More research suggests that a Mediterranean-style diet supplemented with either virgin olive oil or mixed nuts enhances the function of HDL cholesterol.
In a subset of 296 patients at high risk of heart disease in the PREDIMED study, cholesterol efflux capacity (CEC), the first step in reverse cholesterol transport, was significantly increased at 1 year compared with baseline in those advised to eat a Mediterranean diet rich in virgin olive oil or mixed nuts rather than a reduced-fat diet.
In addition, both Mediterranean-diet groups had a trend toward improved antioxidant and endothelial functions of HDL, although the changes were statistically significant only in the Mediterranean diet–VOO group.
"For that reason, we say that especially when the Mediterranean diet is supplemented with virgin olive oil, the HDL quality and function is better," senior author Dr Montserrat Fitó (Hospital del Mar Medical Research Institute of Barcelona and CIBEROBN Institute, Spain) told heartwire from Medscape.
She noted that the differences in results between the diets were relatively small because the control diet was a healthy one, but smaller studies have also shown that antioxidant-rich foods like olive oil, tomatoes, and berries improve HDL function.
A number of medications that raise HDL-cholesterol levels have failed to improve patient outcomes, although data are not available for HDL function. The landmark PREDIMED study showed that a Mediterranean diet could cut the risk of cardiovascular events by as much as 30%. Exactly how the diet did so isn't entirely clear.
"From a public-health standpoint, it may not matter—the diet is safe and effective in preventing disease, but from a scientific standpoint it's really a fascinating question," Dr Amit V Khera (Massachusetts General Hospital, Harvard Medical School, Boston, MA), who was not involved in the study, told heartwire .
Based on research by Khera and other HDL experts, the prevailing belief is that HDL-C levels are a crude measure of the particles' function in the body. Notably, HDL-C levels in the present analysis trended lower with all three diets, even as the Mediterranean diets significantly increased CEC, the best-established HDL functionality parameter.
"I expect there will numerous cases where they [PREDIMED investigators] are able to show that the Mediterranean diet improved a circulating biomarker. But which of these changes were responsible for cutting the cardiovascular risk by 30%? It is almost impossible to tell," Khera commented.
He added, "Nevertheless, the investigators performed careful phenotyping of several HDL functional parameters. This raises the possibility that we might use a panel of such functional parameters when we are looking at new potential therapeutics to help predict which are most likely to have benefit in clinical trials."
The findings were reported online today in Circulation.