Olive oil has long been touted as an essential part of the healthy Mediterranean diet, but new evidence appears to show exactly why - it helps reduce the oxidation of LDL of 'bad' cholesterol, linked to the hardening of the arteries.
Writing in the April edition of the European Journal of Clinical Nutrition, a team led by Dr M. C. Lopez-Sabater from the University of Barcelona said they had calculated that LDL or 'bad' cholesterol levels could be cut substantially after consuming just 25 millilitres of virgin olive oil daily for one week.
Dr Lopez-Sabater's team focused on just 16 people, all of whom were told to avoid foods such as coffee, tea, wine and vegetables for a period of four days. These types of food contain phenols, antioxidant products which can help attack harmful free radicals, and the researchers wanted to ascertain whether the oil would also increase phenol levels.
Once they had avoided phenol-rich foods for four days, the 16 subjects were given 50 mL of virgin olive oil and were then told to avoid all other foods containing phenols for a further 24 hours. After that, they simply ate regularly for the next week, although they continued to take a supplement of 25 mL of olive oil a day.The volunteers also avoided high-fat foods such as butter, margarine, cooking oil, nuts, baked foods and eggs.
After just one week of supplementation with olive oil, the blood samples taken from the participants were found to contain higher levels of antioxidants such as vitamin E and phenols. There were also higher levels of oleic acid, the predominant type of fat in olive oil, and monounsaturated fatty acids, both of which are indicative of reduced LDL oxidation rate, the researchers said.
The researchers stressed that while all types of olive oil are sources of monounsaturated fat, the fact that virgin olive oil is less processed than others means that it also contains higher levels of antioxidants.
Other types of phenols - notably those found in products such as red wine and onions - have been shown to help control cholesterol, but little is yet known about the potential benefits if olive oil. "Our results support the idea that daily ingestion of virgin olive oil could protect LDL from oxidation," Lopez-Sabater said in the article.
"In addition to the LDL-lowering effect of virgin olive oil, our results suggest that an intake of 25 mL/day could increase the resistance of LDL to oxidation because it becomes richer in oleic acid and antioxidants. These benefits could be achieved by including virgin olive oil daily in our diet."