Olive oil is often praised as the paragon of oils and an essential part of a healthy diet. Upon examination of the evidence however it becomes clear that eating olive oil is not the way to optimal health.
The Basics of Olive Oil
Olive oil is not a whole food. It is a processed, concentrated fat extract that retains little of the nutritional value of an olive, the source from which it comes. Olive oil is calorie-dense with one tablespoonful containing 120 calories (1). This means that olive oil contains about twice as many calories as the 64 calories found in a tablespoonful of pure refined sugar (2). Adding olive oil to any food significantly increases its calories and, because these calories are packed into such a small amount of oil, brings with it no feeling of fullness in the stomach to send the important message to the brain that enough calories have been eaten. In practical terms, adding olive oil can quickly ramp up your calorie consumption, contributing to weight gain and obesity.
What is the difference between regular olive oil and extra-virgin olive oil?
The difference in olive oil types comes from the processing they have experienced. Extra-virgin olive oil is obtained from the first physical cold crushing of the olive paste. Regular olive oil is processed with added heat and chemical solvents. Extra-virgin olive oil has a darker color, while regular olive oil is lighter and brighter. Extra-virgin olive oil is lowest in acid of the olive oil types and has a fresh, fruity flavour. In addition, extra-virgin olive oil contains fewer chemicals and free radicals along with higher levels of antioxidants. (3)
According to the USDA National Nutrient data base, 100 gm (3.5 ounces) of olive oil consists of the following components (4);
Almost 100 gm of fat approximately made up of…
14 gm (14%) saturated fat
73 gm (73%) monounsaturated fat
11 gm (11%) polyunsaturated fat (of which 0.8 gm is omega-3 fat and 9.8 gm is omega-6 fat)
14 mg Vitamin E
60 mcg Vitamin K
1 mg calcium
1 mg potassium
0.56 mg iron
Why is olive oil considered healthy?
There are two main reasons.
Firstly, compared to most other plant-sourced oils, olive oil contains relatively high amounts of oleic acid, a monounsaturated fatty acid.
Secondly, olives contain antioxidants in their pulp and oil.
The antioxidant content of olive oil
The most significant antioxidants in olive oil are polyphenols, plant sterols, and carotenoids. The actual antioxidant content of a specific olive oil depends on many factors – the variety of olive, the geographical area in which the olives are growing, the climate and the level of maturation at the time of harvesting. For example, olives grown in warmer climates are richer in phenols while over-ripe olives contain less. Additionally, the amount of antioxidants in the final oil depends greatly on the extraction process used (3).
Potential benefits of the antioxidants in olive oil
Polyphenols play a major role in the protective effects that plant foods in general have on health. Their effects include lowered blood pressure and cholesterol, prevention of plaque build-up in arteries, improved artery function, decreased inflammation and increased life span (5).
Plant sterols, when ingested in amounts of about 2 to 3 grams daily, can reduce LDL-cholesterol blood levels. They do this because their structure is similar to that of cholesterol allowing the absorption of plant sterols instead of LDL-cholesterol (6).
Carotenoids protect cells from the damaging effects of free radicals and support natural immunity against infections, especially viral infections. They are also associated with lower risk of some cancers and promote skin and eye health (7).
There is a hitch however in the perceived antioxidant component of olive oil. Olives do not contain a large amount of these healthy molecules compared to other whole fruits and vegetables. And so it follows that the oil squeezed from olives is not a rich source of phenols, plant sterols, or carotenoids either.
When analyzed, black and green olives rate as medium sources of antioxidants, containing far lower amounts than other plant foods such as berries including strawberries, blackberries and cranberries; and greens such as kale (8).
A 2004 study looked at the availability and activity in humans of the phenols present in extra-virgin olive oil. The study focused on the potential of olive oil phenols to prevent oxidation of LDL-cholesterol molecules since it is oxidized cholesterol that plays a prime role in the development of atherosclerosis and cardiovascular disease. Results showed that olive oil phenols are well-absorbed in humans, however, the antioxidant activity of these phenols was too low to inhibit the oxidation of LDL (9). In addition, intake of phenols from other foods is much higher. For instance, phenol blood levels after drinking tea are 25 times higher than those following extra-virgin olive oil ingestion (9).
Clinical trials have shown that daily consumption of 2 gm daily of plant sterols can lower serum LDL-cholesterol by 8% to 10% (10). The USDA Food Composition Database identifies 30 mg of plant sterols in each tablespoonful of olive oil. This would mean that a person would need to consume the huge amount of 66 tablespoonsful (over 4 cups) of olive oil every day to obtain enough plant sterols to significantly reduce their blood LDL-cholesterol levels through the ingestion of olive oil alone (11,12).
In contrast, a cup of uncooked kidney beans (about 2 cups once cooked) contains approximately 304 mg of plant sterols. Plant sterols are not degraded by cooking and in fact cooking beans will produce significantly higher values of free plant sterols than listed here (13,43).
Does olive oil protect from heart disease?
First of all, a little background information will help make this discussion easier to understand. Human blood vessels are lined with a single layer of cells called endothelial cells. These cells produce a gas called nitric oxide that keeps blood vessels healthy, allowing them to expand when increased blood flow is required and preventing platelets from sticking to blood vessel walls. When endothelial cell function is impaired, blood pressure rises and atherosclerosis, the build-up of plaques on the insides of blood vessels, begins to develop.
There is no shortage of evidence that olive oil is not protective for the cardiovascular system. Testing has shown that all oils, no matter their source, worsen the function of the endothelium so that blood vessels stiffen and will not dilate normally for a few hours after they have been consumed. Here are a few examples of this evidence.
In 1999 a review of previous studies showed that meals consisting of a hamburger and fries or a slice of cheesecake caused significant impairment to endothelial function (14).
In the year 2000 another study measured the change in blood flow through the brachial artery (the major blood vessel in the arm) after consuming five different fat-containing meals (15).
The meals all contained 900 calories and 50 grams of fat.
Meal 1: Extra-virgin olive oil with non-preservative-containing whole-grain bread
Meal 2: Canola oil with non-preservative-containing whole-grain bread
Meal 3: Canned red salmon and crackers
The next two meals added antioxidants to olive oil;
Meal 4: Extra-virgin olive oil, non-preservative-containing whole-grain bread, 1 gm of Vitamin C and 800 IU of Vitamin E
Meal 5: Extra-virgin olive oil, non-preservative-containing whole-grain bread, 100 ml balsamic vinegar, 1.5 cups romaine lettuce, 1 medium-sized carrot and 1 medium-sized tomato
Contrary to expected results, Meal 1 impaired blood flow through the brachial artery by 31%. The other four meals did not significantly reduce blood flow. All five meals raised triglyceride levels.
The mechanism of the reduction in blood flow through the brachial artery appeared to be an increase in oxidative stress. The antioxidant additions of Vitamins C and E in Meal 4 and of balsamic vinegar and salad in Meal 5 reduced the impairment of blood flow caused by olive oil by 71% and 65% respectively. Study investigators concluded that it is the accompanying antioxidant-rich foods in a diet that are exerting the beneficial effects on blood vessels, not the olive oil (15).
These results were strengthened further by a 2007 study looking at effects of the ingestion of large amounts of olive, soybean and palm oils, both fresh oil and oil after deep frying, on endothelial function. Results revealed that all these oils, whether they were fresh or deep-fried, caused approximately 32% acute impairment of the endothelium along with increasing blood triglyceride levels (16)
Another study assessed the healthiness role of specific dietary factors in the southern Mediterranean population of Crete, Greece. It was discovered that residents with established heart disease had significantly higher intakes of fat overall as well as high intake of monounsaturated fats principally from olive oil (17).
Yet another study looked at the effects of adding 25 ml olive oil soaked into bread or 40 g shelled walnuts to a meal already high in fat. The olive oil did not improve endothelial function, however, the walnuts did (18).
Olive oil intake is also linked to inflammation. Ingesting oleic acid, the monounsaturated fatty acid that makes up most of the fatty portion of olive oil, promotes the attachment of lipopolysaccharides (toxic substances from the membranes of bacteria) to chylomicrons in the bloodstream (19). Both lipopolysaccharides and chylomicrons cause increased inflammation (20). Chylomicrons are large fatty cholesterol remnants that are a significant component of the plaques that build up in artery walls during atherosclerosis (21). Presence of chylomicrons and other cholesterol remnants in the blood have been found to increase the risk of coronary heart disease events such as heart attacks and strokes. Studies have concluded that each 1 mmol increase in blood levels of remnant cholesterol resulted in almost tripling of these risks (21,22).
Doesn’t olive oil lower “bad” LDL-cholesterol and increase “good” HDL-cholesterol?
Let’s look at lowering LDL-cholesterol first
The high level of monounsaturated fatty acids in olive oil is often pointed out as a reason why olive oil is heart healthy. But is this true? Studies generally have found few associations between ingestion of monounsaturated fats and detrimental cardiovascular effects. Conversely, beneficial effects have been unclear and the impact of monounsaturated fats on blood lipid levels are controversial. There is strong evidence however that when monounsaturated fatty acids REPLACE saturated fatty acids in the diet various cardiovascular risk factors are improved (23).
In the US, health claims for products must accurately communicate to consumers the scientific evidence supporting the claim. The US Food and Drug Administration requires that claims for the effect of monounsaturated fatty acids from olive oil on coronary heart disease must contain the following information;
Limited but not conclusive scientific evidence suggests that eating about 2 tablespoons (23 grams) of olive oil daily may reduce the risk of coronary heart disease due to monounsaturated fat in olive oil. To achieve this possible benefit, olive oil must replace a similar amount of saturated fat and not increase the total number of calories eaten in a day. (24)
In other words, adding olive oil to a diet does not lower LDL-cholesterol levels or reduce the risk of heart disease. Heart benefits from olive oil result ONLY when the olive oil is replacing an equivalent amount of saturated fat. It is the removal of saturated fat from the diet that is reducing heart disease risk (24). Additionally, replacing saturated fat with high-quality carbohydrates such as whole grains, fruits, vegetables, nuts, seeds and legumes provides similar LDL-cholesterol lowering power (25,26).
Studies of Mediterranean diets in Greece have calculated that the biggest benefit to health from Mediterranean diets stem from their inclusion of an abundance of plant foods, including fruits, vegetables, whole grains, nuts and legumes, along with low meat intake and moderate alcohol consumption (27,28). A high ratio of monounsaturated fat to saturated fat in a diet contributes only 11% of the observed reduction in heart disease from such diets (27). By the way, monounsaturated fats in a Mediterranean diet are derived not only from olive oil, but also from other plant foods such as nuts (almonds, cashews, pecans, hazelnuts, macadamia nuts, pistachios), legumes (peanuts) and seeds (sesame, sunflower, pumpkin and flaxseeds), some species of fish (herring, halibut, mackerel), high-fat vegetables such as avocados, and other vegetable oils (29).
What about HDL-cholesterol?
Does olive oil raise HDL, the so-called “good” cholesterol? Studies suggest that this is so (30,31). But is it even relevant (32)? Though HDL-cholesterol has been reported to have beneficial cardio-protective properties (33), interventional clinical trials have failed to show that that high HDL-cholesterol levels are associated with any significant improvements on cardiovascular health (34,35).
Increasingly evidence is revealing that it is the quality of HDL particles and not their quantity in the diet that is important for lowering cardiovascular disease risk. New research has shown that HDL is vulnerable to corruption and conversion into a destructive form. A protein called apolipoprotein-A1 (apoA1) present in HDL provides the mechanism for the transfer of cholesterol out of the artery wall and into the liver from which it can be excreted. However, in diseased and inflamed arteries a large proportion of apoA1 becomes oxidized, rendering HDL dysfunctional and in fact making it promote inflammation and atherosclerosis instead of being heart protective (36). Other investigations have also shown that very high HDL levels actually increase the risk of premature death from cardiovascular disease to the same extent as do low HDL levels (37,38,39).
Happily there is good news to be found here. Though people eating a healthier diet such as a plant-based diet tend to have lower than average HDL levels, they also have lower rates of heart disease (40,41).
Wrapping it all up…
Olive oil is made up of virtually 100% fat and 14% of that fat is saturated. Currently health organizations such as the American Heart Association recommend a dietary pattern that provides no more than 5 to 6% of its calories from saturated fat with the goal of reducing cardiovascular disease (42).
Eating excess quantities of any fat, including olive oil, is associated with obesity.
Olive oil is not a good source of antioxidants.
Olive oil does not lower LDL-cholesterol.
Olive oil may cause a slight increase in HDL-cholesterol but this appears to be a moot point when it comes to cardiovascular disease risk. Both low- and high-HDL levels are associated with increased risk of heart disease.
Olive oil consumption is not associated with lower risk of cardiovascular disease. All oils, including olive oil, have a crippling effect on blood vessels.
Eating olive oil is linked with increased inflammation and higher risks of risk of coronary heart disease events such as heart attacks and strokes.
Olive oil is not a health food. If you are healthy and genuinely enjoy the taste and texture of olive oil, you can probably get away with treating yourself occasionally to small amounts. Generally though, use olive oil as a seasoning, not a major ingredient in your diet. On the other hand, if you are struggling with excess weight or suffering from cardiovascular disease it would be to your benefit to find healthier alternatives in your diet for all added oils.
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