Pour on the olive oil, preferably over fish and vegetables: One of the longest and most scientific tests of a Mediterranean diet suggests this style of eating can cut the chance of suffering heart-related problems, especially strokes, in older people at high risk of them.

The study lasted five years and involved about 7,500 people in Spain. Those who ate Mediterranean-style with lots of olive oil or nuts had a 30 percent lower risk of major cardiovascular problems compared to those who were told to follow a low-fat diet but who in reality, didn't cut fat very much. Mediterranean meant lots of fruit, fish, chicken, beans, tomato sauce, salads, and wine and little baked goods and pastries.

Mediterranean diets have long been touted as heart-healthy, but that's based on observational studies that can't prove the point. The new research is much stronger because people were assigned diets to follow for a long time and carefully monitored. Doctors even did lab tests to verify that the Mediterranean diet folks were consuming more olive oil or nuts as recommended.

Most of these people were taking medicines for high cholesterol and blood pressure, and researchers did not alter those proven treatments, said one study leader, Dr. Ramon Estruch of Hospital Clinic in Barcelona.

But as a first step to prevent heart problems, "we think diet is better than a drug" because it has few if any side effects, Estruch said. "Diet works."

Results were published online Monday by the New England Journal of Medicine and were discussed at a nutrition conference in Loma Linda, Calif.

People in the study were not given rigid menus or calorie goals because weight loss was not the aim. That could be why they found the "diets" easy to stick with – only about 7 percent dropped out within two years. There were twice as many dropouts in the low-fat group than among those eating Mediterranean-style.

Researchers also provided the nuts and olive oil, so it didn't cost participants anything to use these relatively pricey ingredients. The type of oil may have mattered – they used extra-virgin olive oil, which is minimally processed and richer than regular or light olive oil in the chemicals and nutrients that earlier studies have suggested are beneficial.

The study involved people ages 55 to 80, just over half of them women. All were free of heart disease at the start but were at high risk for it because of health problems – half had diabetes and most were overweight and had high cholesterol and blood pressure.

They were assigned to one of three groups: Two followed a Mediterranean diet supplemented with either extra-virgin olive oil (4 tablespoons a day) or with walnuts, hazelnuts and almonds (a fistful a day). The third group was urged to eat a low-fat diet heavy on bread, potatoes, pasta, rice, fruits, vegetables and fish and light on baked goods, nuts, oils and red meat.

Independent monitors stopped the study after nearly five years when they saw fewer problems in the two groups on Mediterranean diets.

Doctors tracked a composite of heart attacks, strokes or heart-related deaths. There were 96 of these in the Mediterranean-olive oil group, 83 in the Mediterranean-nut group and 109 in the low-fat group.

Looked at individually, stroke was the only problem where type of diet made a big difference. Diet had no effect on death rates overall.

The Mediterranean diet proved better even though its followers ate about 200 calories more per day than the low-fat group did. The study leaders now are analyzing how each of the diets affected weight gain or loss and body mass index.

The Spanish government's health research agency initiated and paid for the study, and foods were supplied by olive oil and nut producers in Spain and the California Walnut Commission. Many of the authors have extensive financial ties to food, wine and other industry groups but said the sponsors had no role in designing the study or analyzing and reporting its results.

Rachel Johnson, a University of Vermont professor who heads the American Heart Association's nutrition committee, said the study is very strong because of the lab tests to verify oil and nut consumption and because researchers tracked actual heart attacks, strokes and deaths – not just changes in risk factors such as high cholesterol.

"At the end of the day, what we care about is whether or not disease develops," she said. "It's an important study."

Rena Wing, a weight-loss expert at Brown University, noted that researchers provided the oil and nuts, and said "it's not clear if people could get the same results from self-designed Mediterranean diets" – or if Americans would stick to them more than Europeans who are used to such foods.

Dr. George Bray of the Pennington Biomedical Research Center in Baton Rouge, La., said he would give the study "a positive – even glowing – comment" and called it "the best and certainly one of the largest prospective dietary trials ever done."

"The data are sufficiently strong to convince me to move my dietary pattern closer to the Mediterranean Diet that they outline," he added.

Another independent expert also praised the study as evidence diet can lower heart risks.

"The risk reduction is close to that achieved with statins," cholesterol-lowering drugs, said Dr. Robert Eckel, a diet and heart disease expert at the University of Colorado.

"But this study was not carried out or intended to compare diet to statins or blood pressure medicines," he warned. "I don't think people should think now they can quit taking their medicines."

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Online:

Journal: http://www.nejm.org

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Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP

Earlier on HuffPost:

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  • 1. Ornish Diet

    Dieters are sure to do their heart a favor on <a href="http://health.usnews.com/best-diet/ornish-diet">the Ornish diet</a>, according to experts, and if they use a rigorous version of the plan they could actually reverse heart disease. But the balanced, sound menu promotes heart health only <em>if</em> -- experts emphasized if -- the diet's rules are followed.

  • 2. TLC Diet

    <a href="http://health.usnews.com/best-diet/tlc-diet">The Therapeutic Lifestyle Changes (TLC) diet</a> helps keep cardiovascular disease at bay, according to experts who reviewed the research. Following the diet should bring down blood pressure and improve cholesterol levels, for example.

  • 3. DASH Diet

    <a href="http://health.usnews.com/best-diet/dash-diet">The Dietary Approaches to Stop Hypertension program, or DASH</a>, was devised to help control high blood pressure, and its effects on that marker of cardiovascular health have been extensively studied. So it's no surprise that experts regarded it as a good diet for the heart.

  • 4. Mediterranean Diet

    Lots of research has validated <a href="http://health.usnews.com/best-diet/mediterranean-diet">the Mediterranean diet's</a> ability to prevent cardiovascular disease because of its emphasis on produce, monounsaturated fats, and protein from fish, with only a small amount from red meat.

  • 5. Engine 2 Diet

    The <a href="http://health.usnews.com/best-diet/engine-2-diet">Engine 2 diet</a> earned 3.9 stars, and experts were impressed with its positive affect on heart health. Following this low-fat, vegan plan should help keep cholesterol and blood pressure in check and heart disease at bay.

  • 5. Vegan Diet

    <a href="http://health.usnews.com/best-diet/vegan-diet">Veganism</a> earned high marks for its potential to boost cardiovascular health. It emphasizes the right foods -- fruits, veggies and whole grains -- while steering dieters away from salty, processed choices.

  • 7. Flexitarian Diet

    <a href="http://health.usnews.com/best-diet/flexitarian-diet">The Flexitarian diet</a> earned an above-average score, which means it has the potential to decrease the risk of cardiovascular disease. Research suggests that eating patterns heavy on fruits, veggies, and whole grains help promote healthy blood pressure and cholesterol levels.

  • 8. Anti-Inflammatory Diet

    <a href="http://health.usnews.com/best-diet/anti-inflammatory-diet">The Anti-Inflammatory diet</a>, which is based on the heart-healthy principles of the Mediterranean diet, earned an above-average 3.6 stars. It emphasizes the consumption of omega-3 fatty acids, which are found in oily fish and have been linked to a lowered risk of heart disease and other chronic illnesses.

  • 8. Mayo Clinic Diet

    Experts saw <a href="http://health.usnews.com/best-diet/mayo-clinic-diet">the Mayo Clinic Diet</a> as a sound option for preventing or controlling heart problems. Its focus is on coaching dieters to develop healthy, lasting habits around which foods they choose to eat and which to avoid.

  • 8. Vegetarian Diet

    A <a href="http://health.usnews.com/best-diet/vegetarian-diet">vegetarian diet</a> has the potential to decrease the risk of cardiovascular disease, according to experts, as long as vegetarians don't load up on full-fat dairy and processed foods. It's a good bet for heart-conscious dieters, especially those who don't have the heart to eat animals anyway.

  • 11. Biggest Loser Diet

    <a href="http://health.usnews.com/best-diet/biggest-loser-diet">The Biggest Loser diet</a> scored above average in the heart category. It mirrors the medical community's consensus about what makes a heart-healthy plan. It's heavy on fruits, vegetables, lean protein and whole grains, and light on saturated fat and added sugar. And exercise is integral to the program, not an add-on.

  • 11. Volumetrics Diet

    Research indicates <a href="http://health.usnews.com/best-diet/volumetrics-diet">Volumetrics</a> can improve cardiovascular health, and the diet reflects the essence of a heart-healthy approach to eating: It's heavy on fruits, veggies and whole grains, and light on saturated fat and salt.

  • 13. Weight Watchers Diet

    <a href="http://health.usnews.com/best-diet/weight-watchers-diet">Weight Watchers</a> is a healthy diet for the heart, according to experts, but it's not as strong in this area as it is for weight loss. Some evidence suggests it helps lower cholesterol and triglyceride levels, potentially warding off heart problems. And weight loss can help prevent heart disease.

  • 14. Eco-Atkins Diet

    <a href="http://health.usnews.com/best-diet/eco-atkins-diet">Eco-Atkins</a> performed moderately well when experts evaluated it as a diet for the heart. Research supports their view. One study, for example, found that those who followed the diet had a 23 percent lower risk of dying from heart disease than those who opted for a low-carb diet heavy on meat.

  • 14. Traditional Asian Diet

    <a href="http://health.usnews.com/best-diet/traditional-asian-diet">The Asian diet</a> received a moderate 3 out of 5 stars. Little research connects it to cardiovascular benefits but on the plus side, the eating pattern is low in saturated fat and high in fiber from fruits, vegetables, whole grains and rice.

  • 16. Flat Belly Diet

    <a href="http://health.usnews.com/best-diet/flat-belly-diet">The Flat Belly diet</a> is a moderately effective choice for managing or preventing heart disease, our experts concluded. The plan emphasizes monounsaturated fatty acids, which research suggests are good for the heart. Plus, dieters could benefit if Flat Belly delivers on its promise to whittle down belly fat -- a risk factor for heart disease.

  • 16. Jenny Craig

    Experts weren't impressed by research suggesting that <a href="http://health.usnews.com/best-diet/jenny-craig-diet">Jenny Craig</a> might improve blood pressure, and deemed it only moderately effective for preventing or reducing the risk of cardiovascular disease. However, Jenny has been found to deliver weight loss, and that could lead to improved heart health.

  • 16. Macrobiotic Diet

    The <a href="http://health.usnews.com/best-diet/macrobiotic-diet">macrobiotic</a> approach received modest ratings as a heart program. Some research suggests positive effects on levels of cholesterol and triglycerides, but panelists were not persuaded.

  • 19. South Beach Diet

    Although it was designed as a heart-healthy diet to reduce levels of fat in the blood, <a href="http://health.usnews.com/best-diet/south-beach-diet">the South Beach Diet</a> didn't make the grade with our experts. But just losing weight helps ward off chronic diseases, including heart problems -- so South Beach could have a positive effect.

  • 20. Raw Food Diet

    Assessing it solely as a heart diet, the experts gave <a href="http://health.usnews.com/best-diet/raw-food-diet">the raw food diet</a> largely lackluster scores, indicating the absence of research showing cardiovascular benefits. However, it's heavy on fruits and veggies and light on saturated fat and salt, which can help keep heart disease at bay.

  • 20. Slim-Fast

    <a href="http://health.usnews.com/best-diet/slim-fast-diet">Slim-Fast</a> wasn't designed as a heart-healthy diet, and while it shouldn't increase your risk of cardiovascular problems, it's unlikely to prevent them, either. The diet received lower marks for heart health than for any other measure the experts evaluated.

  • 20. Zone Diet

    <a href="http://health.usnews.com/best-diet/zone-diet">The Zone Diet</a> received mediocre reviews from experts as a diet for heart health. Still, some research suggests it might help lower LDL cholesterol, which is a risk factor for cardiovascular disease.

  • 23. Abs Diet

    <a href="http://health.usnews.com/best-diet/abs-diet">The Abs diet</a> landed in the bottom third on this list, with 2.7 out of 5 stars. Research is lacking, so experts questioned its ability to prevent or manage heart disease. Still, the plan's emphasis on fruits, veggies and whole grains is a positive factor.

  • 23. Medifast

    Although some research suggests <a href="http://health.usnews.com/best-diet/medifast-diet">Medifast</a> may benefit heart health, experts who rated the diet weren't overly enthusiastic. Their ratings placed Medifast toward the bottom of this ranking.

  • 25. Nutrisystem

    The experts gave <a href="http://health.usnews.com/best-diet/nutrisystem-diet">Nutrisystem</a> some of its lowest scores in judging it as a diet to prevent cardiovascular disease or other heart problems.

  • 26. Glycemic-Index Diet

    In the absence of convincing research on the <a href="http://health.usnews.com/best-diet/glycemic-index-diet">glycemic-index diet's</a> purported cardiovascular benefits, experts gave it low scores as a heart-health tool.

  • 27. Atkins Diet

    The experts were concerned about the diet's fat-heavy menu and judged it accordingly. Although <a href="http://health.usnews.com/best-diet/atkins-diet">Atkins</a> scored decently in weight loss, and losing weight can reduce the risk of many heart problems, experts want to see stronger long-term research before accepting the diet's potential heart benefits.

  • 28. Paleo Diet

    The <a href="http://health.usnews.com/best-diet/paleo-diet">Paleo diet</a> is unlikely to help prevent or manage cardiovascular disease, our expert panel concluded. Most panelists, in fact, felt that evidence of any health benefit was lacking.

  • 29. Dukan Diet

    The <a href="http://health.usnews.com/best-diet/dukan-diet">Dukan diet</a> came in dead last in the heart-health category, with experts ranking it short of minimally effective. Don't expect it to have a positive effect. "Long-term research" is needed to suss out any potential benefits, according to one expert.