Consuming a Mediterranean diet rich in virgin olive oil may protect the heart.
Montserrat Fitó, Ph.D., was the senior author of the new research and coordinator of the Cardiovascular Risk and Nutrition Research Group at the Hospital del Mar Medical Research Institute in Barcelona, Spain, as well as the Ciber of Physiopathology of Obesity and Nutrition, also in Spain. Fitó and team's findings were published in the American Heart Association's journal Circulation.
There are two types of molecules called lipoproteins that carry cholesterol in the blood: low-density lipoprotein (LDL) and high-density lipoprotein (HDL).
LDL is known as "bad" cholesterol, since having high levels of LDL can bring about plaque buildup in the arteries, which can result in heart disease and stroke. HDL is known as "good" cholesterol; HDL absorbs cholesterol and carries it to the liver where it is flushed from the body. Having high levels of HDL reduces heart disease and stroke.
Mediterranean diets compared with healthy control diet
A growing body of evidence supports the theory that the Mediterranean diet protects against the development of heart disease. Studies have also shown that the Mediterranean diet improves the lipid profile of HDLs.
"However, studies have shown that HDL doesn't work as well in people at high risk for heart attacks, strokes, and other cardiovascular diseases and that the functional ability of HDL matters as much as its quantity," explains Fitó. "At the same time, small-scale trials have shown that consuming antioxidant-rich foods like virgin olive oil, tomatoes, and berries improved HDL function in humans. We wanted to test those findings in a larger, controlled study," she adds.
The research team aimed to determine whether eating a Mediterranean diet enriched with virgin olive oil or nuts over a long period of time would improve the beneficial properties of HDL in humans.
Fitó and collaborators randomly selected a total of 296 individuals who had a high risk of heart disease and were participating in the Prevención con Dieta Mediterránea study. The participants had an average age of 66 and were assigned to one of three diets for a year.
The first diet was a traditional Mediterranean diet enriched with around 4 tablespoons of virgin olive oil per day. The second, a traditional Mediterranean diet supplemented with a fistful of nuts each day. The third diet was a healthful "control" diet that contained a reduced amount of red meat, high-fat dairy products, processed foods, and sweets.
Both Mediterranean diets emphasized the inclusion of fruit, vegetables, legumes (such as beans, chickpeas, lentils, and whole grains), and moderate amounts of fish and poultry.
Blood tests were conducted at the start and end of the study to measure LDL and HDL levels.
Virgin olive oil-enriched Mediterranean diet enhanced HDL function
The researchers found that total and LDL cholesterol levels were only reduced in the healthful control diet. While none of the three diets significantly increased HDL levels, the two Mediterranean diets improved HDL function, and the improvement was more pronounced in the group enriched with virgin olive oil.
The Mediterranean diet enriched with virgin olive oil improved HDL functions, such as reversing cholesterol transport, providing antioxidant protection, and enabling vasodilation.
Reverse cholesterol transport is the process in which HDL removes cholesterol from plaque in the arteries and takes it to the liver. Antioxidant protection is the ability of HDL to counteract the oxidation of LDL. Oxidation of LDL triggers the development of plaque in the arteries.
Lastly, vasodilator capacity - which relaxes the blood vessels, keeps them open, and keeps the blood flowing - is improved by the Mediterranean diet with virgin olive oil.
Although the control diet was rich in fruits and vegetables like the two Mediterranean diets, the diet was shown to have an adverse impact on HDL's anti-inflammatory properties. This negative impact was not observed in the Mediterranean diets. A reduction in HDL's anti-inflammatory capacity is linked with a greater risk of heart disease.
As expected, the researchers only found slight differences in results between the diets, because the variation between the two Mediterranean diets was modest, and the control diet was healthful.
"Following a Mediterranean diet rich in virgin olive oil could protect our cardiovascular health in several ways, including making our 'good cholesterol' work in a more complete way."
This research could contribute to the development of novel therapeutic targets, such as new antioxidant-rich foods, nutraceuticals, or new drug families that may improve HDL function, conclude the study authors.