Does Following the Mediterranean Eating Plan Decrease the Risk of Heart Attack and Stroke?

Did you know that because of the First Amendment, anyone can write a diet book and say whatever they want, regardless of whether or not they are qualified? As a result, fad diets are a dime-a-dozen, and rates of overweight and obesity in the U.S. remain at an all-time high. At the same time, cardiovascular disease (CVD) remains the number one cause of death among men and women worldwide.    

It is well established that death rates from CVD are lower in countries that surround the Mediterranean Sea as compared to CVD death rates in the U.S. Part of this reduced risk has been attributed to the Mediterranean Eating Plan.

This dietary approach is characterized by a relatively high intake of plant-based foods such as olive oil, fruit, nuts and seeds, and vegetables, as well as a moderate intake of fish, whole grains, red wine, and sofrito (a sauce made with tomato, onion, and olive oil). Red and processed meats, as well as added sugars are limited.

Observational studies have consistently shown that adherence to a Mediterranean type of diet is strongly associated with a decreased risk of cardiovascular disease, and plausible biological mechanisms have been identified to explain this relationship.

Researchers in Spain conducted a multicenter trial to evaluate the effect two Mediterranean Diets as compared to a control diet on primary prevention of cardiovascular disease (i.e., preventing a first heart attack or stroke) in a high risk population. A total of 7447 adults between the ages of 55 to 80 years were enrolled. Although none had cardiovascular disease at baseline, all were considered to be at high risk because they had either type 2 diabetes or at least three of the following major risk factors: smoking, hypertension, abnormal blood cholesterol, overweight, or a family history of early coronary heart disease. Subjects were then randomly assigned to one of three dietary intervention groups. Group 1 consumed a Mediterranean diet supplemented with extra-virgin olive oil (nearly 1 liter per week); while Group 2 also consumed a Mediterranean diet supplemented with 1 ounce of mixed nuts per day. Group 3 (the control group) consumed a diet where they were advised to limit all dietary fats. Dietitians conducted individual and group dietary training sessions at baseline and then quarterly thereafter. Adherence to each of the 3 diets was tracked via a 14-item questionnaire on a quarterly basis. More detailed dietary questionnaires were used on a yearly basis. No restriction on total daily caloric intake was advised, nor was physical activity promoted. So just to be clear, this was not a weight loss study.

Participants were followed for an average of 5 years after their baseline exam. Heart attack, stroke, and death from cardiovascular disease were the major areas of interest during the follow-up period. There were a total of 106 heart attacks, 139 strokes, and 87 deaths from cardiovascular disease during follow-up. Relative risk of these events in the 3 diet groups is shown below in Figure 1.

Compared to the control group, the Mediterranean diet + olive oil group had a 30% reduction in risk, while the Mediterranean diet + nuts group had a nearly identical 28% reduction in risk.  

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The authors concluded that a calorie-unrestricted Mediterranean diet, supplemented with either extra-virgin olive oil or mixed nuts resulted in a substantial reduction in the risk of major cardiovascular events in the absence of weight loss and without any changes in physical activity. What made this study unique is that it was performed in a high-risk population. Recall that the Mediterranean diet is relatively high in plant-based foods, most of which are complex carbohydrates. These findings support the evidence-based 2020-2025 Dietary Guidelines for Americans, which encourage individuals to increase their intake of fruits, vegetables, whole grains, nuts, seeds, legumes, and fatty fish. On the contrary, there are a grand total of zero published long-term studies showing that very low carbohydrate diets have these same cardiovascular benefits.

Reference

Estruch, R., et al. (2013). Primary prevention of cardiovascular disease with a Mediterranean Diet. New Engl J. Med., 369(14), 1279-1290.