Chapter 58
Olive Oil
Scientists developed a variety of scoring systems because they wanted to know whether people who eat a Mediterranean diet actually fare better. You get more points the more plant foods you consume; meat and dairy products mean points off. So it is not surprising that participants with higher scores have a lower risk of heart disease, cancer, and all-cause mortality. Compared with the standard American diet, the Mediterranean diet is more protective—without a doubt—however, any way of eating that includes more whole plant foods and little animal fat offers protection against many of our leading causes of death.
Dozens of prospective cohort studies show that people are less likely to succumb to premature death when they adhere more strictly to a Mediterranean-style diet. There can be a two-year difference between the age at death of those who ate the least Mediterranean and those who ate the most Mediterranean. The Mediterranean diet is also associated with healthy aging and a lower risk of frailty. What is the special protective function of this way of eating?
A meta-analysis of studies on the most protective components of the Mediterranean diet found that its mortality benefit lies in increased consumption of fruits and vegetables and reduced meat consumption. By contrast, fish, the only animal product in the Mediterranean diet, did not appear to play a role.
Criticism of Dr. Keys has recently become fashionable among “bloggers, commercial authors, or journalists in search of sensational topics or financial gain,” but scientifically speaking it is clear that such smears “are based either on incompetent research or sheer dishonesty bordering on scientific fraud.” Even the unsurpassed scientist Dr. Keys answered, on his 100th birthday, when asked whether he thought his diet contributed to his long life: “Very likely, but unproven.”
Dr. Stamler said the same thing about the Mediterranean diet on his 100th birthday. Even after that, he continued his pioneering work. He died on January 26, 2022, at the age of 102 years.
Olive Oil
In the Mediterranean region, olive oil is typically used with vegetables and salads, beans, and other legumes, so its intake may be an indicator of a more traditional, healthier diet. To be able to look at its effect in isolation, one would have to study olive oil consumption in a country outside the Mediterranean region. Harvard researchers took on this task and dug through decades of data from nearly 100 000 women and men in the Nurses’ Health Study and the subsequent Health Professionals Follow-up Study. They found that a teaspoon of olive oil instead of a teaspoon of butter, mayonnaise, margarine, or animal fat daily can, as expected, reduce the risk of heart disease by 5 to 7 percent. So olive oil is better than butterfat, but no significant difference was found between olive oil and other oils.
What about the study that is often promoted by proponents of a low-fat diet, which states that not only saturated fatty acids but also monounsaturated and polyunsaturated fats are responsible for atherosclerotic tears in the coronary arteries? I explain the crucial flaw in the argument in see.nf/mediterranean. In fact, olive oil is better for our LDL cholesterol level or arterial function than butter, although olive oil—even extra virgin—can impair arterial function, and to a similar degree as fast food and cheesecake.
Palm, soybean, and sunflower oils can also impair our arteries’ ability to relax and dilate normally. That does not happen when we consume Green Light sources of fat, such as nuts or avocados. (In How Not To Die I defined Green Light foods as foods of plant origin to which nothing bad has been added and nothing good has been taken away.) A diet consisting of whole plant foods may even be able to offset the negative effects of oil. If, for example, you consume this extra virgin olive oil in a balsamic vinaigrette as a dressing on a salad, that neutralizes the negative effect on the arteries. Unfortunately, the source of olive oil—the olives—contains too much salt because of preservation in brine, so you should not eat them regularly. Just twelve large olives can be enough to cover almost half of the recommended daily sodium.
How do we find out whether important sources of plant fats such as olive oil or nuts help us or harm us when it gets serious—when it is about diagnosed diseases, for example? Ideally, we would need to conduct a randomized trial running for several years with thousands of participants, in which one third get more nuts, one third get more olive oil, and the last third continue eating as usual; then we could see who does better. And that is exactly what researchers did.
PREDIMED
In the PREDIMED study (from the Spanish PREvención con DIeta MEDiterránea, “Prevention with a Mediterranean Diet”), the impressive number of 7447 participants at high risk of heart attack were randomized into three groups. For all the nitty-gritty, see see.nf/predimed, but basically the participants—contrary to the researchers’ original intention—were assigned for four years to (1) switch from about three tablespoons of semi-virgin olive oil daily to four tablespoons of extra virgin olive oil, (2) switch from about 15 grams of nuts daily to 30 grams, or (3) more or less continue eating as they had up to then. The results were published in the New England Journal of Medicine.
Wasn’t PREDIMED retracted?
The PREDIMED study is one of the most influential randomized nutrition studies of all time; nevertheless, the original publication was retracted in 2018 because there had been irregularities in randomization at two of the eleven data-collection sites. Members of a household were invited to participate and assigned to the same diet. That makes sense, because that way you do not have to assign different diets to members of the same household, but the core of randomized controlled trials is to randomize the assignment. Fortunately, this problem affected only about 6 percent of the participants. And after correction, reanalysis, and republication of the data, the original results and conclusions remained the same.
What happened over time to the amount of buildup in the arteries of the PREDIMED participants? In the control group with an unchanged diet, there was a significant worsening in carotid artery thickening with plaque; in the olive oil group, no notable changes; but the participants in the group with the additional nuts showed a significant reversal in thickening, and plaque formation came to a halt. The scientists concluded from this that nuts are not only a better source of fat than olive oil, but that beyond that they may “delay the progression of atherosclerosis, the harbinger of impending cardiovascular diseases” such as strokes. And that is exactly what seemed to happen. The participants who switched to extra virgin olive oil suffered about one third fewer strokes; those who supplemented their diet with nuts nearly cut their stroke risk in half, as it fell from about 6 to 3 percent for the next ten years. If nuts work just as well in the general population, more than 85 000 strokes a year could be prevented, in the United States alone. Imagine that: about ten fewer strokes every hour, simply by everyone eating five more almonds, walnuts, and hazelnuts every day.
There were no significant differences among the three groups in terms of consumption of meat and dairy products and therefore no significant differences in saturated fat or cholesterol intake, so, as expected, there were also no significant differences in the participants’ cholesterol levels or in the number of subsequent heart attacks. In the roughly five years the study ran, there were 37 heart attacks in the olive oil group, 31 in the nut group, and 38 in the group that kept eating normally. Similarly, there were no significant differences among the groups in deaths due to heart attack, stroke, or any other disease. However, markedly fewer participants in the olive oil group—and especially in the nut group—suffered strokes.