The United Nations Global Agenda for Sustainable Development, particularly through Goal 2, simultaneously seeks to end hunger, achieve food security, improve nutrition and promote sustainable agriculture. Therefore, it is crucial to focus on the agricultural production system and on consumption conditions. This means that ‘access’ to food should be determined with respect to the three dimensions of economic, physical and solidarity access to a quantity of food that fulfils both people’s nutritional needs and environmentally responsible consumption patterns. In Italy, 9.9% of the total population, i.e., six million people, live in a state of food insecurity. In Rome, 9.4% of the population lives in a condition of material deprivation, and applications for Citizens’ Income have increased, as well as food aids which amounted to EUR 20 million in 2020. The relationships between the cost of healthy and sustainable diets (which would cost 60% more than a staple diet) and the increasing economic difficulties people are facing, have prompted a focus on the multidimensional nature of food security, with particular emphasis on people’s ability to access food. In this paper, analyzing the Metropolitan City of Rome (Italy) as a case study, we present a pilot and innovative work on an affordability index to healthy and sustainable diet. A geospatial analysis highlights areas where economic difficulties in accessing food overlap with the shortage/absence of food retail outlets and with a lack of solidarity networks (e.g., civil society food distribution initiatives), allowing a new concept to come into focus, namely the blacked-out food areas. This concept helps to identify those areas in which people are socially excluded and cannot enjoy the same substantive food-related choices as people in other areas. The research outcomes provide insights into the geographical areas and neighborhoods characterized by critical access to healthy and sustainable food, providing crucial information for the planning and implementation of targeted social policies to tackle food insecurity.