Diets rich in olive oil, which contains up to 80% oleic acid, reduce blood pressure, studies have shown. Now, researchers have demonstrated that oleic acid itself is responsible for the oil's hypotensive effect.
Scientists previously surmised that minor components such as α-tocopherol and polyphenols are responsible for olive oil's blood-pressure-lowering effect. In the new work, John E. Halver, a biochemist and professor emeritus of nutrition at the University of Washington, Seattle, and colleagues find that rats consuming oils high in oleic acid have low blood pressure (Proc. Natl. Acad. Sci. USA 2008, 105, 13811).
The researchers suggest oleic acid incorporates into the cell membranes of blood vessels where it likely makes the cells more receptive to signals that reduce blood pressure. Halver suggests that the incorporation occurs because oleic acid's cis configuration allows it to pack densely into membranes. Oleic acid's trans isomer, commonly known as elaidic acid, and soybean oil, which has little oleic acid, do not lower rats' blood pressure, the team finds.
The data suggest that consuming olive oil reduces blood pressure because of oleic acid's physical properties and not through complex metabolic pathways as scientists had suspected, says Wallace H. Yokoyama, a USDA research chemist in Albany, Calif. "A simple geometric difference—cis versus trans—in an 18-carbon fatty acid leads to significant differences in membrane fluidity despite the fact that oleic acid makes up a very small percentage of the membrane," he adds.