The first pressing of olives gives virgin olive oil. Refined oil comes from subsequent pressings. The former has more amounts of polyphenols than the latter.
The study was conducted on 200 healthy men of the age 20-60 years, to understand the effect of virgin olive oil on their heart.
A comparison of virgin olive oil (high level of polyphenols), refined olive oil (low level of polyphenols), and a mixture of equal amounts of the 2 olive oils (medium level of polyphenols) was carried out by the researchers.
Under the study, everyday, each participant had to consume a tablespoon of one of the oils for 3 weeks.Over the course of the study, each of the 3 oils had to be consumed by the participant for a period of 3 weeks. Before and after each 3-week period, blood samples were taken to check levels of cholesterol and other chemicals. The results, after consumption of each type of olive oil were compared.
It was found that virgin olive oil increases the level of high-density lipoprotein cholesterol ("good cholesterol") the most. An increase in the body levels of antioxidants that prevent oxidation, which may cause damage to the low-density lipoprotein cholesterol ("bad cholesterol") and increase risk of clots in blood vessels leading to heart disease, was also observed.
Virgin olive oil seems to have stronger health benefits than refined olive oil.