite: Olive oil is beneficial for human health, and it is so in multiple ways.
Dr. Greger enjoys a broad following—readers and viewers who may further influence others. Therefore, his faulty conclusions about olive oil may have led a lot of people to omit it from their diet. The potential harm is so wide that we felt compelled to publish our findings.
 Vogel, R A. “Brachial artery ultrasound: a noninvasive tool in the assessment of triglyceride-rich lipoproteins.” Clinical cardiology vol. 22,6 Suppl (1999): II34-9. doi:10.1002/clc.4960221407
 Fuentes, F et al. “Chronic effects of a high-fat diet enriched with virgin olive oil and a low-fat diet enriched with alpha-linolenic acid on postprandial endothelial function in healthy men.” The British journal of nutrition vol. 100,1 (2008): 159-65. doi:10.1017/S0007114508888708
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 The writer, Tommaso Gori, MD, PhD, was secondarily concerned with the interchangeable use of the terms “endothelial” and “microvascular”, which he cautioned against.
 Fuentes, F et al. “Mediterranean and low-fat diets improve endothelial function in hypercholesterolemic men.” Annals of internal medicine vol. 134,12 (2001): 1115-9. doi:10.7326/0003-4819-134-12-200106190-00011
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 Tentolouris, Nicholas et al. “Differential effects of two isoenergetic meals rich in saturated or monounsaturated fat on endothelial function in subjects with type 2 diabetes.” Diabetes care vol. 31,12 (2008): 2276-8. doi:10.2337/dc08-0924
 Vogel, R A et al. “The postprandial effect of components of the Mediterranean diet on endothelial function.” Journal of the American College of Cardiology vol. 36,5 (2000): 1455-60. doi:10.1016/s0735-1097(00)00896-2
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 If we are successful in spreading the word, we expect the demand for olive oil to increase, making it more expensive, thus adversely affecting our profitability. But then, the whole point of starting this business to begin with was to improve people’s health.