PREDIMED: Mediterranean Diet Cuts Heart Attacks and Strokes

A large Spanish trial published on Monday in the New England Journal of Medicine found that people at high risk of heart disease who ate a Mediterranean diet with extra virgin olive oil or nuts had about 30 percent fewer heart attacks, strokes and cardiovascular deaths than people told to eat a low-fat diet. This is the PREDIMED study. Here is what it tested, what it found, and what it does and does not mean for the oil in your kitchen.

What the PREDIMED trial did

PREDIMED (Prevención con Dieta Mediterránea) was led by Dr. Ramón Estruch of the Hospital Clínic and the University of Barcelona, with research groups across Spain. It enrolled 7,447 people with major cardiovascular risk factors, such as diabetes, smoking or excess weight. None had heart disease when they joined.

They were split at random into three groups. One followed a Mediterranean diet and received extra virgin olive oil, about a liter a week. A second followed the same diet and received mixed nuts, 30 grams a day of walnuts, almonds and hazelnuts. The third, the control group, was advised to eat a low-fat diet. Dietitians saw participants every three months and ran group sessions with menus, recipes and shopping lists. To check that people really ate what they were given, the researchers measured hydroxytyrosol, a compound from olive oil, in the urine of the olive oil group.

What it found

After almost five years, the researchers counted heart attacks, strokes and deaths from cardiovascular causes. Both Mediterranean groups had about 30 percent fewer of these events than the low-fat group. The difference was clear enough that the trial was stopped early so the findings could be reported.

Outside experts were impressed by the design rather than the headline. Rachel Johnson, a nutrition professor at the University of Vermont speaking for the American Heart Association, told NPR that a randomized, controlled trial is the gold standard of research design and called it a very strong study. Antonia Trichopoulou of the University of Athens, a long-time Mediterranean diet researcher, told Olive Oil Times the findings were a strong confirmation rather than a surprise.

What it means, and what it does not

• It tested a whole way of eating plus extra virgin olive oil or nuts, not olive oil as a pill. The people also ate the vegetables, fish and pulses the diet is built on.
• Everyone in the trial was already at high risk. The result does not automatically transfer to young, healthy people, though it points the same way as years of observational research.
• The comparison was with a low-fat diet. The study adds weight to the view that swapping in healthy fats beats simply cutting fat.
• The oil in the trial was extra virgin. That is not the same product as refined “light” olive oil.

This is general information, not medical advice. Anyone with heart disease, diabetes or high cholesterol should talk to a doctor before making big changes to diet or medication.

Sources

• ScienceDaily: Mediterranean diet helps cut risk of heart attack, stroke: Results of PREDIMED study presented (February 25, 2013)
• NPR: Study: Mediterranean Diet Can Greatly Reduce Risk Of Heart Attack, Stroke (February 25, 2013)
• Olive Oil Times: Mediterranean Diet Can Reduce Risk of Stroke and Heart Attack by 30 Percent (February 27, 2013, archived)