02/27/2013 03:02 pm ET Updated Apr 29, 2013

Can Olive Oil and Nuts Prevent Heart Attacks?

A new study, just published online in the prestigious New England Journal of Medicine, was able to prove that diet -- a tasty and rather easy to keep one, at that -- was able to reduce stroke and heart disease by 30 percent.

The study, led by Dr. Ramón Estruch from Barcelona, Spain, involved 7,447 people ages 55 to 80, all at higher risk for heart disease due to diabetes or at least three risk factors for heart disease, such as obesity, smoking, high blood pressure, elevated levels of bad cholesterol, or a family history of early heart disease.

Participants were randomly assigned to one of three groups:
  • Mediterranean diet supplemented with approximately four cups a week of extra-virgin olive oil (EVOO)
  • Mediterranean diet supplemented with an additional ounce daily of walnuts, hazelnuts, and almonds
  • Control group that was counseled to eat a low-fat diet that did not include olive oil or nuts. This group received small nonfood gifts.

Both Mediterranean diet groups were encouraged to consume olive oil, nuts, fresh fruits and veggies (at least five a day), legumes, white meat and wine in moderation with meals, and discouraged from soft drinks, commercial bakery goods such as pastries and sweets, and red meat. Sofrito (a sauce made with tomatoes, onions, garlic and herbs, slowly simmered with olive oil) was also recommended -- at least two servings a week.

The control group was advised to eat low-fat dairy, fruits and veggies (at least five a day), lean fish and seafood, and discouraged from vegetable oils (including olive oil), commercial bakery goods, nuts, fried foods, red and processed fatty meat and fatty fish.

To be fair, the study doesn't really compare the Mediterranean diet to a low-fat one, because the control group didn't really adhere to a low-fat diet -- they must have found it hard. So the comparison is really between a Mediterranean diet and a "whatever goes" diet.

Although people in all three groups had similar diets before the study started, compliance with the Mediterranean diet was good, and was verified not just by participants' report, but also by measuring urinary hydroxytyrosol, a marker of olive oil intake, and blood alpha-linolenic acid, a marker of walnut consumption.

The participants were followed for the occurrence of heart attacks, strokes and death from heart disease. After an average followup of almost five years, 288 such events happened. Both Mediterranean diet groups experienced 30 percent less such events compared with the control group.

Quite encouraging! Especially since neither group was given a low-calorie diet or advised to lose weight -- which could of course reduce heart disease and stroke risk, but isn't easy to do. As a matter of fact, the Mediterranean diet with EVOO group was encouraged to eat four tablespoons of the oil each day, which is 450 calories in EVOO alone! The Mediterranean diet with nuts group was supplied with about 200 calories a day in walnuts, almonds, and hazelnuts.

What's special about this study?

The Mediterranean diet has shown its protective benefits against several diseases in many studies. A meta-analysis in the American Journal of Clinical Nutrition combined the findings of many prospective studies, pooling more than 2 million people, and showed that greater adherence to a Mediterranean diet -- in line with pretty minor lifestyle changes, like eating a good amount of fruits and some nuts -- was associated with 8 percent reduction in death, 10 percent reduction in cardiovascular illness and cardiac death, 6 percent reduction in cancer and 13 percent reduction in neurodegenerative diseases, such as Alzheimer's, and to offer some protection from stroke and mild cognitive losses.

This study adds to previous evidence, and stands out due to its scientific rigor -- it is a large, randomized controlled clinical trial, in which people were allocated by chance alone to eat in a certain way, were followed for a long time, and were compared to a control group. Its results were also so conclusive that the trial was stopped early in order to report the results and allow the control group to enjoy the benefits of the Mediterranean treatment.

What's the health-promoting ingredient in the Mediterranean diet?

So what should it be? Should we dip bread in olive oil twice a day or snack on almonds?

Let's remember that this study tested the effects of a Mediterranean diet on heart disease and stroke. As much as we'd like to learn a magic trick from its findings, we cannot conclude that avoiding commercially baked goods, avoiding soda, eating sofrito, replacing red meat with fish, or nibbling walnuts saves lives. The people in the study changed many eating habits during the study period.

The Mediterranean diet is an eating pattern, a total plan, and should adopted as one. We don't know which part of the package confers the most benefit, all we know is that the pattern works as a whole; all parts of it are probably beneficial, and it very well might be that they work in combination with each other. The Mediterranean lifestyle -- allowing for leisurely food enjoyment and social interaction -- might be just as important.

I think the Mediterranean diet would be worth adopting for the sheer pleasure of it, and the health benefits are just another great reason to go Mediterranean.

But I'd stop short of the at-least-four-tablespoons-EVOO-daily the participants in this study were advised to eat. Way too many calories -- leaves too little to play with if you're also aiming for an energy-balanced diet.

Dr. Ayala

For more by Ayala Laufer-Cahana, M.D., click here.

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