1.1 Definitions and History of the Mediterranean Diet
The Mediterranean Diet is a widely used concept that has been used over the last few decades by doctors, researchers, nutritionists, dietitians, and experts from various fields, even though there is no clear consensus on its definition.
The healthy-eating model called the Mediterranean Diet dates back to the early 1960s, when Keys et al. traveled through southern European countries and started the Seven Countries Study. This study, which was the first piece of research into the Mediterranean Diet, began in 1958 and demonstrated that the mortality rate from coronary heart disease in southern Europe was two to three times lower than in northern Europe or the United States [1,2]. It also described low rates of coronary heart disease in the Mediterranean regions when contrasted with other study populations [2,3], and was the main source of information regarding traditional Mediterranean diets in the 1960s and 1970s [4].
In this context, the Mediterranean Diet was defined as the eating habits observed in Greece and Southern Italy in the late 1950s and early 1960s, when the effects of World War II had passed but the fast-food culture had not yet invaded the area [5].
Seen from another point of view the Mediterranean Diet could be also defined by its clearly beneficial health effects. The first results of the Seven Countries Study showed that there was an association between this traditional dietary pattern and a low incidence, and prevalence of mortality rates from coronary heart diseases, other cardiovascular diseases, and low all-cause mortality, including cancer [6].
In general, the term Mediterranean Diet refers to dietary patterns found in the olive tree-growing areas of the Mediterranean basin before the mid-1960s [7].
Although this concept is a clear combination of history, culture, and environment and implies a common dietary pattern in Mediterranean countries, there are however important differences in typical products, food cultures, traditions, and geographical and ecological environments between regions [8].
From these various approaches, it can be said that there is no single Mediterranean Diet and that there are major differences in the traditional eating habits of citizens from countries bordering the Mediterranean Sea: Italy, Greece, France, Spain, North Africa, and the Eastern basin [9].
Even the dietary practices within the same country can vary considerably. Notwithstanding these differences, however, olive oil has always had a central position in all Mediterranean countries or regions [10].
A recent review considers the Mediterranean Diet as an intangible and sustainable food culture transmitted from generation to generation over centuries, of landscapes, places, knowledge, know-how, technologies, products, food preparation and intake, myths and beliefs, accents, creativity, and hospitalities [11,12]. Indeed, since November 16, 2010, the Mediterranean Diet has been inscribed into UNESCO’s Representative List of Intangible Cultural Heritage of Humanity [13]. The objective of this initiative was to safeguard the immense legacy representing the cultural value of the Mediterranean Diet, as well as to share and disseminate its values and benefits internationally.
In conclusion, the Mediterranean Diet is essentially part of a lifestyle and requires the simultaneous consideration of other nondietary behavioral factors when assessing its beneficial health effects [14]. Unfortunately, over the last decades, current diets in Mediterranean countries are departing from the traditional Mediterranean Diet toward an unhealthier eating model. This is due to the widespread dissemination of Western-type culture, along with the globalization of food production and consumption, which is related to the homogenization of food behavior in the modern era [8,15].
Therefore, it may now be time to update the definition of the Mediterranean Diet [16,17].
1.2 Mediterranean Diet: Characteristics
In the mid-20th century Mediterranean peoples frequently consumed high amounts of plant foods (olive oil, fruits, vegetables, legumes, fruits, bread, cereal products, nuts, and seeds), food from animals in limited amounts (fish, meat, and milk and milk products), wine, and had a low intake of saturated fats [6].
Taking into account all these characteristics and using a somewhat reductionist approach, this dietary pattern can be considered to be mainly, but not dogmatically, an exclusively plant-based dietary pattern. However, it has been pointed out that the Mediterranean Diet is not a vegetarian diet, in spite of the fact that two of its most common and typical foods, olive oil and wine, are plant products [14].
Therefore, the traditional Mediterranean Diet favored the consumption of locally grown, seasonally fresh and minimally processed foods and was consumed by physically active people [10].
The main and typical foods of the traditional diet of Mediterranean countries are:
• Vegetables and fruits. These are important sources of minerals, vitamins, antioxidants, and fiber. Furthermore, the benefits of their consumption are amplified if they are cooked or dressed with olive oil. Other healthy vegetable options are raw foods such as salads.
• Grains. The nutritional composition of grains may vary depending on the variety and environmental growing conditions. In general, cereal grains are high in carbohydrates, low in fat, good sources of protein and provide varying amounts of fiber, vitamins, and minerals. Cereal products should contain whole grains, including wheat, oats, rice, rye, barley, and corn. Grains should also be consumed in minimally processed forms.
• Olives and olive oil. By definition, olive oil is a central component in the cuisine of the countries surrounding the Mediterranean Sea. This type of vegetable oil has a peculiar fatty acid composition (with a large proportion of monounsaturated fat—mainly oleic acid—and a relatively low proportion of saturated fat) and also contains other minor compounds (tocopherols and carotenoids among others) with antioxidant properties. Olive oil is the principal source of dietary fat used to dress salads and vegetables, and in cooking or baking. The variety “extra-virgin” olive oil is highest in health promoting fats, phytonutrients, and other important micronutrients.
• Nuts, legumes, and seeds. All of these foods are packed with vitamins and minerals. Nuts and seeds also provide healthy mono- and polyunsaturated plant oils as well as protein. Legumes, which include beans, are filling and also contain lean protein.
• Fish and shellfish are preferred over meat in the traditional Mediterranean diet, although the amount of fish consumed varies widely between and within Mediterranean countries. This group of foods is an important source of healthy protein and essential heart-healthy omega-3 fatty acids.
• Cheese and yogurt. Dairy products, from a variety of animals, principally in the form of yogurt and cheese, are consumed in low to moderate amounts.
• Eggs are an excellent source of high-quality protein and also contain a number of healthy nutrients, including B vitamins and protein.
• Meat. In general, the consumption of red meat and processed meats is lower in the Mediterranean population than the consumption of white meat, in spite of the fact that red meat is a good source of animal protein.
• Wine. Moderate wine drinking in the context of the meals has been a long-standing tradition in the Mediterranean basin, with the exception of Islamic populations of this area.
• Herbs and spices add flavors and aromas to foods, reducing at the same time the need to add salt or fat when cooking. Herbs and spices are very common in Mediterranean cuisine; they contain several health-promoting antioxidants and contribute to the differences between the broad varieties of culinary cultures.