The Mediterranean diet is much more than a food pattern and certainly not a restrictive food intake regimen. In the Mediterranean diet’s concept, “food” is one piece of a large mosaic involving strong bonds to nature (sustainable agriculture, seasonality, agri-biodiversity), social features (e.g., communal festivities related to harvest seasons and religions), landscape (combining the works of humans and nature, as can be seen in geoparks of the area), architecture (use of locally sourced stones, whitewash, ceramic tiles), history (birthplace of important civilizations), art (music, crafts), and more.

The Mediterranean diet (MD) is defined, in its broad sense, by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as involving “a set of skills, knowledge, rituals, symbols and traditions concerning crops, harvesting, fishing, animal husbandry, conservation, processing, cooking, and particularly the sharing and consumption of food. Eating together is the foundation of the cultural identity and continuity of communities throughout the Mediterranean basin” [1].

Bach-Faig and colleagues ^[2] described the MD as a dietary pattern and associated lifestyle that adopts mainly plant foods. It is rich in fruits, vegetables, bread, pasta, rice, couscous, and other cereals, as well as olives, nuts, seeds, herbs, spices, garlic, onions, legumes, potatoes, and more. Olive oil is the main fat, and ‘biodiversity’ and seasonality define this dietary pattern, which embraces a wide variety of plant foods of local origin and their seasonal character. This high agri-biodiversity mostly results from the adaptation of plants brought from different geographical locations that became indigenous and further diverged into cultivars. In the cuisine, this multitude of locally available ingredients ^[3] translates into varied textures, flavors, and colors, according to regional traits and preferences. Some people might believe these regional variations constitute different food habits, but they actually share the same principles and pillars and are hence facets of the Mediterranean diet ^[1][2][3][4]. In other words, such food habits share well-acknowledged features across their territories of origin, together forming the big picture of the Mediterranean diet ^[2][4][5][6]. Its diversity consists of enjoyable and affordable healthy dishes, which are quick and easy to prepare with local and seasonal ingredients, and which also help to strengthen social ties ^[7].

Bach-Faig and colleagues [2] described the MD as a dietary pattern and associated lifestyle that adopts mainly plant foods. It is rich in fruits, vegetables, bread, pasta, rice, couscous, and other cereals, as well as olives, nuts, seeds, herbs, spices, garlic, onions, legumes, potatoes, and more. Olive oil is the main fat, and ‘biodiversity’ and seasonality define this dietary pattern, which embraces a wide variety of plant foods of local origin and their seasonal character. This high agri-biodiversity mostly results from the adaptation of plants brought from different geographical locations that became indigenous and further diverged into cultivars. In the cuisine, this multitude of locally available ingredients [3] translates into varied textures, flavors, and colors, according to regional traits and preferences. Some people might believe these regional variations constitute different food habits, but they actually share the same principles and pillars and are hence facets of the Mediterranean diet [1,2,3,4]. In other words, such food habits share well-acknowledged features across their territories of origin, together forming the big picture of the Mediterranean diet [2,4,5,6]. Its diversity consists of enjoyable and affordable healthy dishes, which are quick and easy to prepare with local and seasonal ingredients, and which also help to strengthen social ties [7].

In short, the Mediterranean diet, as defined by UNESCO, encompasses a lifestyle that goes beyond a mere diet ^[4][6][7], and it is acknowledged by international organizations as beneficial to human health and the environment ^{[6][8][9][10]}. High adherence scores to this dietary pattern have been shown to significantly improve the nutritional and health status of populations ^{[11][12][13][14][15][16]}, while causing low impacts on the environment ^{[17][18][19][20]} and even contributing to the safeguarding of agri-biodiversity ^[21][22][23].

In short, the Mediterranean diet, as defined by UNESCO, encompasses a lifestyle that goes beyond a mere diet [4,6,7], and it is acknowledged by international organizations as beneficial to human health and the environment [6,8,9,10]. High adherence scores to this dietary pattern have been shown to significantly improve the nutritional and health status of populations [11,12,13,14,15,16], while causing low impacts on the environment [17,18,19,20] and even contributing to the safeguarding of agri-biodiversity [21,22,23].

This valuable food pattern has been continuously threatened, directly and indirectly, by the vulgarization of ultra-processed foods, by consumers’ misinformation, and by the still insufficient actions to ensure safe and sustainable food for all, as stated in the second sustainable development goal (SDG 2) ^[24]. However, since food systems are complex, cross multiple SDGs, and affect us all, in 2020 and 2021, action tracks were identified and commitments were made to raise awareness of existing sustainable dietary patterns, such as the MD ^[6][25], and to underpin policies with science ^{[25][26][27][28]}.

This valuable food pattern has been continuously threatened, directly and indirectly, by the vulgarization of ultra-processed foods, by consumers’ misinformation, and by the still insufficient actions to ensure safe and sustainable food for all, as stated in the second sustainable development goal (SDG 2) [24]. However, since food systems are complex, cross multiple SDGs, and affect us all, in 2020 and 2021, action tracks were identified and commitments were made to raise awareness of existing sustainable dietary patterns, such as the MD [6,25], and to underpin policies with science [25,26,27,28].

Efforts to safeguard the MD in Portugal and to improve its adherence scores have been acknowledged; hence, Portugal is herein taken as a case study for the baseline period of 2015–2016.

This entry starts by introducing the historical context and the main features of the Mediterranean diet. Special attention was paid to the characterization of the baseline because of its relevance in assessing the effectiveness of policies and actions to comply with the UN, European community (EC), and national agendas with respect to sustainable food systems. The prospective use of a composite indicator combining data from different sources is herein considered for the baseline period, and finally, the advantages and limitations are analyzed and discussd of the selected metrics in assessing the economic and social sustainability, nutritional aspects, and ecological footprint of the MD in Portugal.

This entry starts by introducing the historical context and the main features of the Mediterranean diet. Special attention was paid to the characterization of the baseline because of its relevance in assessing the effectiveness of policies and actions to comply with the UN, European community (EC), and national agendas with respect to sustainable food systems. The prospective use of a composite indicator combining data from different sources is herein considered for the baseline period, and finally, we analyzes and discusses the advantages and limitations of the selected metrics in assessing the economic and social sustainability, nutritional aspects, and ecological footprint of the MD in Portugal.

With the present work, this entry aims to contribute to the discussions on how to assess the implementation of sustainable diets and supporting food systems, now and in the future.