Here's what the research says — and doesn't say — about the Mediterranean diet.
The Mediterranean diet gets most of its fat from olive oil, and most of the fat in olive oil is monounsaturated. A high ratio of monounsaturated to saturated fat is considered an intrinsic element of the traditional Mediterranean diet -- and evidence shows that it's good for people's health.
Americans tend to like their fats saturated, their grains processed, their protein grown on legs and their sugar added anywhere their sweet tooth decides it would like some. As for fiber, they're all for it — in, say, their French fries or the pickles on their burger.
In a related development, nutrition experts tend to be bummed out by the typical American diet. In fact, many wish we'd trade it in for a diet that's pretty much the opposite, namely, the Mediterranean diet, which favors monounsaturated fat, whole (unprocessed) grains, protein with roots in the ground, sugar in its natural habitat only and fiber, well, fiber just about everywhere.
One of its champions, Dr. Dimitrios Trichopoulos of Harvard University, calls the Mediterranean way of eating "possibly the best ever."
Trichopoulos can point to hundreds of scientific studies — as well as a long-running natural experiment among Mediterranean people themselves — linking the diet to a decrease in mortality rates (meaning deaths per thousand per year) and, more specifically, to reduced rates of heart disease, Alzheimer's disease, cancer, diabetes and other serious health problems.
Probably no diet in the world has been studied more thoroughly or associated with more positive outcomes. But questions remain. Scientists still can't say for sure how the diet does everything it seems to do — or if some parts of it do more than others. (For example, is the red meat you don't eat more important than the olive oil you do?) And if you're looking for precise rules on exactly how much to eat of exactly what foods, you won't find them here — because they don't exist.
Not to worry, though. What follows are the basic principles underlying the Mediterranean diet, and evidence suggests that following these basic principles can do you a world of good.
Why scientists got interested in the Mediterranean diet in the first place
Around the middle of the 20th century, scientists noticed that people living in Mediterranean areas had longer, healthier lives than people in many other parts of the world — even though smoking rates were high and healthcare wasn't that great in some of those countries. Some of the first hard evidence supporting this observation came from the so-called Seven Countries Study, published in 1970: It found that Greece — as exemplified by the island of Crete — had lower rates of cardiovascular disease and cancer than the other six countries in the study: the United States, Finland, the Netherlands, Italy, the former Yugoslavia and Japan.
For example, before World War II, mortality rates from heart disease and cancer were almost three times as high in the United States as in Crete. (In southern Italy, where the diet was similar to Crete's, rates were lower too.)
Though it seemed these differences might well be due, at least in part, to differences in diet, there was no firm proof: Genetics, socioeconomics and other non-diet lifestyle factors could all come into play. But now, after decades of research, scientists are more convinced that a Mediterranean diet confers multiple health benefits.
In a 2010 article in the American Journal of Clinical Nutrition, for example, researchers analyzed the results from 19 studies with more than 2 million total participants. They found that adherence to the Mediterranean diet was associated with lower overall mortality rates, as well as reduced rates of (and death from) many serious health problems, including heart disease, stroke, Alzheimer's disease and cancer.
Another analysis, published in 2011 in the Journal of the American College of Cardiology, pooled the results of 50 studies (including 35 clinical trials) with more than a half-million total participants. It found that consumers of the Mediterranean diet were less likely than others to develop high blood pressure, high insulin levels, too much fat around the waist and unhealthful cholesterol levels, or all of these clustered together (a condition known as metabolic syndrome).
The Mediterranean diet has been around, if not forever, at least for a very long time. "It developed naturally and spontaneously in the olive-growing areas of the Mediterranean basin," Trichopoulos says. People liked it and thrived on it, but then, under the influence of globalization, they gradually abandoned it.
That was a step in a very wrong direction, in the opinion of health and nutrition experts. So when they talk about the virtues of the Mediterranean diet, they're not referring to how Mediterraneans eat now but how they used to eat, up until about 50 years ago.
So what is the Mediterranean diet?
"The term 'the Mediterranean diet' is a misnomer," says Dr. Artemis Simopoulos, president of the Center for Genetics, Nutrition and Health, a nonprofit educational organization in Washington, D.C. "There are many Mediterranean diets."
After all, the cultures, religions and ethnicities in Mediterranean countries are different from one another, and, not surprisingly, to some extent the diets are different too. Wine is a major part of the diet in some countries, such as Italy and France, but not others. And even within a single country — or town, or family — not everyone eats exactly the same. To encapsulate a whole population's diet requires inferences, generalizations and judgment calls. Even among scientists, there's no universally agreed upon definition of the diet.
When they study the diet, researchers generally use scales of "Mediterranean-ness." On the most widely used of these, someone with a "perfectly Mediterranean" eating pattern would consume a high ratio of monounsaturated to saturated fats; a moderate amount of alcohol; plenty of legumes, grains, fruits, nuts, vegetables and fish; but scant meat and dairy. For the most part, these studies are done on large populations of people just living the way they normally live, and the closer those folks come to having a perfectly Mediterranean diet, the better their health and longevity tends to be.
A more detailed formulation of the Mediterranean diet — a four-tiered eating pyramid — was introduced in 1995 by scientists at the Harvard School of Public Health, the World Health Organization and Oldways Preservation and Exchange Trust, a nonprofit dedicated to changing the way people eat. An updated version was produced in 2008 and is endorsed by such respected health organizations as the Mayo Clinic and the Cleveland Clinic.
The ground floor of the 2008 version — foods you should "base every meal on" — is stuffed with fruits, vegetables, grains (mostly whole), nuts, legumes, seeds, olives, olive oil, herbs and spices. Next tier up — to be eaten next most frequently and at least twice a week — are fish and seafood. Then on level three come poultry, eggs, cheese and yogurt (daily to weekly in moderate amounts).
Perched at the very top are meats and sweets. You don't have to avoid these like the plague — just almost.
For beverages, the plan calls for water and wine (in moderation) but notes that for some people the cons of alcohol may trump the pros.
What about those icons of Italian cuisine, pasta and pizza? Well, pasta can fit the Mediterranean bill if it's whole grain. So can a pizza if it sports a whole-grain crust and a vegetarian topping, with maybe just a smidgen of cheese. (Sigh.)
Though the pyramid is based on eating habits during the early 1960s for people in Crete, much of the rest of Greece and southern Italy, scientists have tweaked it to fit with everything else they know about nutrition. For example, they suggest it may be preferable to eat low- or non-fat cheese and yogurt, which was not even possible traditionally. And while wine was historically a dietary mainstay, in the pyramid it's optional, even to be avoided in some cases.
"It was a balancing act between trying to be authentic and trying to give a healthy diet," says Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard School of Public Health and lead author of the 1995 pyramid paper. "Fortunately, there's not much tension between the two, the way there would be with, say, a North American diet."
What the Mediterranean diet is not
It's not a weight-loss diet, although if you follow the diet and restrict your calories at the same time — voila! — you can lose weight.
It's not a vegetarian or vegan diet.
And it's not a low-fat diet. It doesn't prescribe how much (or how little) fat you should consume, just where it should (and shouldn't) come from.
Can you stick to a Mediterranean diet?
No matter how good a diet is for you theoretically, it can't do you much good in reality if you can't stick to it. But Grub Med comes with considerable eat cred. Not so very long ago, populations of entire countries stuck to it for their entire lifetimes. "This is the advantage of the traditional Mediterranean diet — it is an actual diet," Trichopoulos says.
Besides, Willett notes, by using different seasonings and choosing different foods from the basic food groups, you can have a fairly un-Mediterranean-tasting Mediterranean meal. "Personally, I really like the flavors of the Mediterranean diet, but you may not want to eat it every day, and yet you can still get the health benefits."
Does every part of the diet matter?
Those who study the Mediterranean diet generally believe that all of its aspects contribute to its overall benefits. "No one part is most important," Willett says. "They're all important. It's the combination of all the parts that matters."
Most of those parts are "do's" (such as do eat lots of fruits and vegetables), but a couple are "don'ts" (such as don't eat too much meat). "It's as important for what it avoids as for what it includes," says Gregory Cole, a professor of medicine and neurology at UCLA and associate director of research at the Greater Los Angeles Veterans Administration Geriatrics Center.
Some people — even some Mediterraneans — are more Mediterranean in their eating habits than others. In general, research has shown that a little adherence to the diet gives you a little benefit, but greater adherence gives you more.
At least one study implies that some aspects of the diet may play a bigger role than others. A 2009 paper in BMJ concluded that moderate alcohol consumption was the most important (guzzling 23.5% of the credit), followed by low consumption of meat (16.6%), high consumption of vegetables (16.2%), high consumption of fruits and nuts (11.2%), high ratio of monounsaturated to saturated fats (10.6%) and high consumption of legumes (9.7%).
The other categories — grains, dairy, fish and seafood — were not found to accomplish anything much. Still, the authors did not dismiss them as unimportant to the diet because there were logical reasons why their effects might not have shown up in that population (for example, nobody ate that much fish, and low-fat dairy consumption was mixed in with consumption of high-fat dairy, which may have canceled out).
Some nutrition researchers warn against concentrating on à la carte items. "The Mediterranean diet as a whole is better than single nutrients," says Dr. Francesco Sofi, an assistant professor of clinical nutrition at the University of Florence and another prolific researcher in the field.
How does the Mediterranean diet do its good work?
Plant foods
A big chunk — fully 40% — of the credit for the reduced mortality rate associated with the Mediterranean diet can be attributed to the consumption of plant foods, according to the 2009 study that looked at the roles of various parts of the diet. (That's not including olive oil.)
Plants make antioxidants and other beneficial chemicals to protect themselves (and especially the fruits, nuts and berries of their reproductive systems) from UV rays and harmful chemicals called free radicals, which are byproducts of metabolism.
We also need these beneficial chemicals to protect ourselves from free radicals, but we can't make most of them ourselves. "Our strategy is to get them from the plants by eating them," Cole says. Some are so important we need them for normal development; we call those "vitamins." But there are many others not essential for normal maturation that nevertheless promote health, Cole says.
Plants also give us fiber (indigestible carbohydrates), which is shown to reduce the risk of heart disease, Type 2 diabetes and diverticulitis, not to mention constipation.
However, fiber may not help ward off colon cancer, its most vaunted benefit. That link was based on relatively small studies, and it hasn't panned out in more recent, larger-scale research.
Wine
Drinking alcohol, in moderation, appears to be a big player in the benefits associated with the Mediterranean diet, garnering nearly a quarter of the credit for reduced mortality in the 2009 study. Reams of research have associated moderate alcohol consumption with healthy reductions in the risk of such serious problems as heart disease, ischemic strokes (ones caused by insufficient blood flow to part of the brain), Type 2 diabetes and gallstones.
There is considerable evidence, and even more speculation, that a non-alcoholic component of red wine, resveratrol, may confer health benefits of its own. In animals though not yet in humans, the compound has been shown to increase life span and inhibit the growth of cancer cells. And in a study published just this month, a daily dose of a resveratrol supplement led to a number of positive health effects for a small group of obese men, including a reduction in their blood pressure.
Moderate alcohol consumption can also pose dangers, including an increased risk of breast cancer and, in pregnant women, of birth defects in their babies. And for some people, at least, drinking can easily progress from moderate to immoderate. (The U.S. Department of Agriculture defines moderate alcohol consumption as no more than two drinks per day for men and no more than one for women or for any adults older than 65.) For this reason, many who recommend the Mediterranean diet counsel that the alcohol component is optional.
Fat
In the early 1960s, the percentage of total calorie intake coming from fat varied widely across Mediterranean regions: from 28% in southern Italy to 40% in Crete and other parts of Greece — one-third higher than the 30% that's generally recommended today.
Yet Greek men had the highest life expectancy in the world at the time.
However much fat a Mediterranean diet includes, a lot of it is monounsaturated. That's because the diet gets most of its fat from olive oil, and most of the fat in olive oil is monounsaturated.
And not much of the fat in the Mediterranean diet is saturated because saturated fat is found mostly in foods that come from meat, dairy and poultry, and the diet minimizes those.
A high ratio of monounsaturated to saturated fat is considered an intrinsic element of the traditional Mediterranean diet — and evidence shows that it's good for people's health.
Saturated fat has detrimental effects on cholesterol levels and is associated with increased risks of heart disease and Type 2 diabetes; the opposite is true for monounsaturated fat. Monounsaturates may also help control insulin and blood sugar levels and thus help control Type 2 diabetes.
But fat — even if it's good, non-artery-clogging fat — is still high in calories. In the 1995 paper introducing the Mediterranean diet pyramid, Willett and coauthors cautioned that Mediterranean populations in the early 1960s were very active, and a 40% fat diet in a more sedentary population might have less desirable results.
Is the Mediterranean diet just about food?
No. The 2008 Mediterranean diet also recommends physical activity and mealtime sociability.
More than most diets, perhaps, the Mediterranean diet is often considered not merely a way of eating but a way of living. After all, the word "diet" comes from the Greek word "diaita," meaning lifestyle. But there's no real consensus on just how much such extracurricular elements of the diet really matter.
Some reserve judgment. "The characteristics of how people eat probably contribute something, but it's hard to quantify that," Willett says.
Others believe that though these intangibles may be incalculable, they're also invaluable. "Eating together and not alone, eating all the foods together in combination, the pleasure of eating — these are the most important features of the Mediterranean diet," Sofi says.
Δεν υπάρχουν σχόλια:
Δημοσίευση σχολίου