The so-called Mediterranean diet is thought, mostly on the basis of observational studies, to confer cardiovascular benefit. Now, Spanish researchers have put this diet to the ultimate test — a large, randomized, primary-prevention trial. About 7500 people (age range, 55–80) without known cardiovascular disease but with either diabetes or 3 non-diabetes cardiac risk factors were randomized to one of three diets:

• Mediterranean diet supplemented with extra-virgin olive oil (at least 4 tablespoons daily)
• Mediterranean diet supplemented with a daily 30-g serving of walnuts, almonds, and hazelnuts
• Low-fat control diet

During average follow-up of 5 years, the primary composite outcome (myocardial infarction, stroke, or cardiovascular-related death) occurred significantly less often in the two Mediterranean-diet groups than in the control group (8 per 1000 person-years in each Mediterranean group vs. 11 per 1000 person-years in the control group). Among the three components of the primary endpoint, only stroke was significantly lower in the intervention groups. The two Mediterranean diets did not lower all-cause mortality significantly.

Summary appeared in Journal Watch General Medicine.

Comment: Few clarifications: 

1. Depending on group allocation, either a 15-liter (1 liter per week for 15 weeks) supply of extra-virgin olive oil (®Hojiblanca and ®Fundación Patrimonio Comunal Olivarero, both from Spain) or 3-month allowances of nuts consisting of 2 Kg (15 g per day) sachets of walnuts (®California Walnut Commission, Sacramento, CA), 1 Kg (7.5 g per day) sachets of almonds (®Borges SA, Reus, Spain), and 1 Kg (7.5 g per day) sachets of hazelnuts (®La Morella Nuts, Reus, Spain) were delivered to participants in the corresponding Mediterranean diet groups during each quarterly group session.

2.  In the Mediterranean diet with nuts group researchers offered participants three types of tree nuts, walnuts, hazelnuts and almonds. As stronger evidence supports that alpha-linolenic acid-rich walnuts might offer special advantages in cardiovascular prevention, researchers supplied a higher amount of walnuts than of almonds and hazelnuts.

3. The general guidelines to follow the Mediterranean diet that dietitians provided to participants included the following positive recommendations:

1.  abundant use of olive oil for cooking and dressing dishes;
2. consumption of ≥ 2 daily servings of vegetables (at least one of them as fresh vegetables in a salad), discounting side dishes;
3. ≥ 2-3 daily servings of fresh fruits (including natural juices);
4. ≥ 3 weekly servings of legumes;
5. ≥ 3 weekly servings of fish or seafood (at least one serving of fatty fish);
6. ≥ 1 weekly serving of nuts or seeds;
7. select white meats (poultry without skin or rabbit) instead of red meats or processed meats (burgers, sausages);
8. cook regularly (at least twice a week) with tomato, garlic and onion adding or not other aromatic herbs, and dress vegetables, pasta, rice and other dishes with tomato, garlic and onion adding or not aromatic herbs. This sauce is made by slowly simmering the minced ingredients with abundant olive oil.
9. Negative recommendations are also given to eliminate or limit the consumption of cream, butter, margarine, cold meat, pate, duck, carbonated and/or sugared beverages, pastries, industrial bakery products (such as cakes, donuts, or cookies), industrial desserts (puddings, custard), French fries or potato chips, and out-of-home pre-cooked cakes and sweets.

4. The dietitians insisted that two main meals per day should be eaten (seated at a table, lasting more than 20 minutes).

5. For usual drinkers, the dietitian’s advice was to use wine as the main source of alcohol (maximum 300 ml, 1-3 glasses of wine per day). If wine intake was customary, a recommendation to drink a glass of wine per day (bigger for men, 150 ml, than for women, 100 ml) during meals was given.

6. Ad libitum consumption was allowed for the following food items: nuts (raw and unsalted), eggs, fish (recommended for daily intake), seafood, low-fat cheese, chocolate (only black chocolate, with more than 50% cocoa), and whole-grain cereals.

7. Limited consumption (≤1 serving per week) was advised for cured ham, red meat (after removing all visible fat), and cured or fatty cheeses.

CITATION:  Estruch R et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013 Feb 25.