Among the legion of today's most popular diet regimens, the Mediterranean diet has become a poster child for healthy eating, garnering praise from nutrition experts and home gourmets alike.
But while few would dispute the health benefits of such a diet, what is it about the Mediterranean menu that makes it so healthy?
A study released Tuesday in the online edition of the British Medical Journal took aim at this very question. Researchers from the Harvard School of Public Health in Boston and the University of Athens Medical School in Greece looked at more than 23,000 Greek men and women participating in the European Prospective Investigation into Cancer and Nutrition (EPIC). Over the course of about eight and a half years, the researchers led by Harvard's Dimitrios Trichopoulos and the University of Athens' Antonia Trichopoulou compared the health of the participants against their adherence to a Mediterranean diet.
What they found was that certain foods in the diet, more than others, may offer the bulk of the nutritional benefits of the regimen.
As the authors note, that the analysis "indicates that the dominant components of the Mediterranean diet score as a predictor of lower mortality are moderate consumption of [alcohol], low consumption of meat and meat products, and high consumption of vegetables, fruits and nuts, olive oil, and legumes."
In contrast, they noted, high consumption of fish and cereals and an avoidance of dairy products in the Mediterranean diet seemed to have little to do with the benefits of the overall diet.
The authors were quick to point out that their findings could not be assumed to be universally applicable. And some diet and nutrition experts noted that examining the Mediterranean diet component by component may not be the best approach.
"In some ways, looking for the 'active ingredients' in the health benefits of the Mediterranean diet may be a distraction, since it is the overall dietary pattern that matters most to health," said Dr. David Katz, director of the Prevention Research Center at Yale University School of Medicine in New Haven, Conn. "Once you have a mostly plant based diet and eat few processed foods, almost any variation on the theme will be fine."
And some said the research ignored a main strength of the diet -- namely, what it omits.
"One of the strengths of the Mediterranean diet is what it does not contain: high amounts of sugar and preservatives," said New York-based weight and nutrition expert Dr. Jana Klauer. "The standard American diet stimulates the craving for sweet taste through overly sweetened foods."
Still, will the findings have implications for your own diet? The following pages take a closer look at what nutrition experts have to say about the various components of the Mediterranean diet.
Widely used in Mediterranean-style cooking, olive oil has become almost synonymous with the Mediterranean diet itself. The healthy reputation may be well-deserved, as the authors of the new study note that this component of the regimen appears to confer at least some of it health benefits.
Katz noted that olive oil is rich in monounsaturated fat -- a fat that is believed to which lower total cholesterol and, more specifically, levels of low-density lipoprotein (LDL) or "bad" cholesterol in the blood.
But while olive oil may indeed be healthier than other fats -- most notably the saturated fats found in meat and synthetic trans fats found in certain baked goods -- pouring too much of it into your diet can be too much of a good thing.
Olive oil is "a heart-healthy fat, to be sure," said Keith-Thomas Ayoob, director of the nutrition clinic at the Albert Einstein College of Medicine in Bronx, N.Y. "And it has excellent street cred, but there are some limits."
First of all, Ayoob said, olive oil has just as many calories per gram as other less healthy fats. So while it may not clog your arteries, it could have an unfortunate impact on your waistline.
"The more fat you have, the less food you can eat without gaining weight, so if you need volume in your diet, use olive oil but use it modestly," Ayoob said. "Just a thought, so people don't go out and start pouring olive oil over everything and thinking it'll save them."
The notion that additional helpings of fruit and vegetables lead to a healthier diet should come as little surprise to anyone who has even had a doting mother. So nutrition experts largely agreed with the researchers when they suggested that the veggie-heavy offerings of the Mediterranean diet are responsible for much of its positive health effects.
"Once again there is clear data that the healthiest foods grow in the ground," said Dr. Mitchell Roslin, director of Obesity Surgery at Lenox Hill Hospital in New York.
Ayoob agreed. "Mountains of evidence shows that the more [fruits and vegetables], the better, period," he said. "They're loaded with fiber, antioxidants, and they're where you'll find a bucket of vitamins and minerals. The challenge is to eat them every day and preferably at least one at every meal."
Fruits and vegetables also tend to pack relatively few calories into quite a bit of bulk, along with water and fiber. The upshot is that they tend to be more filling than some other calorie-dense foods -- and thus more amenable to a lower-calorie diet.
"The more you eat of these, the less you eat of other things," Katz said.
But, he added, the considerable contribution of fruits and vegetables to the Mediterranean diet equation may be the very reason why it may overshadow some of the other healthful elements of the regimen.
"Once a diet is heavily based on vegetables and fruits, it becomes tough to show much additive benefit from anything else," Katz said.
Fish and seafood are widely regarded among nutritionists to be among the healthiest of animal proteins. So it may come as a surprise to some that, according to the new analysis, these options do not appear to have much of an overall impact on the healthiness of the diet.
As the researchers note in the study, "high consumption of fish and seafood ... as components of the traditional Mediterranean diet contribute little to the ability of the Mediterranean diet score to predict mortality, at least in this Mediterranean population."
But the notion that these components of the Mediterranean diet may not be as instrumental to its success was one that stirred debate among nutrition experts. Roslin said that he feels the analysis overlooks the fact that wild fish are extremely healthy.
Dr. Carl Lavie, medical director of Cardiac Rehabilitation and Prevention at the Ochsner Heart and Vascular Institute in New Orleans, La., agreed. "In other populations, fish has been very protective, which may be applicable in our population with a high amount of obesity and [cardiovascular] risk factors," he said.
Ayoob noted, however, that the way that fish and seafood is prepared could be an important factor.
"Fatty fish tend to lower bad cholesterol and there are lots of other benefits," he said. "My advice? Keep eating fish, just don't deep-fry it and you'll have the benefit, even if this particular study didn't find much."
One aspect of the Mediterranean diet that authors agreed was a strong contributor to its success was the presence of nuts. Aside from contributing a healthy helping of unsaturated fatty acids, nuts like almonds and walnuts offer a wealth of nutrients including calcium potassium and fiber.
The research released yesterday is not the first to suggest the importance of nuts to the Mediterranean diet. A study published last December in the Journal of the American Medical Association showed that adding an extra portion of nuts to the traditional Mediterranean regimen offered a promising way to help control the risk of metabolic disease in older adults who had a high heart disease risk.
"It's high time nuts got their share of the limelight," Ayoob said. "Almonds and walnuts are favorites in the Greek diet, and they're both tied to better heart health."
Katz added that just as important as what nuts contain is what they do not. He said they tend to be free of harmful fats, as well as sugar and salt if properly prepared.
Along with nuts and vegetables, the researchers in the new study found that beans were likely to be significant contributors to the success of the Mediterranean regimen.
"No surprise here," Ayoob said. "Beans are a near miracle food. They have some protein, lots of fiber source, iron and a ton of other nutrients and adding beans to any diet makes for a better diet.
"I'd like to see a 1/2 cup of beans on everyone's plate every day," he added.
Beans are also a standout on the Mediterranean diet menu due to their versatility. Various types of beans can be added to soups, salads and pasta sauces. And because of their high protein content, they can also be used as a meat substitute -- without adding fat and cholesterol to dishes.
And while their price may have little effect on the health of those consuming them, beans are also much cheaper per pound than meat -- an important feature for more economically-strapped dieters.
The debate over what place, if any, alcoholic beverages should hold in a healthy diet has raged among health experts for decades. As for the study at hand, researchers suggested that a moderate level of alcohol consumption, traditionally from red wine, may have a protective effect against heart disease -- thus earning it a place in the winner's column among other Mediterranean diet staples.
"Regarding the components of the diet,the strongest association was regarding protection from moderate alcohol," Lavie said.
Indeed, numerous past studies have suggested that resveratrol -- a compound found in grapes, red wine, pomegranates and some other foods -- has a positive effect on heart health.
But along with the benefits, Lavie warned, comes certain risks. He noted that despite its health benefits in moderate amounts, too much alcohol can have the exact opposite effect on heart health.
So unless you can control your intake, Lavie advised, it may be best to skip the bottle.
"Navigating this path can produce a slippery slope, and alcohol and health can be a double-edged sword," he said.
As with fish and seafood, the recent analysis placed cereals near the bottom of the list as a contributor to the overall healthful nature of the Mediterranean diet. But nutrition experts said it might be too early to count out the food category, which is a renowned source of fiber and various nutrients.
"'Cereals' is a broad category," Ayoob said. "Most of the research indicates that cereal eaters have better diets.
"It's a super vehicle for getting low-fat milk and fresh fruit into people, he added. "So I'm a little skeptical of the study results here."
One reason for the relatively low placement on the list could be the fact that the food group is a broad one which could include everything from whole-grain offerings to sugar-laced breakfast treats.
"[Cereals] have the ability to exert differential affects on health because they can range from healthful choices (whole grain cereals) to less nutritious choices (processed cereals) and low-fat or no-fat dairy to whole fat products, so that may have impacted the results," noted Dr. George Blackburn, professor of nutrition medicine at Harvard Medical School.
Katz said another reason that cereals may not have had a great impact could be because the other plant-based components of the Mediterranean diet are so healthy.
"Once a diet is already based mostly on plants, the additive benefit of [cereals] may be small," he said. "They would represent a stronger benefit when used as substitutions in the typical American diet."
One of the more controversial aspects of the traditional Mediterranean diet is the fact that dairy products are generally scarce. In this most recent study, researchers found that this aspect of the Mediterranean diet did not seem to affect health greatly in one direction or the other.
But this finding is unlikely to silence the debate over the place that dairy products should hold in a healthy diet.
"If dairy intake is low-fat or fat-free, cutting out dairy may not be advantageous at all," Katz said. "If dairy intake is low in general, cutting out dairy would make a small difference. This one is hard to interpret."
Ayoob, however, noted that he believes if there was any room for improvement in the Mediterranean diet, it would involve the addition of more low-fat dairy products.
"People have already cut out too much dairy and we're seeing the consequences -- an epidemic of osteoporosis, hip fractures and more," he said. "More low-fat and fat-free dairy is what the bulk of the research tells us we need, [while keeping] the full-fat dairy to modest amounts."