Page last updated: April 22, 2013
Primary prevention of cardiovascular disease with a Mediterranean diet

About 30 percent of heart attacks, strokes and deaths from heart disease can be prevented in people at high risk if they switch to a Mediterranean diet rich in olive oil, nuts, beans, fish, fruits and vegetables, and even drink wine with meals, a large study has found.

Previous observational cohort studies and a secondary prevention trial have shown an inverse association between adherence to the Mediterranean diet and cardiovascular risk. Researchers in Spain conducted a randomized trial of this diet pattern for the primary prevention of cardiovascular events.

In a multicenter trial in Spain, participants who were at high cardiovascular risk, but with no cardiovascular disease at enrollment were randomly assigned, to one of three diets. One group was assigned to a Mediterranean diet and was given extra-virgin olive oil each week with instructions to use at least 4 four tablespoons a day. The second group was also assigned the Mediterranean diet but with a combination of walnuts, almonds and hazelnuts and instructions to eat about an ounce of the mix each day. The third group were assigned to a low fat diet.

The Mediterranean diet consisted of at least three servings a day of fruits and at least two servings of vegetables. Participants were to eat fish at least three times a week and legumes, which include beans, peas and lentils, at least three times a week. They consumed white meat instead of red, and, for those accustomed to drinking, at least seven glasses of wine a week with meals. They avoided commercially made cookies, cakes and pastries and limited their consumption of dairy products and processed meats.

In order to assess compliance with the Mediterranean diet, researchers measured levels of a marker in urine of olive oil consumption - hydroxytyrosol - and a blood marker of nut consumption - alpha-linolenic acid.  Investigators reported that the participants adhered  to the Mediterranean diet, but those assigned to a low-fat diet did not lower their fat intake very much. The controls therefore provided a comparison against a typical modern diet, with a regular consumption of red meat, sodas and commercial baked goods.

The study assessed the rate of major cardiovascular events (myocardial infarction, stroke, or death from cardiovascular causes).

A major cardiovascular event occurred in 288 participants. The multivariable-adjusted hazard ratios were 0.70 (95% confidence interval [CI], 0.54 to 0.92) and 0.72 (95% CI, 0.54 to 0.96) for the group assigned to a Mediterranean diet with extra-virgin olive oil (96 events) and the group assigned to a Mediterranean diet with nuts (83 events), respectively, versus the control group (109 events). No diet-related adverse effects were reported.  On the basis of the results of an interim analysis, the trial was stopped after a median follow-up of 4.8 years.

The authors  conclude that among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the incidence of major cardiovascular events.  The diet helped those following it even though they did not lose weight and most of them were already taking statins, or blood pressure or diabetes drugs to lower their heart disease risk.

“Really impressive,” said Rachel Johnson, a professor of nutrition at the University of Vermont and a spokeswoman for the American Heart Association. “And the really important thing  is that they used very meaningful endpoints. They did not look at risk factors like cholesterol or hypertension or weight. They looked at heart attacks and strokes and death. ”

Heart disease experts said the study was impressive because it showed that a diet was powerful in reducing heart disease risk, and it did so using the most rigorous methods.

The study, by Dr Ramon Estruch, a professor of medicine at the University of Barcelona, and his colleagues, was long in the planning. Dr Estruch said he thought the effect of the Mediterranean diet was due to the entire package, not just the olive oil or nuts. He did not expect, though, to see such a big effect so soon. “This is actually really surprising to us,” he said.

The researchers were careful to say in their paper that while the diet clearly reduced heart disease for those at high risk for it, more research was needed to establish its benefits for people at low risk. But Dr Estruch said he expected it would also help people at both high and low risk, and suggested that the best way to use it for protection would be to start in childhood.

Source: Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Ramón Estruch, et al. New England Journal of Medicine, February 25, 2013

www.nejm.org/doi/full/10.1056/NEJMoa1200303

 

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