Most of us will be only too aware of the importance of moderating the amount of fat in our diets. However, in our apparent rush towards low-fat eating, it can be easy to miss out on the benefits of healthy fats known as essential fatty acids (EFAs). Unlike the fats found in meat and dairy products, EFAs may actually reduce the risk of conditions such as heart disease and stroke. One fat which has been singled out for special attention in this respect is olive oil. A high consumption of olive oil is thought to explain, at least in part, why Mediterranean races such as the Southern Italians and Greeks have such low rates of heart disease. Recently, however, I became aware of a report published in the medical journal The Lancet claiming that the proposed health benefits of olive oil are overstated and unjustified. The article suggests that many vegetable oils offer just as many, if not more, health benefits in the long term. So, does olive oil really possess some unique disease-protective properties, or is its reputation merely the result of marketing hype?
Fats and oils, technically known as ‘lipids’, come in three basic forms; saturated, polyunsaturated and monounsaturated. In saturated fat, found mainly in meat, eggs and dairy products, have been linked with an increased risk of heart disease, while poly- and monounsaturated fat are believed to help maintain health and protect the body from disease. Many of olive oil’s healthy properties have been attributed to a form of monounsaturated fat known as ‘oleic acid’.
In the report in The Lancet, the authors cast doubt on the benefits of oleic acid by quoting a study which looked at the potential benefits of a Mediterranean diet. They discuss research which found individuals switching to a Mediterranean diet were at reduced risk of a second heart attack. In this study, the authors argued, it was not olive oil, but a margarine based on rapeseed oil, that was used by individuals on the ‘Mediterranean’ diet. Rapeseed oil is rich in a polyunsaturated fat know as alpha-linolenic acid (ALNA). Like oleic acid in olive oil, ALNA is an healthy fat and has traditionally been linked to a reduced risk of heart disease. However, whatever the relative merits of ALNA are, the fact remains that Mediterranean races enjoy relatively low rates of heart disease, and it is olive oil (not rapeseed oil-based margarine) that is the predominant fat in their diet.
One of olive oil’s effects is to reduce cholesterol levels in the bloodstream. In the paper in the Lancet, the authors claim that most other poly- and monounsaturated vegetable oils actually have more potent cholesterol-lowering actions than olive oil. This may be true, but it should not be assumed that a reduction in cholesterol level necessarily means a lower risk of heart disease. For instance, one study published in the British Medical Journal in 1965 found that while the addition of vegetable oil (corn oil) to the diet reduced cholesterol levels, it actually increased the risk of heart attack.
When looking at the impact of cholesterol on the body, we need to look far beyond just the level of this fat in the bloodstream. It is well known from studies in animals that it is when cholesterol reacts with oxygen (becomes ‘oxidised’) that it is toxic to the body. It turns out that olive oil contains a number of compounds, including oleuropein and squalene, which have the ability to protect cholesterol from oxidation. The presence of these so-called ‘antioxidants’ in olive oil helps to explain its ability to reduce the risk of heart disease. Moreover, these compounds might also help to reduce the risk of other conditions related to oxidation such as cancer. One study, for instance, found that women consuming more olive oil had a significantly reduced risk of breast cancer.
One final point the authors make to damn olive oil relates to its supposed impact on weight. The suggestion here is that because olive oil is a fat, its addition to the diet might increase calorie intake, thereby increasing weight as it does this. The only study I could find in the scientific literature that examined the effect of olive oil on weight did not support this theory. In this study, mildly obese women were put on a diet which was high in fat (45 p.c. of total calories), chiefly because the diet had been enriched with large quantities of olive oil. Compared to women who made no dietary changes, the diet rich in olive oil was effective for weight loss.
Clearly, the balance of evidence still supports the use of olive oil in the diet. Regular consumption of olive oil, either as the base for salad dressing or to cook in, is likely to have considerable health benefits in the long term. The best olive oil is what is known as ‘cold pressed’ ‘extra virgin’ olive oil. This unprocessed, non-heat-treated oil from the first pressing of olives is believed to have the most health-giving properties.