Implications of the ‘changing world’ for nutrition and nutritionists are considered, using the UK within a global context as an illustration. The first section summarises the slow recognition by policy makers of the significance of the changing world of food and nutrition. The second section ‘Food system stress is now at a critical level’ considers the present scale of global food system stress and the failure so far sufficiently to narrow the gap between evidence and policy change. The year 2021 was earmarked when three major UN conferences had the opportunity to chart food changes ahead. The third section ‘Multi-criteria analysis helps frame 21st century nutrition science’ proposes that multi-criteria analysis is an essential methodology for nutrition within this more complex policy world; nutrition studies can no long exclude social and environmental criteria. The penultimate section ‘Nutrition science can reconnect its life science, social and environmental nutrition traditions to contribute to new paradigm formation’ suggests that nutrition science can now recombine three traditions within its own history to address this complexity: social nutrition, environmental nutrition and life sciences. The final section ‘Priorities ahead’ concludes that this multi-criteria approach to nutrition offers new routes for science and policy influence. Five priorities are identified: (1) clarification of the features of a good food system; (2) new sustainable dietary guidelines which integrate different determinants of sustainability; (3) helping consumer engagement with change; (4) developing improved policy frameworks and (5) contributing to professional channels in these processes. In the UK, while the challenge of narrowing the gap between evidence, policy and change remains daunting, the risks of not attempting to improve the transition to an ecologically sound public health nutrition are even greater.

Major advances in biology and ecology have sharpened our understanding of what the goals of biodiversity conservation might be, but less progress has been made on how to achieve conservation in the complex, multi-sectoral world of human affairs. The failure to deliver conservation outcomes is especially severe in the rapidly changing landscapes of tropical low-income countries. We describe five techniques we have used to complement and strengthen long-term attempts to achieve conservation outcomes in the landscapes and seascapes of such regions; these are complex social-ecological systems shaped by interactions between biological, ecological and physical features mediated by the actions of people. Conservation outcomes occur as a result of human decisions and the governance arrangements that guide change. However, much conservation science in these countries is not rooted in a deep understanding of how these social-ecological systems work and what really determines the behaviour of the people whose decisions shape the future of landscapes. We describe five scientific practices that we have found to be effective in building relationships with actors in landscapes and influencing their behaviour in ways that reconcile conservation and development. We have used open-ended inductive enquiry, theories of change, simulation models, network analysis and multi-criteria analysis. These techniques are all widely known and well tested, but seldom figure in externally funded conservation projects. We have used these techniques to complement and strengthen existing interventions of international conservation agencies. These five techniques have proven effective in achieving deeper understanding of context, engagement with all stakeholders, negotiation of shared goals and continuous learning and adaptation.

Integrated crop–livestock systems are often considered a promising way to address agricultural sustainability issues. Many authors claim that complementarities and synergies between crops and livestock can improve nutrient cycling and delivery of ecosystem services (ES) in agricultural systems. They have analyzed effects of interactions at the farm level and affirmed the potential advantage of developing crop–livestock interactions at the territory level. However, potential benefits of developing synergies beyond the farm level have not been clearly identified. Thus, we developed a conceptual framework that can be used to analyze, design and perform integrated assessment of crop–livestock systems at the territory level. To address crop–livestock interaction issues, we define it as a social-ecological system called the territorial crop–livestock system (TCLS). The ecological system is represented as three interacting components, crops, grasslands and animals, allowing description of various land uses and their potential effects on nutrient cycling and ES. The social system, represented as farmers interacting with natural-resource managers and agro-food chain actors, determines land use and the nature and intensity of ES delivered. We highlight the importance of coordination and learning among actors to support implementation of complex adaptive systems such as TCLSs. We illustrate the expressive power of our conceptual framework through development of a generic typology of crop–livestock systems. Then we show how our conceptual framework can be used as an intermediary object with stakeholders in participatory design approaches. We illustrate this process by representing four archetypal TCLSs. We provide an example of the design approach implemented in Southwestern France to address severe recurrent water shortages, which includes analysis of land use in the current crop–livestock system and the associated key metabolic and ES issues, identification of options for change and multi-criteria analysis of these options. We conclude that this framework shows great potential to support development of sustainable farming systems at the territory level.