It's good for your health to have olive oil in salad. A British study published on Monday could tell you why: unsaturated fats with nitrite-rich vegetables can protect you from hypertension.

Mediterranean diet typically includes unsaturated fats found in olive oil, nuts and avocados, along with vegetables like spinach, celery and carrots that are rich in nitrites and nitrates. Previous studies have shown that this kind of diet can reduce blood pressure.

A group of British researchers led by King's College London (KCL) reported that, when these two food groups are combined, the reaction of unsaturated fatty acids with nitrogen compounds in the vegetables results in the formation of nitro fatty acids.

In their new study, researchers used mice to investigate the process in which these nitro fatty acids lower blood pressure, looking at whether they inhibited an enzyme known as soluble Epoxide Hydrolase which regulates blood pressure.

Mice genetically engineered to be resistant to this inhibitory process were found to maintain their high blood pressure despite being fed the type of nitro fatty acids that normally form when a Mediterranean diet is consumed.

However, nitro fatty acids were found to lower the blood pressure of normal mice following the same diets.

Professor Philip Eaton at KCL, who led the study, said: "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."