Cities and metropolitan areas are essential to sustainable development, especially in managing nutrient flows such as fertilizers, food, and organic waste. However, integrating urban metabolism and nutrient circularity into planning remains challenging due to fragmented approaches. As cities grow and face climate change, the key question is: how can urban strategies better incorporate nutrient circularity? This research identifies and measures factors influencing nutrient flow management, proposing a three-step approach: identifying key factors, assessing them with a planning focus, and integrating findings into strategic planning. The focus is on South America, given its significant role in agrifood production and urbanization. Article 1: This study develops a framework to measure Nutrient Circularity Capacity (NCC) in South American metropolitan areas (SAMAs), evaluating environmental, technical, economic, social, and political factors. It identifies 12 influencing factors across four themes—Material Flow, Food & Feed Value Chain, Knowledge Base, and Institutional Support—and links them to 11 indicators using multi-criteria analysis. Results show Montevideo, Uruguay, leading in NCC due to government support and innovation, while Paraguay and Bolivia rank lowest. The study emphasizes the need for localized strategies, with investments in innovation, waste management, and peri-urban agriculture as critical elements for improving nutrient circularity in the region. Article 2: This research introduces a multidimensional diagnostic framework to enhance nutrient circularity in urban planning, bridging the gap between urban metabolism and practical planning. Applied to the Metropolitan Region of Santiago de Chile (MRSC), the framework assesses nitrogen (N), phosphorus (P), and potassium (K) flows across spatial, material, and social dimensions. Utilizing the UN's *Our City Plans* toolbox, data from local databases, literature, and 34 interviews helped map the agri-food-w