In the past 25 years, olive oil has taken on the status of a health food, initially among those trying to improve their cholesterol levels and protect their heart, but then also among people who were just generally health-conscious. Yes, olive oil, like all plant oils, is 100 percent fat—but supposedly a “good fat.” A large part of its attraction has been due to accumulating research about the health benefits of the Mediterranean diet, of which olive oil is a key element. Smart marketing has played a big role, too. The olive oil industry has sponsored lots of research and deftly promoted its product to consumers as well as nutritional experts.
Olive oil is sometimes promoted because it is high in monounsaturated fats, but so are canola and “high-oleic” sunflower and safflower oils (see The Skinny on Fats below, about different types of fats). And the fact is that corn, soybean, and other polyunsaturated oils are better than olive oil at lowering LDL (“bad”) cholesterol and thus reducing coronary risk. Still, for many health-conscious people, none of these oils compare to olive. For them, and for some experts, there are other things about olive oil besides its effect on blood cholesterol that make it superior—notably the polyphenol compounds it contains. Let’s take a closer look at the olive oil story.
Why olive oil became hot: observational studies
Olive oil has been the basic edible oil in regions around the Mediterranean since the Bronze Age. Three thousand years or so later, in 1958, the famous Seven Countries Study gave olive oil a big boost. It observed that men who had low intakes of saturated fats had the lowest blood cholesterol and the lowest rates of heart disease (heart studies didn’t include women back then). Strikingly, the very lowest rates were found in Greece, on the isle of Crete, where the diet was relatively high in unsaturated fat, which came primarily from olive oil.
Keep in mind, however, that these Greeks did lots of heart-healthy things— consuming mostly plant-based foods, moderate amounts of wine and fish, and very little meat, as well as doing hard physical work—so it’s difficult to know how important olive oil was. Note, too, that the Japanese, who consumed no olive oil, were also found to have a very low rate of heart disease.
Many subsequent observational studies also linked the traditional diets of various Mediterranean countries, all of which use olive oil as the primary fat, to cardiovascular and other benefits, including reduced mortality rates.
An important Spanish dietary trial called PREDIMED (Prevención con Dieta Mediterránea) was designed to determine the long-term effects of versions of the Mediterranean diet in people at high cardiovascular risk (see Mediterranean Diet Best for Heart?). Participants were divided into three groups: Mediterranean diet plus additional olive oil; Mediterranean diet plus nuts (one ounce a day); or a lower-fat diet (the control group, still basically Mediterranean).
The first study to come out of the PREDIMED trial was published in 2013 and showed that after five years both the olive oil and nut groups had fewer cardiovascular events than the control group, especially fewer strokes in the nut group. More recently, follow-up PREDIMED studies have linked the Mediterranean diet enriched with olive oil to a variety of benefits, including a reduced risk of cognitive decline, breast cancer, and osteoporotic fractures.
It’s uncertain, however, how big a role olive oil played in PREDIMED, since the control group consumed nearly as much (averaging three tablespoons a day) as the olive oil group (four tablespoons). It’s also not known how other oils might have compared.
Virgin vs. Extra Virgin Olive Oil
Why are some olive oils labeled virgin or extra virgin? The difference is in the processing, which yields oils of different acidity and hence taste.
So which oil is best for improving blood cholesterol levels?
Much research, including animal studies and relatively short-term clinical trials, has focused on the relationship between dietary fats and blood cholesterol. It’s clear that foods high in polyunsaturated fats lower LDL cholesterol when they replace foods high in saturated fats (such as butter) or refined grain products; monounsaturated fats, less so. That’s why the American Heart Association emphasizes polyunsaturated fats in a heart-healthy diet, though it also recommends monounsaturated fats. So if your chief concern is to improve your cholesterol levels, you have nothing to gain by choosing olive oil or another monounsaturated oil over corn, soybean, or other polyunsaturated oils.
What about HDL (“good”) cholesterol? It used to be thought that polyunsaturated fats also lower HDL, while monounsaturated fats do not, or that they even raise it. But most research has found that all unsaturated oils, in the amounts commonly consumed, have only a small effect on HDL levels, depending in part on what foods they replace in the diet. In any case, some recent studies have led many researchers to de-emphasize the importance of HDL as an independent factor in heart disease (see Good Cholesterol Not So Good?).
The Skinny on Fats
All plant oils are nearly pure fat and, like all fats, are combinations of saturated, monounsaturated, and polyunsaturated fatty acids. Here are definitions for those fatty acids as well as for trans fats.
Other potential benefits
• Olives contain polyphenols, a large group of compounds that are found in many plant-derived foods and that have been linked to an array of potential benefits. The less processed olive oil is, the more polyphenols it retains. Extra virgin olive oil is least processed (see box below on left), and most studies, including PREDIMED, have used it. The European Food Safety Authority allows bottlers of olive oil with high polyphenol content to make a heart health claim. Heating olive oil destroys some of these compounds. Keep in mind that olive oil is hardly unique—polyphenol intake from many foods (notably chocolate, tea, fruits, and vegetables) is associated with a wide range of health benefits.
• Aside from its effect on cholesterol levels, olive oil may reduce cardiovascular risk in other ways. For instance, some research suggests that it helps lower blood pressure (at least a little) and inflammation, as well as reduce the tendency of blood to clot, which may lower the risk of a heart attack or stroke. Indeed, an observational study in Neurology in 2011 found that older French people who consumed the most olive oil had a dramatically lower risk of stroke than those who seldom consumed it. And in 2015 still another PREDIMED study found that participants in the olive oil or nut groups who consumed the most polyphenols had significantly lower blood pressure than the control group. In addition, the most recent PREDIMED study, published in Circulation in 2017, found that while the diet with extra olive oil did not increase HDL levels, it modestly improved HDL’s efflux capacity—that is, its ability to remove cholesterol from plaque in arteries so it can be eliminated from the body—and also enhanced HDL’s anti-inflammatory and antioxidant capacity
• Monounsaturated oils may help people with type 2 diabetes or prediabetes control their blood sugar. That’s one reason why the American Diabetes Association advises a monounsaturated-fat-rich Mediterranean-style diet as one of its recommended eating patterns. A 2009 study in Diabetes Care, for instance, compared a high-monounsaturated-fat diet (such as Mediterranean) to a standard heart-healthy, lower-fat diet in people with diabetes and found that, over the course of a year, they were equally good in improving blood sugar control, body weight, blood cholesterol, and other cardiovascular risk factors. In addition, olive oil consumption is associated with a modestly reduced risk of developing diabetes, according to a 2015 analysis from the Nurses’ Health Study.
• Oils high in monounsaturated fats are less susceptible to oxidation during cooking than polyunsaturated oils. Oxidation promotes the formation of free radicals and other potentially harmful compounds. This is primarily a problem when oil is heated to very high temperatures and for prolonged periods—as in some restaurants. Reheating oil, as for repeatedly making French fries, is especially damaging.
There is no perfect oil for every purpose. Flavor is a big factor, but it is largely destroyed by cooking. Another factor is the oil’s smoke point—the temperature at which it will start to break down and smoke. For frying or stir-frying, choose an oil with a high smoke point. The more refined the oil, the higher its smoke point. So if you want to use olive oil for high-heat cooking, opt for a more refined (and cheaper) “light” product. For extra flavor in salad dressings, experiment with specialty oils like avocado, almond, grapeseed, dark sesame, hazelnut, and walnut oil—or drizzle them on food after cooking.
Choose olive oil if you like it, not because you think it’s a health food. Canola, avocado, peanut, high-oleic safflower, and high-oleic sunflower oil are also rich in monounsaturated fat. Corn, regular sunflower, peanut, walnut, and other polyunsaturated oils are good choices, too, particularly for their LDL-lowering ability when they replace foods high in saturated fat, such as butter. Though extra virgin olive oil is the best source of polyphenols, many oils are also likely to contain potentially beneficial compounds, albeit in small amounts per typical serving, especially compared to fruits, vegetables, and nuts. The exact amounts depend on the source of the oils and how processed they are.
Don’t forget that all plant oils contain about 120 calories per tablespoon. If you simply add them to your diet, you’re likely to gain weight. The trick is to use them to replace other high-calorie foods.
Finally, keep in mind that there have been numerous reports of olive oil being diluted with cheaper, highly refined oils such as soybean or corn, and of more-processed olive oil being labeled “extra virgin.” For more about olive oil fraud and how to make the best choices, see Olive Oil: Desperately Seeking Quality.
Also see Canola Oil Myths and Truths.
Published September 04, 2017