By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.

It has been known for a long time that people who live in Mediterranean countries, and who eat a diet which gets its fat mainly from olive oil and is high in fruits and vegetables, have lower rates of heart disease than people who live in Northern Europe, whose diet contains more animal fat. The Lyon Diet Heart Study was designed to test whether putting people who were at high risk of heart disease on a Mediterranean type of diet would stop them from getting heart attacks. This is the second report of its results, the first having been published in 1994. The study was conducted in France.

Six hundred and five patients who had already recovered from a first heart attack were randomly selected either to continue their present diet, or to start eating a Mediterranean diet. The instructions for this group were to eat more bread, more vegetables, more fish, and less meat (replacing red meat with chicken), to eat some fruit every day, and to use canola oil and olive oil as the sources of fat. Butter and cream were replaced by a special margarine made with canola oil.

After just over two years, there was a marked reduction (of 76%) in the number of new manifestations of heart disease in the group eating the Mediterranean diet. These manifestations included heart attacks, angina, and needing a coronary bypass operation or angioplasty. The greatest reduction occurred in the numbers of non-fatal heart attacks and unstable (new onset) angina.

Blood samples were taken from the patients during the trial, and it was found that the blood of the patients eating the Mediterranean diet differed in two important ways from the blood of the control patients. First, the blood levels of antioxidants (vitamins E and C) were higher, and second, the fatty acid profile was different, with more omega-3 (particularly oleic and alpha-linolenic acids) and less omega-6 fatty acids. All of these changes could contribute to the protective effect. Interestingly, there were no changes in blood pressure or cholesterol as a result of going on the diet.

Heart attacks and unstable angina are often caused by a sudden rupture of a plaque that may initially only partially block the artery. The endothelia cells, which form the inner lining of the artery, get stretched where the plaque bulges into the artery and may tear. When this happens, a blood clot forms over the tear, and the blockage of the artery becomes complete. The Lyon and other dietary studies have observed that the rate of heart attacks may start to go down after only a few weeks on the diet; one explanation may be that omega-3 fatty acids get rapidly incorporated into the plaque and help to stabilize it.

Doctor's comments

For most people with high blood pressure, the biggest risk to health is having a heart attack. Adopting a Mediterranean type diet appears to be one of the best dietary ways of reducing this risk and may be better (and tastier!) than simply trying to reduce your intake of salt and fat. There is also recent evidence, presented at the American Heart Association's annual meeting in November 1996, that the same diet may lower blood pressure, although this was not observed in the Lyon study. It is also worth noting that the benefits from the diet were independent of any effect on blood cholesterol (both LDL and HDL). Measurement of omega-3 fatty acids in the blood is not done in routine clinical testing

Where it was published

de Lorgeril M and colleagues. Effect of a Mediterranean type of diet on the rate of cardiovascular complications in patients with coronary artery disease. Insights into the cardioprotective effects of certain nutrients. Journal of the American College of Cardiology. 1996;28:1103-8