Mediterranean Diet

Definition

Origins

The origins of the pattern of food consumption found in Mediterranean countries go back several millennia; 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 and 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 to determine the food needs of starving civilians in war-torn Europe. American soldiers who were trying to 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 weight. Three months after the experiment ended, Keys found that none of the subjects had regained their weight or physical capacity. He learned that nutrition 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 (WHO). 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. The researchers found that the men living on the island of Crete, the location of Leland Allbaugh's 1953 study, had the lowest rate of heart attacks of any group of subjects in the study.




Mediterranean diet





Mediterranean diet

Description

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 dietary habits differ within communities. For example, Visioli notes that alcohol intake is very low in the Maghreb area (coastal northwestern Africa) because most inhabitants of the region are Muslim; 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.

Typical Mediterranean diet

In general, Mediterranean diets have eight major characteristics:

Because 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:

The Mediterranean Diet Pyramid

The lowest level of the pyramid adds such cultural and social elements as “adequate rest” and “conviviality” (eating the meal in a congenial social group) to “regular physical activity,” and adds a side note to remind readers of the importance of choosing traditional, local, and eco-friendly foods in season. Immediately above this level is an added layer illustrating the importance of proper hydration; a pitcher, glasses, and a cup filled with a hot beverage depict water and herbal infusions. The FDM website suggests drinking 1.5 to 2 liters (about 1.5–2 qt) of water daily.

The third layer from the bottom consists of all fruits and vegetables; the pyramid indicates that “this group should be served at every main meal.” The next level is divided into two sub-layers, olives, nuts, and seeds; and dairy products. Foods in these two groups are to be eaten every day. The next level upward, foods to be eaten on a weekly basis, is divided into three sublayers: eggs and legumes, two to four servings per week; poultry and seafood, two servings per week; red and processed meats, no more than two servings; and potatoes, no more than three servings. At the top of the pyramid are sweets, no more than two servings per week.

Function

The function of Mediterranean diets as used in the United States and Western Europe is primarily preventive health care and only secondarily for weight loss. Several books are available with weight-loss regimens based on Mediterranean diets, as well as cookbooks with recipes from a variety of Mediterranean countries.

Benefits

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 strokes, 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. As of 2018, however, the American Heart Association (AHA) notes that “the diets of Mediterranean peoples contain a relatively high percentage of calories from fat. This is thought to contribute to the increasing obesity in these countries, which is becoming a concern.” The AHA adds, “Before advising people to follow a Mediterranean diet, we need more studies to find out whether the diet itself or other lifestyle factors account for the lower deaths from heart disease.”

Interestingly, a recent study carried out in the United Kingdom underscores the importance of social support in encouraging adults at high risk of cardiovascular disease to adopt a Mediterranean diet. The researchers found that face-to-face meetings were more effective in motivating group members to follow a Mediterranean diet than either telephone or Internet contact. In addition, a team of researchers in Greece reported in 2017 that such lifestyle factors as regular sleep and an active social life were as much a part of lowering the risk of heart disease among adults living in this Mediterranean country as following a Mediterranean dietary pattern. Other lifestyle factors credited with lowering the risk of heart disease in Mediterranean countries 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.

ALZHEIMER'S DISEASE. Mediterranean diets have been studied for their potential benefits to the aging brain. One difficulty in this area of research has been closely defining the specific form of the diet and the specific population chosen for the study to ensure the data is meaningful. One recent study conducted in Greece limited study participants to elderly persons from a specific region who had followed a defined Mediterranean diet pattern. The researchers found that adherence to this Greek form of the Mediterranean diet “is associated with better cognitive performance and lower dementia rates in Greek elders.” Another difficulty in research related to dementia is evaluating whether adherence to a Mediterranean diet actually causes improvement in cognitive function or is simply correlated with cognition without having a cause-and-effect relationship with it. A research team in the United Kingdom states: “More controlled trials are required to establish a causational relation.”

KEY TERMS
Crohn's disease—
A type of inflammatory bowel disease characterized by fever, diarrhea (often bloody), abdominal cramping, and weight loss.
Gluten—
A mixture of proteins found in wheat, rye, barley, and oats that can trigger celiac disease (an autoimmune disorder of the small intestine) and other intestinal disorders in susceptible people.
Legume—
Any plant belonging to the family Fabaceae. Legumes are grown for their grain seeds and for livestock forage; they include chickpeas, alfalfa, lentils, clover, peas, beans, soybeans, and peanuts.
Metabolic syndrome—
A condition characterized by abdominal obesity, high blood pressure, high blood sugar levels, and high blood levels of fatty molecules (triglycerides). It increases a person's risk of type 2 diabetes.
Monoamine oxidase inhibitors (MAOIs)—
A class of antidepressant drugs that inhibit the action of specific enzymes. They are generally used as drugs of last resort for depression because of their potential to interact with tyramine in the diet and lead to severe hypertension.
Nonalcoholic fatty liver disease—
A liver disorder that occurs when fat is deposited in the liver for reasons other than alcohol consumption. It is the most common liver disorder in the developed countries and is closely related to the metabolic syndrome and type 2 diabetes.
Observational study—
A study in which the researchers simply observe the symptoms or behaviors of interest to them in their group of subjects without trying to influence, medicate, or otherwise change the symptoms or behaviors.
Tyramine—
A compound derived from the amino acid tyrosine. It is found naturally in cheeses, some types of red wine, and other foods, and can interact with MAO inhibitors to cause a dangerous rise in blood pressure.

ASTHMA AND ALLERGIES. The evidence that Mediterranean diets can prevent childhood asthma and other allergies is mixed as of 2018. A number of observational studies have reported that Mediterranean diets have a protective effect against asthma in children, whereas other research groups have found no such effect. The authors of a recent Australian study point out, however, that no randomized controlled trials of the relationship between Mediterranean diets and childhood asthma have been conducted and recommend that these be undertaken to provide solid evidence in either direction.

METABOLIC SYNDROME. Following a Mediterranean diet is associated with a lowered risk of metabolic syndrome, a condition associated with insulin resistance and an increased risk of heart disease and type 2 diabetes. A study of adults from the Balearic Islands, an archipelago near the eastern coast of Spain, reported in 2018 that the risk of metabolic syndrome increased not only with the age of the subjects but also with their decreased adherence to a Mediterranean diet. A similar study carried out in Italy also reported that adherence to a Mediterranean diet lowered the subjects' risk of developing metabolic syndrome.

Precautions

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 when these drugs interact with a chemical called tyramine, they 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.

People who are sensitive to gluten should consult a dietitian or their physician before starting a Mediterranean diet, as the whole-grain breads and pasta that are staples of these diets almost always contain gluten.

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). Aflatoxin, a mycotoxin that has been found in olive oil, is a powerful carcinogen and has been implicated in liver cancer.

Risks

No major risks are 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.

Research and general acceptance

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 and toward 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 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 indicated 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.

The Lyon Diet Heart Study

The Lyon Diet Heart Study was the first clinical trial to demonstrate the beneficial effects of a Mediterranean-type diet. Begun in 1995, it was a major investigation into the effectiveness of a modified Cretan diet in preventing recurrent heart attacks. The subjects were a group of 605 Frenchmen under 70 years of age who had been treated in the previous six months for a heart attack. They were recruited from several hospitals in the area of Lyon, a city in east-central France. Half the subjects were given an hour-long educational introduction to a modified version of the Cretan diet (canola oil was substituted for olive oil) and advised to follow this Mediterranean-style diet. The other half (the control group) were given a prudent diet recommended by the American Heart Association (AHA). At the end of four years, overall death rates were 56% lower in the group that followed the modified Cretan diet.

QUESTIONS TO ASK YOUR DOCTOR
Ongoing research

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. Other investigators note that the sheer variety of nutrients and phytochemicals in the Mediterranean diet complicates understanding how the components of the Mediterranean diet may have protective effects at the molecular level.

See also Antioxidants ; Arthritis diet ; Cancer ; Cancer diet ; DASH diet ; French paradox ; Greek and Middle Eastern diet ; Low-fat diet ; Omega-3 and omega-6 fatty acids ; Ovolactovegetarianism ; Sonoma diet ; Sustainable diets ; Vegetarianism ; Vitamin B12 ; Vitamin E .

Resources

BOOKS

Acquista, Angelo. The Mediterranean Family Table: 125 Simple, Everyday Recipes Made with the Most Delicious and Healthiest Food on Earth. New York: William Morrow, 2015.

Delgado, Amelia, editor. Chemistry of the Mediterranean Diet. New York: Springer, 2016.

Ewald, Bay. The Modern Mediterranean Diet: The Delicious Way to Eat, Drink, and Live Well. Berkeley, CA: Ulysses, 2015.

Passedat, Gérard. Flavors from the French Mediterranean. Translated by Julia Chalkley. Paris: Flammarion, 2016.

Walton, Catherine, editor. The Mediterranean Diet: Perspectives, Food Components, and Health Effects. New York: Nova Biomedical, 2017.

PERIODICALS

Anastasiou, Costas A., Mary Yannakoulia, Mary H. Kosmidis, et al. “Mediterranean Diet and Cognitive Health: Initial Results from the Hellenic Longitudinal Investigation of Ageing and Diet.” PLoS One 12, no. 8 (August 1, 2017): e0182048.

Castro-Rodriguez, Jose A., and Luis Garcia-Marcos. “What Are the Effects of a Mediterranean Diet on Allergies and Asthma in Children?” Frontiers in Pediatrics 5 (April 21, 2017): 72.

Corella, Delores, Oscar Coltell, Fernando Macian, et al. “Advances in Understanding the Molecular Basis of the Mediterranean Diet Effect.” Annual Review of Food Science and Technology 9 (March 25, 2018): 227–49.

Erwin, C. M., et al. “A Qualitative Analysis Exploring Preferred Methods of Peer Support to Encourage Adherence to a Mediterranean Diet in a Northern European Population at High Risk of Cardiovascular Disease.” BMC Public Health 18 (February 5, 2018): 213.

Georgousopoulou, E. N., E. Polychronopoulos, S. Tyrovolas, et al. “Mediterranean Lifestyle and Cardiovascular Disease Prevention.” Cardiovascular Diagnosis and Therapy 7, suppl. 1 (April 2017): S39–S47.

Godos, Justyna, Gaetano Zappalá, Sergio Bernardini, et al. “Adherence to the Mediterranean Diet Is Inversely Associated with Metabolic Syndrome Occurrence: A Meta-Analysis of Observational Studies.” International Journal of Food Sciences and Nutrition 68, no. 2 (March 2017): 138–48.

Papamichael, Maria M., Catherine Itsiopoulos, Nugroho H. Susanto, et al. “Does Adherence to the Mediterranean Dietary Pattern Reduce Asthma Symptoms in Children? A Systematic Review of Observational Studies.” Public Health Nutrition 20, no. 15 (October 2017): 2722–34.

Petersson, S. D., and E. Philippou. “Mediterranean Diet, Cognitive Function, and Dementia: A Systematic Review of the Evidence.” Advances in Nutrition 7, no. 5 (September 15, 2016): 889–904.

Sureda, Antoni, Maria Bibiloni, Alicia Julibert, et al. “Adherence to the Mediterranean Diet and Inflammatory Markers.” Nutrients 10, no. 2 (January 10, 2018): E62.

WEBSITES

American Heart Association (AHA). “Mediterranean Diet.” Heart.org . http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/Nutrition/Mediterranean-Diet_UCM_306004_Article.jsp# (accessed May 12, 2018).

Ansel, Karen. “Make It Mediterranean.” Academy of Nutrition and Dietetics, Kids Eat Right. https://www.eatright.org/food/planning-and-prep/cooking-tipsand-trends/make-it-mediterranean (accessed May 12, 2018).

Fundación Dieta Mediterránea [Mediterranean Diet Foundation]. “What's the Mediterranean Diet?” Generalitat de Catalynya, Departament d'Agricultura. https://dietamediterranea.com/en/nutrition/ (accessed May 12, 2018).

Mayo Clinic staff. “Mediterranean Diet: A Heart-healthy Eating Plan.” Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/mediterranean-diet/art-20047801 (accessed May 12, 2018).

Robinson, Kara Mayer. “Mediterranean Diet—Topic Overview.” WebMD. https://www.webmd.com/heartdisease/tc/mediterranean-diet-topic-overview#1 (accessed May 12, 2018).

United Nations Educational, Scientific, and Cultural Organization. “Intangible Cultural Heritage: Mediterranean Diet.” UNESCO.org . https://ich.unesco.org/en/RL/mediterranean-diet-00884 (accessed May 12, 2018).

ORGANIZATIONS

Academy of Nutrition and Dietetics, 120 S. Riverside Plaza, Ste. 2190, Chicago, IL, 60606-6995, (312) 899-0040, (800) 877-1600, amacmunn@eatright.org, http://www.eatright.org .

American Heart Association, 7272 Greenville Ave., Dallas, TX, 75231, (888) 242-8883, help@onlineaha.org, https://www.onlineaha.org .

Fundación Dieta Mediterránea [Mediterranean Diet Foundation], Johann Sebastian Bach, 28, Barcelona, Spain, 08021, +34 934 143 158, info@dietamediterranea.com, https://dietamediterranea.com/en/ .

Rebecca J. Frey, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.