Everyone who’s interested in diet and health has heard of ‘the Mediterranean diet’. Advocates of this dietary pattern claim that it protects against heart disease, stroke, metabolic syndrome (characterised by excess abdominal fat, blood pressure and/or glucose levels, elevated total cholesterol and decreased HDL cholesterol), many types of cancer, and even asthma, allergies, Parkinson’s disease, Alzheimer’s disease and osteoporosis (1).
There is actually a fair bit of scientific evidence for these claims. The problem is that – thanks largely to the marketing efforts of the olive oil industry, and the personal biases of many writers who have published popular books presenting their spin on the diet – most people think that the key component of the Mediterranean diet is olive oil.
When I advise my clients to cut out all extracted oils, they ask “What about olive oil? Isn’t it heart-healthy? Surely you don’t want me to cut that out!” Yes I do, and here’s why.
‘The Mediterranean diet’ as we understand it today was first characterised and promoted by the American researcher Ancel Keys. He described it as a dietary pattern high in fresh vegetables and fruits, legumes, whole grains, nuts, fish and olive oil; and low in saturated fat-rich animal foods such as dairy products, red meat and eggs.
In his Seven Countries Study, launched in 1958, he found that the inhabitants of the Greek island of Crete – the examplars of the Mediterranean diet – had the lowest rate of heart disease of the 7 populations he studied, despite consuming up to 40% of their calories from fat (mostly from olive oil and fish).
Keys concluded that replacement of saturated fat with unsaturated fat from plant sources, would bring dramatic health benefits (2) – and the Myth of Olive Oil as Heart Disease Preventer was born.
What Keys failed to acknowledge in his initial study was that the Cretans were incredibly physically active (Crete is very mountainous and at that time, most of the people walked everywhere – up to 9 miles a day!) and their overall energy (calorie/kilojoule) intake was low.
But life in modern Crete is dramatically different than in the era when Ancel Keys’ study was performed. Olive oil consumption remains high, but sedentary lifestyle, decreased consumption of fresh produce and higher intake of high-calorie, refined and animal-derived food have come to Crete.
Over 60% of adult Cretans, and 50% of Cretan children, are now overweight and rates of high blood pressure, type 2 diabetes and heart disease have skyrocketed in recent years (3).
A recent study in Crete (4) found that patients with heart disease ate significantly more olive oil than people free of heart disease, making it crystal clear that olive oil holds no magical power to stave off the health-destroying effects of inactivity and poor dietary choices.
Cretans appear to be suffering from the same delusion as Westerners who have jumped on the Mediterranean diet bandwagon – they think they can continue to eat olive oil with impunity, even if they are overweight and sedentary.
The only thing that protected their forebears from the hazards of olive oil consumption was their high activity level and plant-based, low-calorie diet.
What you need to understand is that oils impair endothelial function. What’s endothelial function? It’s the ability of the thin layer of cells that line your blood vessels, to regulate the flow of blood through those vessels, and it’s a strong predictor of your risk of having a heart attack (5). A well-functioning endothelium keeps your blood vessels reasonably dilated, which in turn lowers your blood pressure and ‘smoothes’ the flow of blood.
Endothelial dysfunction results in constricted arteries, raised blood pressure, ‘sticking’ of inflammation-producing white blood cells to the endothelial lining, and turbid blood flow which in turn increase the risk of microscopic injuries to the blood vessels (6). These injuries are ‘patched up’ with cholesterol, like you would patch up a damaged plasterboard wall with Spakfilla.
If the injuries are infrequent, the cholesterol ‘patch’ is soon reabsorbed and the artery wall is repaired with normal, healthy endothelial cells. If there are repeated injuries, the cholesterol patches aren’t reabsorbed, but instead start to form an atherosclerotic plaque, which narrows the lumen of the blood vessel (the hole through which the blood flows), eventually causing symptoms such as angina, erectile dysfunction and chronic low back pain, and increasing the risk of stroke and heart attack.
When you ingest extracted oils and fats, you impair the function of your endothelial cells for several hours (the duration of effect varies with the type of oil) and during this time period, the growth of atherosclerotic plaques accelerates precipitously.
Olive oil dramatically impairs endothelial function (7). On the other hand, nuts do not impair endothelial function in spite of their high fat content, possibly because they contain antioxidants (which decrease the oxidative stress that causes endothelial dysfunction) and arginine (which endothelial cells use to make nitric oxide, a chemical that dilates blood vessels, prevents atherosclerotic plaque from forming on the vessel walls, and keeps blood flow smooth and even by preventing platelets from sticking together)(8).
As cardiologist Robert Vogel, the pioneer of the primary test used to assess endothelial function, concluded (7):
“the beneficial components of the Mediterranean and Lyon Diet Heart Study diets appear to be antioxidant-rich foods, including vegetables, fruits, and their derivatives such as vinegar [and omega 3-rich foods].”
The bottom line: extracting an oil from the nutritional matrix that it is packaged in by nature is asking for trouble. If you want to minimise your risk of cardiovascular disease, enjoy plant foods that are naturally high in fats, such as avocado, nuts and seeds, in moderation, but leave the extracted oils out of your diet. Slim, active people with no cardiovascular risk factors can get away with some consumption of oil, but that doesn’t mean it’s good for them!