Olive oil, greens explain Mediterranean diet's beneficial effect on blood pressure

The results of a new study led by King's College London in the UK may explain why a Mediterranean diet is so often linked to good health. The combination of unsaturated fats and vegetables rich in nitrites and nitrates in the diet produces a group of fatty acids whose blocking of an enzyme helps to lower blood pressure.

The authors report their findings in the journal Proceedings of the National Academy of Sciences.

The typical Mediterranean diet comprises foods rich in unsaturated fats, such as olive oil, fish, nuts and avocados, plus foods rich in nitrites and nitrates, such as leafy greens like lettuce and spinach, and other vegetables like celery and carrots.

The researchers found that consuming foods from these two groups together results in the unsaturated fatty acids reacting with the nitrogen compounds in the vegetables to make a group of compounds known as nitro fatty acids.

They ran a series of experiments on normal and genetically engineered mice to show that the nitro fatty acids help lower blood pressure by inhibiting an enzyme known as soluble epoxide hydrolase.

The authors note that previous studies have already suggested blocking soluble epoxide hydrolase lowers blood pressure.

Consuming foods like olive oil and leafy greens together results in the unsaturated fatty acids reacting with the nitrogen compounds in the vegetables to make a group of compounds known as nitro fatty acids.

The compounds that can do this "adduct" or attach themselves to a point on the enzyme molecule that is close to its "catalytic center."

This inhibits a series of reactions that in turn results in dilation of blood vessels to lower blood pressure.

For their study, the researchers engineered mice with a version of the enzyme that could not bind with nitro fatty acids and compared them with normal mice.

After administering a hormone to induce high blood pressure in the two groups of mice, the researchers then gave them nitro fatty acid supplied directly or generated via the Mediterranean diet.

Blood pressure went down in the normal mice but not in the genetically modified mice.

Nitro fatty acids help lower blood pressure by blocking enzyme

The high blood pressure hormone also caused both groups of mice to develop enlarged hearts. But, after giving the mice nitro fatty acid, the researchers saw a reduction in heart size in the normal mice but not the genetically engineered mice.

They suggest these various results show nitro fatty acids - as produced when people eat the food combinations present in the typical Mediterranean diet - block the action of the enzyme soluble epoxide hydrolase. And, this in turn leads to a series of signalling reactions that lower blood pressure.

Philip Eaton, professor of Cardiovascular Biochemistry at King's, says:

"The findings of our study help to explain why previous research has shown that a Mediterranean diet supplemented with extra-virgin olive oil or nuts can reduce the incidence of cardiovascular problems like stroke, heart failure and heart attacks."

A number of organizations, including the British Heart Foundation and the Medical Research Council UK, helped fund the study.

In February 2014, researchers reported how an analysis of studies dating from 1957 to the present day looking at links between food and heart disease found that a Mediterranean diet was better than a low-fat diet for reducing cardiovascular risk.