Table of Contents
The Mediterranean diet is better described as a nutritional model or pattern of food consumption rather than a diet in the usual sense of the word. To begin with, there is more than one Mediterranean diet, if the phrase is understood to refer to the traditional foods and eating patterns found in the countries bordering the Mediterranean Sea. Francesco Visioli, a researcher who has edited two books on the subject, prefers the term ‘‘Mediterranean diets’’ in the plural to reflect the fact that ‘‘the populations in the Mediterranean area have different cultures, religions, economic prosperity, and [levels of] education, and all these factors have some influence on dietary habits and health.’’ For example, Visioli notes that alcohol intake is very low in the Maghreb (coastal northwestern Africa) because most inhabitants of the region are Muslim, and consequently cereal grains figure more prominently in their diet than in most other Mediterranean countries. In addition, the differences among the various forms of the Mediterranean diet are important in understanding some of the research studies that have been done on it, as will be described more fully below.
The origins of the pattern of food consumption found in Mediterranean countries go back several millennia into history; descriptions of meals in ancient Greek and Roman literature would not be out of place in contemporary Mediterranean diet cookbooks. The first description of the traditional Mediterranean diet as it was followed in the mid-twentieth century, however, was not in a cookbook; it was in a research study funded by the Rockefeller Foundation and published in 1953. The author was Leland Allbaugh, who carried out a study of the island of Crete as an underdeveloped area. Allbaugh noted the heavy use of olive oil, whole-grain foods, fruits, fish, and vegetables in cooking as well as the geography and other features of the island.
The Cretan version of the Mediterranean diet became the focus of medical research on the Mediterranean diet following the publication of Ancel Keys’s Seven Country Study in 1980. Keys (1904–2004) was a professor of physiology at the University of Minnesota who had a varied background in biology and biochemistry before turning to nutrition almost by accident. Hired by the Army in 1941 to develop portable rations for troops in combat, Keys was responsible for creating what the Army then called K rations. His next wartime project was a starvation experiment, which he conducted in order to determine the food needs of starving civilians in war-torn Europe. American soldiers who were trying to re-feed refugees in the newly liberated countries found that there was no reliable medical information about treating starvation victims. Keys recruited 36 healthy male volunteers in 1944 who were conscientious objectors, most of them from the historic peace churches. For five months the subjects were given half the normal calorie requirement of an adult male and asked to exercise regularly on a treadmill. The average weight loss was 25% of body
Based on the Mediterranean diet pyramid. (Illustration by GGS Information Services/Thomson Gale.)
weight. Three months after the experiment ended, Keys found that none of the subjects had regained their weight or physical capacity. He learned that renutrition following starvation requires several months of above-average calorie intake, that vitamin supplements are needed, and that the proportion of protein in the diet must be increased. He wrote a booklet with this information for use by relief agencies after the war ended.
In the process of studying the effects of starvation in European men who survived the war, however, Keys noticed that the rate of heart attacks among them dropped markedly as food supplies decreased. He wondered whether dietary factors might be involved in heart disease. A study of Minnesota businessmen and professors in the mid-1950s showed him that the fat content of food—particularly the saturated fats found in the meat and dairy products consumed in large amounts by Midwesterners—was indeed a factor. After that experiment, Keys began to think in terms of diet as preventive medicine. He first encountered Mediterranean diets during visits to Italy and Spain to conduct research for the World Health Organization. His studies of food consumption patterns in those countries eventually led to the Seven Countries Study, which was a systematic comparison of diet, risk factors for heart disease, and disease experience in men between the ages of 40 and 59 in eighteen rural areas of Japan, Finland, Greece, Italy, the former Yugoslavia, the Netherlands, and the United States from 1958 to 1970. (Women were not included as subjects because of the rarity of heart attacks among them at that time and because the physical examinations were fairly invasive). In addition to asking the subjects to keep records of their food intake, the researchers performed chemical analyses of the foods the subjects ate. It was found that the men living on the island of Crete—the location of Leland All-baugh’s 1953 study—had the lowest rate of heart attacks of any group of subjects in the study.
Subsequent studies of Mediterranean diets have been conducted in subjects who have already suffered heart attacks and in women subjects. One consistent finding of recent research, however, is that subjects are less healthy in the early twenty-first century than the participants of the late 1950s because the traditional diets of the Mediterranean region have been increasingly abandoned in favor of fast foods and higher consumption of fatty meat products and sweets, as well as other staples of American and Northern European diets that are high in trans-fatty acids. In addition, changing agricultural practices around the Mediterranean have resulted in poultry and meat with higher fat content than was the case in the 1960s. As a result of concern about these trends, an association for the advancement of the Mediterranean diet was formed in Spain in 1995 and later funded the Foundation for the Advancement of the Mediterranean Diet, which is presently headquartered in Barcelona. The
Foundation’s objectives include publication and dissemination of scientific findings about the diet and the promotion of its healthful use among different population groups.
Typical Mediterranean diet
In general, Mediterranean diets have five major characteristics:
- High levels of fruits and vegetables, breads and other cereals, potatoes, beans, nuts, and seeds.
- Olive oil as the principal or only source of fat in the diet.
- Moderate amounts of dairy products, fish, and poultry; little use of red meat.
- Eggs used no more than 4 times weekly.
- Wine consumed in moderate amounts—two glasses per day for men, one glass for women.
Since wine and olive oil are obtained from their respective plant sources by physical (crushing or pressing) rather than chemical processes, their nutrients retain all the properties of their sources. Wine contains polyphenols, which are powerful antioxidants and also have a relaxing effect on blood vessels, thus lowering blood pressure.
The Cretan diet
The Cretan version of the Mediterranean diet as it was used on the island in the 1960s was distinctive in several respects because it contained:
- A higher proportion of total calories from fat (40% ), almost all of it from olive oil. It was low in animal fats (butter was rarely eaten) and saturated fats.
- A relatively low level of carbohydrate intake (45% of daily calories), with most of the carbohydrates coming from fruits (2 to 3 per day) and vegetables (2 to 3 cups per day)—many of them foods with a low glycemic index. Vegetables are an integral part of meals in the Cretan diet—they are not considered side dishes.
- Generous portions of whole-grain bread (8 slices per day). The bread was made from slowly fermented dough, however, and had a lower glycemic index than most contemporary breads.
- Moderate intake of fish (about 40 grams per day), which, however, is rich in omega-3 fatty acids.
- A higher intake of meat than in most versions of the Mediterranean diet, mostly as lamb, chicken, or pork.
- High intake of alpha-linolenic acid (ALA; an omega-3 fatty acid thought to lower the risk of heart disease) from nuts (particularly walnuts), seeds, wild greens (particularly purslane [Portulaca oleracea]), and legumes. Lamb is also a good source of ALA.
Online versions of the Mediterranean diet
Two of the diets available through eDiets.com as of early 2007 are Mediterranean-type diets, the New Mediterranean Diet and the Sonoma Diet. Both plans are recipe-based, are customized to incorporate foods that the dieter enjoys, and provide personalized weekly meal plans. The New Mediterranean Diet costs $4.49 per week, with a minimum enrollment of 12 weeks, or $53.88 for the three-month trial period. The Sonoma Diet, which is an adaptation of the traditional Mediterranean diet to foods more commonly available in the United States, costs $5 per week for a minimum enrollment period of five weeks. The Sonoma Diet comes with a portion guide and wine guide as well as a customized weekly meal plan.
The function of Mediterranean diets as used in the United States and Western Europe is primarily preventive health care and only secondarily as a means to weight loss. There are several books available with weight-loss regimens based on Mediterranean diets, as well as cookbooks with recipes from a variety of Mediterranean countries.
Preventive health care
Most of the scientific research that has been done on Mediterranean diets concerns their role in preventing or lowering the risk of various diseases.
HEART DISEASE. Mediterranean diets became popular in the 1980s largely because of their association with lowered risk of heart attacks and stroke, particularly in men, following the publication of the Seven Countries study. Mediterranean diets are thought to protect against heart disease because of their high levels of omega-3 fatty acids even though blood cholesterol levels are not lowered.
ALZHEIMER’S DISEASE. A study published in Annals of Neurology in 2006 reported that subjects in a group of 2000 participants averaging 76 years of age who followed a Mediterranean-type diet closely were less likely to develop Alzheimer’s than those who did not. Further study is needed, however, to discover whether factors other than diet may have affected the outcome.
ASTHMA ANDALLERGIES. A group of researchers in Crete reported in 2007 that the low rate of wheezing and allergic rhinitis (runny nose) on the island may be related to the traditional Cretan diet. Children who had a high consumption of nuts, grapes, oranges, apples, and tomatoes (the main local products) were less likely to suffer from asthma or nasal allergies. Children who ate large amounts of margarine, however, were more likely to develop these conditions.
METABOLIC SYNDROME. Research conducted at a clinic in Naples, Italy, suggests that Mediterranean diets lower the risk of developing or reversing the effects of metabolic syndrome, a condition associated with insulin resistance and an increased risk of heart disease and type 2 diabetes. The results from this clinic were corroborated by a study done at Tufts University in Massachusetts, which found that the symptoms of metabolic syndrome were reduced even in patients who did not lose weight on the diet.
People who are making any major change in their dietary pattern in general should always consult their physician first. In addition, people who are taking monoamine oxidase inhibitors (MAOIs) for the treatment of depression should check with their doctor, as these drugs interact with a chemical called tyramine to cause sudden increases in blood pressure. Tyramine is found in red wines, particularly aged wines like Chianti, and in aged cheeses.
People using a Mediterranean diet for weight reduction should watch portion size and monitor their consumption of olive oil, cheese, and yogurt, which are high in calories. Dieters may wish to consider switching to low-fat cheeses and yogurts.
Because olive oil is a staple of Mediterranean diets, consumers should purchase it from reliable sources. The safety of olive oil is not ordinarily a concern in North America; however, samples of olive oils sold in Europe and North Africa are sometimes found to be contaminated by mycotoxins (toxins produced by molds and fungi that grow on olives and other fruits). Some mycotoxins do not have any known effects on humans, but aflatoxin, which has been found in olive oil, is a powerful carcinogen and has been implicated in liver cancer.
There are no major risks associated with following a traditional Mediterranean diet for people who have consulted a physician beforehand if they intend to use the diet as a weight-loss regimen. Health crises caused by food interactions with MAOIs are uncommon but can be fatal (about 90 deaths over a 40-year period).
The risk of cancer or any other disease from aflatoxin-contaminated olive oil is minimal in the United States and Canada.
Mediterranean diets have been the subject of more medical research since the 1960s than any other
regional or ethnic diet. Interest in Mediterranean diets has been high because nutritional research in general has moved away from curing deficiency diseases in the direction of preventive health care.
The Seven Countries Study
The results from the Seven Countries study were published in book form in 1980. The research teams found that Japanese and Greek men had far lower rates of cardiovascular disease than men from the other five other countries, with the Greek subjects from the island of Crete having the lowest rate of all. Although the study and thirty years of follow-up reports showed that the relationship among heart disease, body mass, weight, and obesity is complex, the Seven Countries research also showed that the type of fat in the diet is more important than the amount, and that the use of monounsaturated fats—particularly olive oil—is correlated with a lower risk of heart attack and stroke. The twenty-year follow-up report indicated that 81% of the difference in coronary deaths among the seven countries could be explained by differences in the average intake of saturated fatty acids.
A detailed description of the Seven Countries study, the research that preceded it, and an overview of its findings can be found online on the website of the University of Minnesota School of Public Health, Division of Epidemiology and Community Health, at <http://www.epi.umn.edu/about/7countries/index.shtm>.
The Lyon Diet Heart Study
Mediterranean diets continue to be fruitful subjects for medical investigators, partly because the countries where they originated are changing so rapidly, and partly because discussion continues as to which of the components of these diets is the most important in disease prevention. Although olive oil has been the focus of many studies, recent research done in Greece seems to indicate that the combination of the various foods and food groups in Mediterranean diets is what makes them so healthful, rather than any one specific component. This position is sometimes called the whole-diet approach.
In addition, other researchers are studying lifestyle factors other than food that may well contribute to the beneficial effects of Mediterranean cooking. These include a generally more relaxed attitude toward life; higher levels of physical activity (made possible in part by the warm sunny climate of the region); and the fasting practices of Greek Orthodox Christians, which lower fat intake and restrict the believer to a vegetarian diet for about 110 days out of every year.
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Rebecca J. Frey, Ph.D.