It's the Polyphenols that Make the Difference
Summarized by Robert W. Griffith, MD
Polyphenols in olive oil represent components which are unrelated to monounsaturated fatty acids, and can raise HDL -cholesterol levels and lower the risk of oxidative damage, thereby providing a degree of cardiovascular protection.
By now, most people know that olive oil is a healthy dietary addition. Indeed, many findings point to it as the chief source for the health benefits of the Mediterranean Diet. But what's the specific substance in olive oil that's carrying most of the benefits? Phenolic compounds are prime candidates. A new study, recently published in the Annals of Internal Medicine, has investigated this. Here's a summary of the report from the EUROLIVE Study.
What was done
The Effect of Olive Oil on Oxidative Damage in European Populations (EUROLIVE) was conducted in healthy men between 20 and 60 at 6 centers in Spain, Denmark, Finland, Italy and Germany (2 centers). It was a randomized cross-over study. Of more than 340 men invited to attend for screening, 200 were randomly assigned to one of 3 groups.
The participants were given 25 mL (about a tablespoonful) of 3 different olive oils in one of three sequences. The olive oils had low (2.7 mg/kg of olive oil), medium (164 mg/kg), or high (366 mg/kg) phenolic content, but were otherwise similar. They were prepared by using virgin olive oil, which is high in polyphenols, refined olive oil, which is low in polyphenols, and a mixture of the two (equal parts) for the medium polyphenol content.
The sequences given were high-medium-low, medium-low-high, and low-high-medium. Each oil was given for 3 weeks, with a 2-week washout period before each period, during which the volunteers were asked to avoid olive oil consumption.
Full physical and lab exams were given at baseline and further blood exams before and after each intervention. The latter included glucose and lipid levels as well as measures of oxidative damage to lipid levels and the antioxidant status of the participant.
What was found
The average age of participants was 33; their BMI scores averaged 24. Their baseline exam values (physical, blood, and urine) were all within normal limits.
Eighteen of the 200 participants did not complete the study, but adverse effects of olive oil intake were not responsible in any case. Urine phenol compounds increased, according to the phenol content of the olive oil consumed.
All three olive oils increased the �good' cholesterol � high-density lipoprotein (HDL) cholesterol � in the blood, decreased the total cholesterol:HDL cholesterol ratio, and decreased triglyceride levels; these changes occurred over the 3-week administration period.
Biochemical markers for oxidative stress decreased as the phenolic content increased, indicating a degree of protection from oxidation-induced changes in low-density lipoprotein (LDL) cholesterol. There was no evidence of any effects on other risk factors for cardiovascular disease (blood pressure, LDL -cholesterol levels, BMI , etc); the treatment periods were obviously too short to allow any such changes to develop.
What the findings mean
This study shows that olive oil is more than just a monounsaturated fatty acid. The polyphenol it contains has benefits on the HDL cholesterol levels and oxidative damage in addition to those conferred by its monounsaturated fatty acid nature.
The results obtained, while showing a specific effect of the oxyphenols in olive oils, do not demonstrate that they reduce cardiovascular risk factors to a marked degree. However, with the short administration periods used, it would be quite surprising if this had been achieved. Identification of the olive oil component that increases HDL -cholesterol levels is, indeed, an important finding.
Other investigators have shown similar results after the consumption of other polyphenol-rich foods, such as cocoa, pine bark extract, and green tea. This study shows the likely health advantages of virgin olive oil over refined olive oil. Virgin oil (with the higher phenolic content) comes from the first pressing of olives, while refined oil comes from later pressings. So, if you can afford it, pay a little more and buy extra virgin olive oil � it's cold-pressed and even better than virgin olive oil. Long-term use of it will help keep your HDL -cholesterol level up, and maybe reduce other cardiovascular risk factors.
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