Evidence suggests that extra virgin olive oil has beneficial health effects when consumed regularly. Studies have shown beneficial effects for olive oil consumption that include a reduction in triglycerides and increases in high density lipoprotein (HDL) cholesterol when carbohydrates are replaced in the diet, reductions in low density lipoprotein (LDL) cholesterol levels when saturated fat is replaced in the diet, and an increased resistance to oxidative stress and the oxidation of LDL. The metabolic changes that occur through consumption of extra virgin olive oil suggest that the constituents of the oil are beneficial at preventing western disease such as type 2 diabetes, cardiovascular disease and obesity. Olive oil is a complex chemical mixture. The fat content of the oil is mostly monounsaturated fatty acids, however suspended within the oil are the remnants of olives, and these particles contain large amounts of antioxidants, particularly polyphenol antioxidants, which may provide the beneficial effects of the oil.
The beneficial effects of extra virgin olive oil consumption are similar to those observed following a lowering of the glycaemic load of the diet. This suggest that olive oils may exert its beneficial physiological effects through an increased efficiency of the blood glucose system, perhaps by improving insulin sensitivity. In fact, consumption of olive oil in its extra virgin form is associated with improved glucose metabolism in human subjects. Diabetic patients consuming 33 % of their energy from a monounsaturated fatty acid diet have been observed to have a reduced requirement for insulin, when compared to a high carbohydrate diet group. Consumption of monounsaturated fatty acids have also been shown to improve postprandial glycaemia and improve lipid profiles in diabetic patients. That nuts are also rich in monounsaturated fatty acid and have similar metabolic effects to extra virgin olive oil suggests that monounsaturated fat may have particular beneficial insulin related effects in humans.
There is a lack of conclusive data as to the effect of monounsaturated fatty acids on insulin resistance in healthy individuals. However, in contrast there is a large body of evidence that antioxidants are beneficial. As extra virgin olive oil is rich in phytonutrients from olives, including vitamin E and other polyphenolic substances, regular consumption of the oil may contribute to improvements in insulin sensitivity in healthy humans. Of course consumption of whole olives would logically have a greater effect than consumption of the oil if the antioxidants were responsible for the beneficial metabolic changes. Olive oil that has been processed and refined does not retain its antioxidants and the oils within it are oxidised and therefore capable of forming free radicals in the tissues of those that consume them, leading to lipid peroxidation. Processed olive oil therefore does not share the health benefits of extra virgin olive oil, but instead likely increases the risk of developing insulin resistance.
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