Today, most of the population growth is occurring in cities and especially cities in developing countries. The United Nations [1] have predicted that cities will be responsible for taking in all of the growing population in the next 40 years while also accepting the population from the rural areas. Estimates from 2018 stated that by 2050, about 50% of the world’s population will be living in cities and requiring clean water, food, energy and many other things [1]. However, data from 2021 shows that this number has already been surpassed, with 56% of the world population living in cities. The number is currently expected to rise to 68% by 2050, which would account for new 2.2 billion urban residents [2]. Cities cover only 2–3% of the land area, but they are responsible for consuming roughly 75% of the world’s energy while generating about 80% of the CO₂ emissions, massive amounts of waste and air pollution and vast water utilization [3].

As the population numbers rise, the agricultural sector is expected to produce larger quantities of food that is safe to consume and, at the same time, combat the environmental stressors of climate change and the loss of biodiversity [4]. In the process of building a modern city, many traditional and rural ties, such as localized food production, are lost as the urban residents enjoy the benefits of a globalized food system. Cities spread and take over surrounding farmlands to accommodate newcomers as they migrate from rural to urban areas. This impacts the food systems to switch to producing food based on intensive agriculture and food products that are expected to have a longer shelf life. These globalized food systems are also responsible for the overproduction of food and changes in food choices leading to overweight, obesity and malnutrition, pollution of the natural environment such as air and water and decreasing biodiversity by favoring a small number of high-yield crops ^[4][5][4,5]. Our global food system is in need of a transformation to more sustainable practices.

2. Understanding the Concept of Edible Cities

The concept of edible cities is covered in numerous research papers and has been mentioned in case studies from cities around the world. Even so, there has not been a clear, unified definition of what edible cities are, and many authors try to give their own view and include more factors that contribute to the concept of an edible city. The idea of an “edible city as nature-based solution (NbS) is to use public spaces for urban food production to generate multiple environmental, social and economic co-benefits” ^[6][11]. Moreover, it is “understood as a local, action-based strategy targeting desirable goals relevant for sustainability transformation” ^[7][14]. “In terms of edible cities, the goals are to foster social cohesion and quality of life, human-food connection (HFC) and pro-environmental behavior” ^[6][11]. Edible cities include community gardens, which are defined as “a type of open space that is planted collectively with vegetables or flowers by local members” ^[8][15], but also green roofs, green walls, urban forests, domestic gardens and historic gardens ^[9][16]. Actions to create edible cities lead to the creation of edible landscapes, “a space greened by using edible plants and other landscape plants to create a multi-functional space” ^[10][11][17,18]. Edible cities are linked to continuously productive urban landscapes, and food production is an integral part of the city that empowers local communities to overcome social problems, create new businesses and jobs, generate economic growth and foster social cohesion ^[12][19]. Edible cities encourage citizens to co-create sustainable development pathways and proactively change the urban environments to their own benefit for a more connected urban lifestyle ^[12][19]. Edible cities are closely tied to urban agriculture, as one does not exist without the other, and urban agriculture is an essential contributor to food production in edible cities, as seen in Figure 1. As urban agriculture developed, different definitions were proposed to include the innovation and social impacts of it. “Urban and peri-urban agriculture (UPA) can be defined as the growing of plants and the raising of animals within and around cities. Urban and peri-urban agriculture provides food products from different types of crops (grains, root crops, vegetables, mushrooms, fruits), animals (poultry, rabbits, goats, sheep, cattle, pigs, guinea pigs, fish, etc.) as well as non-food products (e.g., aromatic and medicinal herbs, ornamental plants, tree products). UPA includes trees managed for producing fruit and fuelwood, as well as tree systems integrated and managed with crops (agroforestry) and small-scale aquaculture” ^[13][20]. “Urban agriculture is an industry located within (intra-urban) and on the fringe (peri-urban) of a town, a city or a metropolis, which grows and raises, processes and distributes a diversity of food and non-food products, (re-)using largely human and material resources, products and services largely to that urban area” ^[14][21]. “Urban food gardening encompasses agricultural activities with generally low economic dependency on the material outputs while using food production for achieving other, mostly social, goals” ^[15][22]. Urban agriculture can bring potential risks, but stakeholders overcome them by creating a new market structure and ensuring a socially accepted development of this new form. “A food system gathers all the elements: people, environment, infrastructures, inputs, processes, institutions and activities that relate to the production, processing distribution, preparation and consumption of food, and the outputs of these activities, including socio-economic and environmental outcomes” [3], and urban food systems can be studied through four different aspects: social relevance, environmental relevance, economic relevance and spatial relevance which are presented in Figure 2 [3].

3. What Wholesome Functional Foods Can Be Utilized

United Nations are working toward protecting the environment but at the same time improving nutrition through access to food and have developed seven of the biggest priorities: (1) ending hunger and improving diets by improving conditions to grow food and encouraging agricultural advancements; (2) de-risking food systems from price spikes and food-borne illness outbreaks; (3) protecting equality and rights that affect people’s access to food, such as gender, ethnicity and age; (4) boosting bioscience to restore soils, breed and recarbonize the soil more efficiently; (5) protecting resources by offering sustainable solutions for agricultural problems such as irrigation, fertilization, drought and pests; (6) sustaining aquatic food, as fish and shellfish are an important source of energy and protein; and, lastly, (7) harnessing digital technology such as robots and artificial intelligence to increase the yield of plants and the health of animals ^[16][23]. At the same time, we can see that consumers are more interested in complex food that, apart from nutritional value, provides prohealthy aspects. This kind of function is what makes a food “functional”. “A food can be regarded as functional if it is satisfactorily demonstrated to affect beneficially one or more target functions in the body, beyond adequate nutritional effects, in a way that is relevant to either improved state of health and well-being and/or reduction of risk of disease. A functional food must remain food and it must demonstrate its effects in amounts that can normally be expected to be consumed in the diet: it is not a pill or a capsule, but part of the normal food pattern” ^[16][23]. Functional food can be whole food, fortified, enriched, enhanced or altered food products ^[17][24]. It can also include medical food and foods for special dietary use. However, products that are called functional foods in the European Union must first of all comply with the requirements of the Regulation 1924/2006 on nutrition and health claims made on foods ^[18][25]. Functional foods are associated with sustainable food production as they focus on the use of raw materials that are produced naturally or with minimal processing to preserve the high qualities naturally present in the product ^[19][26]. Additionally, the waste from fruits and vegetables such as peels, leaves, seeds and pulps can be rich in active substances for functional foods and can therefore be reintroduced into the production process ^[20][27]. Examples of functional foods include products or foods that contain omega-3 fatty acids, probiotics, plant sterols, plant stanols, tea that contains catechins or berries that are rich in anthocyanins ^[21][28]. Many active substances can be found in plants and their products that have a beneficial effect on human health that are eligible to be grown or are already being grown in urban environments. Table 1 shows examples of plants, highlighting the active substances contained in some parts of the plant with health-promoting potential, which can be grown in urban spaces in different latitudes. Compared to the baseline diet, which was balanced according to healthy eating recommendations, the introduction of functional foods into the diet helped to reduce some micronutrient deficiencies and meet the recommended intake more effectively ^[22][29].